Key Questions in Surgical Critical Care [1 ed.] 9781841100920, 1841100927

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KEY QUESTIONS IN SURGICAL CRITICAL CARE

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KEY QUESTIONS IN SURGICAL CRITICAL CARE by

M r Robert U. Ashf ord M RCS(Glasg) Specialist Regist rar in Trauma & Ort hopaedics York Dist rict Hospit al Yorkshire Deanery UK

Dr T. Neal Evans FRCA Specialist Regist rar in Anaest hesia Oxf ord Radcliff e Hospit als Oxf ord Deanery UK

Dr R. Andrew Archbold M RCP Specialist Regist rar in Cardiology London Chest Hospit al London Deanery (Nort h) UK

London ♦ San Francisco

www.greenwich-medical.co.uk

© 2003 Greenw ich M edical M edia Limit ed 137 Eust on Road, London NW1 2AA 870 M arket St reet , St e 720 San Francisco, CA 94102 ISBN 1 84110 0927 First Published 2003 While t he advice and inf ormat ion in t his book is believed t o be t rue and accurat e, neit her t he aut hors nor t he publisher can accept any legal responsibilit y or liabilit y f or any loss or damage arising f rom act ions or decisions based in t his book. The ult imat e responsibilit y f or t he t reat ment of pat ient s and t he int erpret at ion lies w it h t he medical pract it ioner. The opinions expressed are t hose of t he aut hors and t he inclusion in t his book of inf ormat ion relat ing t o a part icular product , met hod or t echnique does not amount t o an endorsement of it s value or qualit y, or of t he claims made by it s manuf act urer. Every eff ort has been made t o check drug dosages; how ever, it is st ill possible t hat errors have occurred. Furt hermore, dosage schedules are const ant ly being revised and new side-eff ect s recognised. For t hese reasons, t he medical pract it ioner is st rongly urged t o consult t he drug companies' print ed inst ruct ions bef ore administ ering any of t he drugs ment ioned in t his book. Apart f rom any f air dealing f or t he purposes of research or privat e st udy, or crit icism or review, as permit t ed under t he UK Copyright Designs and Pat ent s Act 1988, t his publicat ion may not be reproduced, st ored, or t ransmit t ed, in any f orm or by any means, w it hout t he prior permission in w rit ing of t he publishers, or in t he case of reprographic reproduct ion only in accordance w it h t he t erms of t he licences issued by t he appropriat e Reproduct ion Right s Organisat ions out side t he UK. Enquiries concerning reproduct ion out side t he t erms st at ed here should be sent t o t he publishers at t he London address print ed above. The right s of Robert Ashf ord, Neal Evans and Andrew Archbold t o be ident if ied as aut hors of t his Work have been assert ed by t hem in accordance w it h t he Copyright Designs and Pat ent s Act 1988. The publisher makes no represent at ion, express or implied, w it h regard t o t he accuracy of t he inf ormat ion cont ained in t his book and cannot accept any legal responsibilit y or liabilit y f or any errors or omissions t hat may be made. A cat alogue record f or t his book is available f rom t he Brit ish Library. Typeset by M izpah Publishing Services, Chennai, India Print ed by The Alden Group Lt d, Oxf ord Dist ribut ed by Plymbridge Dist ribut ors Lt d and in t he USA by Jamco Dist ribut ion

Contents Pref ace ..........................................................................................................vi The Examinat ion ..........................................................................................vii List of Abbreviat ions ....................................................................................ix Acknow ledgement s ....................................................................................xiii Section 1 – MCQs Cardiovascular Syst em – Quest ions ..............................................................3 Respirat ory Syst em – Quest ions ..................................................................21 Ot her Syst ems and M ult isyst em Failure – Quest ions ................................36 Problems in Int ensive Care – Quest ions......................................................52 Principles of Int ensive Care – Quest ions ....................................................55 Pract ical Procedures – Quest ions ................................................................61 Cardiovascular Syst em – Answ ers................................................................63 Respirat ory Syst em – Answ ers ....................................................................90 Ot her Syst ems and M ult isyst em Failure – Answ ers..................................111 Problems in Int ensive Care – Answ ers ......................................................130 Principles of Int ensive Care – Answ ers......................................................133 Pract ical Procedures – Answ ers ................................................................140 Section 2 – Vivas Cardiovascular Syst em – Quest ions ..........................................................145 Respirat ory Syst em – Quest ions ................................................................147 Ot her Syst ems and M ult isyst em Failure – Quest ions ..............................149 Problems in Int ensive Care – Quest ions....................................................151 Principles of Int ensive Care – Quest ions ..................................................152 Pract ical Procedures – Quest ions ..............................................................153 Cardiovascular Syst em – Answ ers..............................................................155 Respirat ory Syst em – Answ ers ..................................................................170 Ot her Syst ems and M ult isyst em Failure – Answ ers..................................202 Problems in Int ensive Care – Answ ers ......................................................223 Principles of Int ensive Care – Answ ers......................................................225 Pract ical Procedures – Answ ers ................................................................230 v

Preface Post graduat e surgical examinat ions t ake t he f orm of mult iple-choice quest ions, viva voce examinat ions and clinicals. In all t he Royal Colleges, a key component of t he f irst t w o of t hese sect ions is crit ical care. This book is a companion t o Surgical Crit ical Care, by Robert Ashf ord and Neal Evans, published by Greenw ich M edical M edia Lt d in 2001, and examines all aspect s of t he subject t hat may be assessed. This book is split int o t w o sect ions: mult iple-choice quest ions and viva t opics. Based upon t he syllabus of t he Royal College of Surgeons of England, each of t hese t w o sect ions is sub-divided int o t he same six sect ions as Surgical Crit ical Care. Each answ er is cross-ref erenced t o specif ic pages in Surgical Crit ical Care (using t he SCC icon) as w ell as being elaborat ed upon. The mult iple-choice quest ions are of a mult iple t rue/f alse t ype. M arking should be in t he f orm of t he examinat ion you are sit t ing. Remember some of t he Royal Colleges employ negat ive marking, w hich is designed t o prevent t he candidat e f rom guessing. The viva t opics are quest ions t ypical of t hose you may be asked in t he examinat ion. This book does not aim t o be a def init ive t ext book f or t he M RCS examinat ion. It is designed as a revision aid and t o st imulat e self -assessment . Good luck! R.U.A. T.N.E. R.A.A. Oct ober 2002

vi

The Examination Whilst t he Royal Colleges are w orking t ow ards a unif ied M RCS examinat ion, t his is not yet in place. The Royal Colleges t heref ore have diff ering examinat ion f ormat s. Crit ical care is not specif ically included in t he clinical sect ion of t he examinat ions, t heref ore t his is not discussed. As w it h all examinat ions, t he f ormat may change and candidat es are advised t o check t he lat est regulat ions w it h t he relevant college. England – M RCS Tw o M CQ Papers: Core and Syst ems. Each paper consist s of 65 M CQs and 60 EM Qs t o be answ ered in t w o and a half hours. Crit ical care is t est ed principally in Paper 1. M ult iple t rue/f alse M CQs not negat ively marked. Three Viva Voce examinat ions each of 20 minut es: Anat omy, Physiology and Pat hology. 10 minut es of Basic Science and 10 minut es of Clinical Surgery. Crit ical Care is examined f or 10 minut es in t he physiology viva. Edinburgh – M RCS(Ed) Tw o M CQ Papers: Core Syllabus and Syst ems Syllabus. Negat ively marked. Three Viva Voce examinat ions each of 20 minut es: Crit ical Care, Principles of Surgery, Clinical Surgery & Pat hology. Glasgow – M RCS(Glasg) Tw o M CQ Papers: Core and Syst ems. 2 hours f or each paper. Each paper is a combinat ion of M CQs and EM Qs. M CQs are mult iple t rue/f alse and not negat ively marked. Bot h papers must be sat t he f irst t ime of ent ry. Tw o Viva Voce examinat ions covering: Applied Anat omy, Operat ive Surgery & Principles of Surgery, Surgical Physiology & Crit ical Care and Applied Pat hology & Bact eriology. 30 minut es each divided int o t he t w o sect ions. Crit ical Care f orms a major part of t he physiology viva. Ireland – AFRCSI Tw o M CQ Papers: Paper 1 is a Basic Sciences Paper: This is a t rue/f alse paper, w hich is 2 hours long. There are 30 f ive-part quest ions: 10 each in Anat omy, Physiology and Pat hology. This paper w ill be negat ively marked. Paper 2 is t he Clinical Surgery Paper: This is a 2-hour paper consist ing of 24 quest ions w it h 5 st ems in each quest ion. The second paper w ill be non-negat ively marked. M inimum pass rat e is 60% . The Viva Voce examination consists of three 20-minute orals. The subjects are: Principles of Operative Surgery & Surgical Anatomy, Critical Care, vii

Surgical Emergencies & Applied Physiology, Surgical M anagement & Principles of Pat hology. This College expect s candidat es t o have a high level of know ledge of basic sciences. Theref ore, each of t hese orals w ill include basic science examiners. Each marked out of 100, minimum t o pass 180 out of 300. There are a number of convent ional t erms applied t o t he examinat ions. These are out lined below : Charact erist ic, predominant ly, reliably Typically, f requent ly, commonly, usually Of t en, t ends t o

The f eat ure is present in more t han 90% of cases The f eat ure is present in more t han 60% of cases The f eat ure is present in more t han 30% of cases

Similarly, f or percent ages, a precise f igure (e.g. 2.5% ) means exact ly t hat , w hereas a round f igure (e.g. 20% ) allow s a lit t le eit her w ay (⫾5% ). As w it h all examinat ions, read the question properly.

viii

List of Abbreviations ABC ABE ABG ACE ADH AF AHF AIS ALI ALS AP APACHE APTT ARDS ARF ATN AXR

Airw ay, Breat hing and Circulat ion Act ual base excess Art erial blood gas Angiot ensin convert ing enzyme Ant i-diuret ic hormone At rial f ibrillat ion Acut e hepat ic f ailure Abbreviat ed injury score Acut e lung injury Advanced lif e support Ant ero-post erior Acut e physiology and chronic healt h evaluat ion Act ivat ed part ial t hromboplast in t ime Adult respirat ory dist ress syndrome Acut e renal f ailure Acut e t ubular necrosis Abdominal X-ray

BAE BLS BM I BM R BSD BUN

Bronchial art ery embolisat ion Basic lif e support Body mass index Basal met abolic rat e Brainst em deat h Blood urea nit rogen

CABG CC CKM B CM V CNS CO COHb COPD CPAP CPB CPP CSF CT CVP CVS CXR

Coronary art ery bypass graf t ing Closing capacit y Creat inine kinase M B isoenzyme Cont rolled mandat ory vent ilat ion/Cyt omegalo virus Cent ral nervous syst em Cardiac out put Carboxyhaemoglobin Chronic obst ruct ive pulmonary disease Cont inuous posit ive airw ay pressure Cardiopulmonary bypass Cerebral perf usion pressure Cerebrospinal f luid Comput ed t omography Cent ral venous pressure Cardiovascular syst em Chest X-ray

DC DIC DO2

Direct current Disseminat ed int ravascular coagulat ion Oxygen delivery ix

x

DPG DPL DVT

Diphosphoglycerat e Diagnost ic perit oneal lavage Deep vein t hrombosis

EBV ECF ECG EDRF EDTA EEG EJV EM D ERCP ERV ESR ETT

Epst ein-Barr virus Ext racellular f luid Elect rocardiogram Endot helium-derived relaxant f act or Et hylene diamint et raacet ic acid Elect roencephalogram Ext ernal jugular vein Elect romechanical dissociat ion Endoscopic ret rograde cholangio-pancreat ogram Expirat ory reserve volume Eryt hrocyt e sediment at ion rat e Endo-t racheal t ube

FBC FDP FES FEV FFP FRC FVC

Full blood count Fibrin degradat ion product Fat embolism syndrome Forced expirat ory volume Fresh f rozen plasma Funct ional residual capacit y Forced vit al capacit y

GCS GFR GIT GTN

Glasgow coma score Glomerular f ilt rat ion rat e Gast roint est inal t ract Glyceryl t rinit rat e

HDU HIV HPV HR

High dependency unit Human immunodef iciency virus Hypoxic pulmonary vasoconst rict ion Heart rat e

IABP IAH IAP ICF ICP ICU IJV IL INR IOP IPPV IRV ISS

Int ra-aort ic balloon pump Int ra-abdominal hypert ension Int ra-abdominal pressure Int racellular f luid Int ra-cranial pressure Int ensive care unit Int ernal jugular vein Int erleukin Int ernat ional normalised rat io Int ra-opt ic pressure Int ermit t ent posit ive pressure vent ilat ion Inspirat ory reserve volume/Inverse rat io vent ilat ion Injury severit y scale

ITU IVC

Int ensive t herapy unit Inf erior vena cava

JVP

Jugular venous pressure

LD LDH LFT LM A LOC LOS

Let hal dose Lact at e dehydrogenase Liver f unct ion t est Laryngeal mask airw ay Loss of consciousness Low er oesophageal sphinct er

M AP M AWP M BP MI M ODS M OF M OFS M RI MV

M ean art erial pressure M ean airw ay pressure M ean blood pressure M yocardial inf arct ion M ult i-organ dysf unct ion syndrome M ult i-organ f ailure M ult i-organ f ailure syndrome M agnet ic resonance imaging M inut e volume

NO NSAIDs

Nit ric oxide Non-st eroidal ant i-inf lammat ory drugs

ODC ODP

Oxyhaemoglobin dissociat ion curve Operat ing depart ment pract ioner

PAF PAFC PAH PAOP PAWP PCA PCV PE PEA PEEP PEFR PEG PEJ PIFR PS PSV PT PVR

Plat elet act ivat ing f act or Pulmonary art ery f loat at ion cat het er Para-amino hippuric acid Pulmonary art ery occlusion pressure Peak airw ay pressure Pat ient cont rolled analgesia Pressure cont rolled vent ilat ion Pulmonary embolism Pulseless elect rical act ivit y Posit ive end expirat ory pressure Peak expirat ory f low rat e Percut aneous gast rost omy Percut aneous jejunost omy Peak inspirat ory f low rat e Pressure support Pressure support vent ilat ion Prot hrombin t ime Pulmonary vascular resist ance xi

xii

RAA RBC RDS RQ RR RTS RV

Renin-angiot ensin-aldost erone Red blood cell Respirat ory dist ress syndrome Respirat ory quot ient Respirat ory rat e Revised t rauma score Residual volume

SBC SBE SCV SDH SIADH SIM V SIRS SV SVC SVR

St andard bicarbonat e St andard base excess Subclavicular vein Subdural haemat oma Syndrome of inappropriat e ant idiuret ic hormone Synchronised int ermit t ent mandat ory vent ilat ion Syst emic inf lammat ory response syndrome St roke volume Superior vena cava Syst emic vascular resist ance

TBSA TIAE TIPSS TLC TNF TOE TPN TRALI TT TTE

Tot al body surf ace area Tracheo-innominat e art ery erosion Transjugular int rahepat ic port osyst emic shunt Tot al lung capacit y Tumour necrosis f act or Transoesophageal echo/echocardiogram/echocardiography Tot al parent eral nut rit ion/ Triphosphopyridine nucleot ide Transf usion relat ed acut e lung injury Thrombin t ime Transt horacic echo

U&E

Urea & Elect rolyt es

VC VF VSD VT

Vit al capacit y Vent ricular f ibrillat ion Vent ricular sept al def ect Vent ricular t achycardia

WCC

Whit e cell count

Acknowledgements We w ish t o t hank our f amilies f or t heir cont inuing support , and Gavin Smit h of Greenw ich M edical M edia f or his pat ience and encouragement in seeing t he book t hrough t o press.

xiii

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Section 1 – MCQs Cardiovascular Syst em – Quest ions ..............................................................3 Respirat ory Syst em – Quest ions ..................................................................21 Ot her Syst ems and M ult isyst em Failure – Quest ions ................................36 Problems in Int ensive Care – Quest ions......................................................52 Principles of Int ensive Care – Quest ions ....................................................55 Pract ical Procedures – Quest ions ................................................................61 Cardiovascular Syst em – Answ ers................................................................63 Respirat ory Syst em – Answ ers ....................................................................90 Ot her Syst ems and M ult isyst em Failure – Answ ers..................................111 Problems in Int ensive Care – Answ ers ......................................................130 Principles of Int ensive Care – Answ ers......................................................133 Pract ical Procedures – Answ ers ................................................................140

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Cardiovascular System Q 1.

Quest ions

Concerning the post-operative cardiac surgical patient: A. Vent ricular t achycardia (VT) is common B. Temporary pacing is t he t reat ment of choice f or persist ing bradyarrhyt hmias C. A loop diuret ic (e.g. f urosemide) is t he next line of t reat ment f ollow ing an adequat e f luid load in a pat ient w it h low urine out put D. The incidence of discret e cent ral nervous syst em (CNS) damage is about 2% E. Slow recovery of cent ral t emperat ure is suggest ive of poor cardiac out put (CO)

Q 2.

Concerning cardiopulmonary bypass (CPB): A. The opt imal perf usion pressure is 120 mmHg B. Venous cannulat ion is normally int o t he inf erior vena cava f or closed procedures C. The art erial cannula is usually insert ed in t he descending aort a D. The f emoral art ery is a recognised sit e f or insert ing t he art erial cannula E. The pat ient is cooled t o 25⬚C if circulat ory arrest is necessary

Q 3.

The following are commonly seen after coronary artery bypass grafting (CABG): A. At rial arrhyt hmias B. Basal lung collapse C. Blood loss of approximat ely 250 ml in t he f irst hour af t er surgery D. New Q w aves on elect rocardiogram (ECG) E. Diff use cerebral injury result ing in an alt erat ion in short t erm memory

M CQs

Key Quest ions in Surgical Crit ical Care

3

Q 4.

Causes of poor cardiac output following cardiac surgery include:

Cardiovascular System

A. B. C. D. E. Q 5.

The following are indicators of poor peripheral perfusion: A. B. C. D. E.

Q 6.

Poor myocardial f unct ion Cardiac t amponade Bleeding Hypocapnia Alkalosis

Hypert hermia Oliguria Conf usion M et abolic alkalosis Cent ral cyanosis

Heparin:

Quest ions

A. Increases f ormat ion of Ant it hrombin III – Thrombin complex B. Has a high lipid solubilit y C. Is met abolised in t he liver D. M ay be used in t he t reat ment of disseminat ed int ravascular coagulat ion (DIC) E. M ay lead t o hypot ension Q 7.

Pulmonary artery catheterisation: A. Placement can be conf irmed by a charact erist ic w avef orm B. Sepsis f ollow ing cat het erisat ion may lead t o endocardit is C. Is usef ul in sept ic shock D. Wedging of t he cat het er is necessary in pulmonary inf arct ion E. Cannot be done via peripheral veins

Q 8.

Norepinephrine (noradrenaline): A. Act s mainly by ␣-1 adrenocept ors B. Is excret ed in t he urine C. Has a half lif e of approximat ely 2 minut es

4

M CQs

Key Quest ions in Surgical Crit ical Care

D. Reduces renal blood f low E. M ay increase pulmonary vascular resist ance

Dopamine: A. At low er doses (⬍10 mcg/kg/min) increases cont ract ilit y and heart rat e (HR) B. Can increase cyclic AM P C. Has predominant ly ␤-1 eff ect s at higher doses (⬎10 mcg/kg/min) D. Is more arrhyt hmogenic t han epinephrine (adrenaline) E. Vasodilat es mesent eric vessels

Q 10. Concerning shock:

Quest ions

A. Pulmonary art ery occlusion pressure (PAOP) is usually increased in sept ic shock B. Cardiac out put is of t en decreased in hypovolaemic shock C. Eff ect ive management of shock necessit at es measurement s of bot h cardiac out put and syst emic vascular resist ance D. Blood pressure f alls in sept ic shock E. A urine out put of 15 ml/hr is charact erist ic of class 1 shock

Cardiovascular System

Q 9.

Q 11. Concerning emboli: A. 80% of syst emic art erial emboli originat e f rom t he heart B. 10 ml of gas inject ed is usually suff icient t o cause signif icant problems C. Small pulmonary emboli can lead t o right heart f ailure D. Hypoxia 24 hours af t er a long bone f ract ure is likely t o be due t o pulmonary embolus E. Aort ic t hromboemboli usually have an impact in t he cerebral art erial syst em Q 12. Concerning vascular trauma: A. Haemodynamic inst abilit y is an indicat ion f or urgent angiography B. Cont rast comput ed t omography (CT) is usef ul f or assessing great vessel injury C. Int imal injuries are t he most common vascular injuries

M CQs

Key Quest ions in Surgical Crit ical Care

5

D. Shunt ing may be necessary f or damage cont rol E. Packing is usef ul in cont rolling major art erial bleeds

Cardiovascular System

Q 13. Transfusion: A. Transf usion relat ed acut e lung injury (TRALI) manif est s it self classically by severe dyspnoea B. Graf t versus host disease usually occurs w it hin 24 hours C. M anagement of WBC mediat ed t ransf usion react ions include t he immediat e cessat ion of t he t ransf usion D. Leucodeplet ion reduces t he risk of f ebrile react ions E. M assive t ransf usion is def ined as t he t ransf usion of more t han half t he blood volume in 24 hours

Q 14. Haemorrhagic shock:

Quest ions

A. In class II shock t he syst olic BP is low B. Class III shock is associat ed w it h a urine out put of approximat ely 10 ml per hour C. Pulse pressure is decreased in class I shock D. Class III shock is a loss of approximat ely 25% of t he blood volume E. Conf usion is indicat ive of class III shock

Q 15. The following are causes of peri-operative arrhythmias: A. B. C. D. E.

Hypocapnia Hypoxaemia Pain M yocardial inf arct ion (M I) Local anaest het ics

Q 16. The following ECG changes are supportive for the diagnosis of post-operative pulmonary embolus: A. B. C. D. E. 6

M CQs

Right bundle branch block T w ave inversion in t he ant erior chest leads Lef t axis deviat ion At rial f ibrillat ion (AF) Right vent ricular st rain

Key Quest ions in Surgical Crit ical Care

Q 17. The following haematological parameters would raise the suspicion of DIC: Decreased plat elet s Increased f ibrinogen Prolonged t hrombin t ime Decreased f ibrin degradat ion product s (FDP) Prof use bleeding

Q 18. Concerning intravenous fluids in the critically ill: A. Approximat ely 20% of inf used normal saline (0.9% NaCl) remains int ravascular B. Hart mann’s solut ion (Ringer’s lact at e) cont ains approximat ely 20 mmol/l pot assium C. Normal saline has a pH of 7.4 D. Hart mann’s solut ion is isot onic E. Approximat ely 30% of inf used 5% dext rose remains int ravascular

Quest ions

Q 19. Concerning the post-operative cardiac surgical patient:

Cardiovascular System

A. B. C. D. E.

A. VT is common B. Temporary pacing is generally t he t reat ment of choice f or persist ing bradyarrhyt hmias C. A loop diuret ic (e.g. Furosemide) is t he second line of t reat ment , af t er ensuring adequat e f luid load, f or low urine out put D. The incidence of discret e CNS damage is approximat ely 2% E. Slow recovery of cent ral t emperat ure is suggest ive of poor cardiac out put

Q 20. The following are commonly seen after CABG: A. B. C. D. E.

M CQs

At rial arrhyt hmias Basal lung collapse Blood loss of 250 ml in t he f irst post -operat ive hour New Q w aves on ECG Diff use cerebral injury leading t o short t erm memory alt erat ion

Key Quest ions in Surgical Crit ical Care

7

Q 21. Causes of poor cardiac output following cardiac surgery include:

Cardiovascular System

A. B. C. D. E.

Poor myocardial f unct ion Cardiac t amponade Bleeding Hypocapnia Alkalosis

Q 22. Insertion of a pulmonary artery floatation catheter (PAFC) enables the following: A. B. C. D. E.

M easurement M easurement M easurement M easurement M easurement

of of of of of

right side cardiac f illing pressure lef t side cardiac f illing pressure pulmonary art ery pressure cardiac out put core blood t emperat ure

Quest ions

Q 23. The following may cause pulseless electrical activity (PEA): A. B. C. D. E.

Hypokalaemia Hypocalcaemia Open pneumot horax Cardiac rupt ure ␤-blockers

Q 24. Dopamine: A. B. C. D. E.

St imulat es cardiac ␤-1 recept ors Has a most common complicat ion of t achycardia When it ext ravasat es causes prof ound t issue damage In low doses reduces serum prolact in M ay w orsen mesent eric perf usion at low doses

Q 25. In septic shock: A. Treat ment should be w it h f luid t herapy init ially B. Pulmonary art ery f loat at ion cat het er is cont ra-indicat ed C. Vasoact ive agent s can be usef ul

8

M CQs

Key Quest ions in Surgical Crit ical Care

D. Norepinephrine does not improve renal f unct ion E. 10% of pat ient s present w it h myocardial dysf unct ion

A. Is t he volume of blood eject ed f rom t he lef t vent ricle per minut e B. Is proport ional t o st roke volume (SV) C. Is inversely relat ed t o heart rat e D. Decreases as t he f illing pressure (preload) increases E. Decreases as t he syst emic vascular resist ance (af t erload) increases Q 27. The following statements regarding the circulation are correct:

Quest ions

A. The t ot al blood volume is about 5 lit res B. Only about 50% of t he int ravascular volume is dist ribut ed in t he syst emic art erial circulat ion C. Blood pressure ⫽ cardiac out put ⫻ t ot al peripheral resist ance D. In t he normal heart , t he blood volume is t he main det erminant of cent ral venous pressure (CVP) E. A drop in blood pressure result s in a ref lex increase in heart rat e and vasoconst rict ion mediat ed by barocept ors in t he aort a and carot id sinus

Cardiovascular System

Q 26. Cardiac output:

Q 28. Preload (filling pressure): A. B. C. D. E.

Is dependent upon volume st at us Is reduced by venodilat ors Is reduced by diuret ics Of t he right heart can be measured by t he CVP Of t he lef t heart can be measured by t he PAOP

Q 29. Afterload: A. B. C. D. E.

M CQs

Is t he myocardial w all t ension developed during syst ole Is inversely proport ional t o peripheral vascular resist ance Reduct ion decreases myocardial oxygen requirement s Reduct ion can increase t he st roke volume Reduct ion may increase coronary blood f low

Key Quest ions in Surgical Crit ical Care

9

Q 30. Tissue oxygen delivery increases with:

Cardiovascular System

A. B. C. D. E.

Cardiac out put Haemoglobin concent rat ion Haemoglobin sat urat ion Acidosis Pyrexia

Q 31. Myocardial contractility is reduced by: A. B. C. D. E.

Epinephrine (adrenaline) Hypoxia Dobut amine Nit rat es ␤-blockers

Q 32. Physiological responses to heart failure include:

Quest ions

A. An increase in heart rat e due t o act ivat ion of t he parasympat het ic nervous syst em B. Act ivat ion of t he renin-angiot ensin-aldost erone (RAA) syst em C. Increased eryt hropoiet in secret ion D. Peripheral vasodilat at ion E. Increased sodium and w at er excret ion Q 33. Cardiac failure: A. M ay be def ined as t he f ailure of t he heart t o meet t he met abolic demands of t he body at normal f illing pressures B. Is init ially part ially compensat ed t hrough increased myocardial muscle pre-st ret ching and myocardial cont ract ilit y (St arling’s law ) C. Is most commonly caused by ischaemic heart disease in West ern societ ies D. Is usually associat ed w it h a low syst emic vascular resist ance E. Is usually associat ed w it h a low PAOP Q 34. The CVP is typically elevated in: A. Hypovolaemia B. Congest ive cardiac f ailure

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M CQs

Key Quest ions in Surgical Crit ical Care

C. The f irst 6 hours af t er a general anaest het ic D. Sepsis E. Cardiac t amponade

A. Allow s assessment of t he preload/f illing pressure of t he lef t heart B. Carries a higher risk of pneumot horax by t he subclavian compared w it h t he int ernal jugular approach C. Carries a higher risk of haemot horax by t he subclavian compared w it h t he int ernal jugular approach D. Indicat es hypovolaemia w hen t he CVP is low E. M ay not ref lect t he lef t heart f illing pressure in pat ient s w it h chronic obst ruct ive pulmonary disease (COPD)

Cardiovascular System

Q 35. CVP monitoring:

Q 36. PAOP:

Quest ions

A. Is a ref lect ion of lef t at rial pressure B. Is measured by t emporary occlusion of a pulmonary vein by a f lot at ion cat het er C. M ust be measured in a cardiac cat het er laborat ory D. M easurement may be complicat ed by haemopt ysis E. M easurement may be complicat ed by pulmonary inf arct ion Q 37. PAOP: A. Can be derived f rom t he CVP and haemoglobin concent rat ion B. M easurement involves passage of a pulmonary art ery cat het er across t he int erat rial sept um C. M easurement is appropriat e w hen volume st at us is uncert ain af t er clinical assessment and measurement of t he CVP D. Is t ypically raised in adult respirat ory dist ress syndrome (ARDS) E. Is t ypically raised in sept ic shock Q 38. Quantitative measurement of cardiac output can be made using: A. CVP and haemoglobin concent rat ion B. Thermodilut ion t echniques

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C. An oesophageal Doppler probe D. The Fick principle E. M ixed venous oxygen sat urat ion and heart rat e

Cardiovascular System

Q 39. The following are normal values: A. B. C. D. E.

CVP: 1–10 mmHg PAOP: 16–28 mmHg Cardiac index: 2.5–4 l/min/m 2 Syst emic vascular resist ance: 350–750 dyn s/cm 5 Pulmonary art ery pressure: 25/10 mmHg

Q 40. Cardiogenic shock:

Quest ions

A. Is shock due t o inabilit y of t he heart t o maint ain t he circulat ion B. Is charact erised by a low cardiac out put C. Is charact erised by a low PAOP D. Is charact erised by a low syst emic vascular resist ance E. M ay be caused by papillary muscle rupt ure Q 41. Septic shock is characterised by: A. B. C. D. E.

Increased capillary permeabilit y Vasoconst rict ion A low cardiac out put A high syst emic vascular resist ance A high capillary art ery occlusion pressure

Q 42. On the ECG: A. B. C. D. E.

The P w ave represent s vent ricular depolarisat ion The P w ave occurs during syst ole The QRS complex represent s vent ricular depolarisat ion The T w ave represent s vent ricular repolarisat ion Prolongat ion of t he PR int erval ref lect s delayed conduct ion t hrough t he at riovent ricular node

Q 43. ST segment depression on the ECG may be caused by: A. Lef t vent ricular hypert rophy B. Digoxin t herapy 12

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C. M yocardial ischaemia D. Hyperkalaemia E. Lef t bundle branch block

A. B. C. D. E.

Lef t bundle branch block Complet e heart block ST segment elevat ion ST segment depression Normal ECG

Q 45. In post-operative MI:

Quest ions

A. Creat inine kinase M B isoenzyme (CKM B) is t he most specif ic marker of ischaemic myocardial injury B. Cardiac monit oring is mandat ory C. ST segment elevat ion indicat es t he need f or immediat e administ rat ion of t hrombolyt ic t herapy D. Aspirin should be administ ered E. Int ravenous nit rat es improve prognosis

Cardiovascular System

Q 44. MI may be associated with the following ECG features:

Q 46. Post-myocardial infarction ventricular septal defect (VSD): A. B. C. D.

Causes a diast olic murmur M ay be conf used clinically w it h mit ral regurgit at ion Causes a lef t t o right shunt Is usually diagnosed by t ransoesophageal echocardiogram (TOE) E. Is an indicat ion f or insert ion of an int ra-aort ic balloon pump (IABP)

Q 47. The following are consistent with pulmonary embolism (PE): A. B. C. D. E.

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Raised jugular venous pressure (JVP) Type I respirat ory f ailure Normal ECG PEA Dilat ed right vent ricle on ECG

Key Quest ions in Surgical Crit ical Care

13

Q 48. Risk of post-operative PE is increased by:

Cardiovascular System

A. B. C. D. E.

Pelvic surgery Anaemia Hip surgery M alignancy Renal f ailure

Q 49. Post-operative pulmonary oedema: A. M ay be non-cardiogenic B. M ay be caused by M I in t he absence of chest pain C. Should init ially be t reat ed w it h no more t han 24% oxygen t o avoid t he development of hypercapnia D. Is appropriat ely t reat ed w it h int ravenous opiat e E. Is a recognised cause of t ype I respirat ory f ailure

Quest ions

Q 50. The treatment of acute pulmonary oedema should include: A. B. C. D. E.

24% oxygen ␤-blockers Int ravenous diuret ic Int ravenous nit rat e Angiot ensin convert ing enzyme (ACE) inhibit ors

Q 51. Hypotension in the post-operative patient may be caused by: A. B. C. D. E.

Hypovolaemia Hyperkalaemia PE Urinary ret ent ion Sepsis

Q 52. Hypotension after cardiac surgery may be caused by: A. B. C. D. E. 14

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Cardiac t amponade Lef t vent ricular dysf unct ion Complet e heart block Hypovolaemia Syst emic inf lammat ory response syndrome (SIRS)

Key Quest ions in Surgical Crit ical Care

Q 53. AF after cardiac surgery:

Q 54. The treatment of post-operative AF may include: A. B. C. D. E.

Correct ion of elect rolyt e imbalance Vent ricular rat e cont rol w it h digoxin Pharmacological cardioversion w it h amiodarone Synchronised direct current (DC) cardioversion Ant icoagulat ion

A. B. C. D. E.

Complet e heart block Endocardit is SIRS Cardiac t amponade Neurocognit ive impairment

Quest ions

Q 55. Early complications of aortic valve replacement include:

Cardiovascular System

A. Occurs in 20–40% pat ient s B. Is more common in older pat ient s C. Is charact erised by regular P w ave act ivit y but irregular QRS complexes on t he ECG D. Is usually persist ent unt il elect rical or chemical cardioversion is perf ormed E. Usually indicat es t he occurrence of peri-operat ive M I

Q 56. Signs of cardiac tamponade after cardiac surgery include: A. B. C. D. E.

Hypert ension Raised CVP Kussmaul’s sign Corrigan’s sign Pulsus alt ernans

Q 57. Pericardiocentesis: A. B. C. D. E.

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Is only indicat ed f or cardiac t amponade Is cont ra-indicat ed by malignant disease Is most commonly perf ormed by an apical approach M ay be complicat ed by coronary art ery lacerat ion M ay be complicat ed by lacerat ion of t he right vent ricle

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15

Q 58. Aortic root abscess:

Cardiovascular System

A. M ay cause complet e heart block B. M ay cause f irst degree heart block C. M ay cause persist ent pyrexia despit e appropriat e ant ibiot ic t herapy D. Is a cont ra-indicat ion t o aort ic valve replacement E. Is usually diagnosed by t ranst horacic echo Q 59. Indications for surgery in endocarditis include: A. Haemodynamic compromise due t o valve dysf unct ion B. Penicillin allergy C. Failure t o eradicat e inf ect ion despit e appropriat e ant ibiot ic t herapy D. Recurrent t hromboembolic event s E. Uncomplicat ed nat ive valve endocardit is w it hout haemodynamic compromise

Quest ions

Q 60. Aortic dissection: A. Is predisposed by an inherent w eakness of t he aort ic w all advent it ia B. Is associat ed w it h M arf an’s syndrome C. Is associat ed w it h hypert ension D. Is associat ed w it h pregnancy E. Is classif ied as St anf ord t ype B w hen t he ascending aort a is involved Q 61. Aortic dissection: A. B. C. D. E.

M ay cause mit ral regurgit at ion M ay cause renal f ailure M ay cause inf erior M I M ay cause pleural but not pericardial eff usion M ay cause acut e low er limb ischaemia

Q 62. In aortic dissection: A. M agnet ic resonance imaging (M RI) is t he invest igat ion of choice f or unst able pat ient s B. Echocardiography is able t o assess aort ic root size, presence of aort ic regurgit at ion and pericardial eff usion 16

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Q 63. TOE: A. Is cont ra-indicat ed in t he int ubat ed pat ient B. Requires monit oring of pat ient oxygen sat urat ion and heart rhyt hm C. Has a sensit ivit y and specif icit y of about 95% f or t he diagnosis of aort ic dissect ion D. Can be used int raoperat ively t o monit or lef t vent ricular f unct ion E. Is indicat ed t o assess t he int ra-operat ive result s of mit ral valve repair

A. Is a posit ive inot rope B. St imulat es ␤-1, ␤-2, and ␣-1 recept ors C. Causes vasodilat at ion and a decrease in peripheral vascular resist ance D. Is indicat ed in t he t reat ment of cardiogenic shock E. Result s in a low er increase in myocardial oxygen requirement s t han ot her inot ropes

Quest ions

Q 64. Dobutamine:

Cardiovascular System

C. Int ravenous labet alol is appropriat e ant ihypert ensive t herapy D. Dist al dissect ions should generally be managed surgically E. Surgical t reat ment is cont ra-indicat ed w hen t he ascending aort a is involved

Q 65. Epinephrine (adrenaline): A. B. C. D.

St imulat es bot h ␣- and ␤-adrenocept ors Causes vasodilat at ion and a decrease in af t erload Reduces myocardial oxygen demand Increases coronary and cerebral perf usion during cardiopulmonary resuscit at ion E. Can be given via an endot racheal t ube during a cardiac arrest Q 66. The following statements are correct: A. Norepinephrine (noradrenaline) predominant ly st imulat es ␤-adrenocept ors B. Norepinephrine is a pot ent vasoconst rict or

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Cardiovascular System

C. Norepinephrine is indicat ed in t he t reat ment of shock associat ed w it h a low peripheral vascular resist ance D. Dopamine is t he precursor of epinephrine and norepinephrine E. Dopamine independent ly improves out come in acut e renal f ailure Q 67. IABP: A. Should be posit ioned w it h t he t ip of t he balloon proximal t o t he lef t subclavian art ery B. Is t imed t o inf lat e during syst ole C. Increases coronary perf usion pressure D. Increases af t erload E. Requires ant icoagulat ion Q 68. IABP:

Quest ions

A. Is indicat ed in acut e mit ral regurgit at ion due t o papillary muscle rupt ure B. Is indicat ed in acut e severe aort ic regurgit at ion C. Is indicat ed in aort ic dissect ion D. M ay be complicat ed by low er limb ischaemia E. M ay be complicat ed by pericardial eff usion Q 69. In out-of-hospital suspected cardiac arrest: A. The f irst considerat ion is minimising risk t o rescuer and vict im B. The airw ay should be opened by ‘head t ilt /chin lif t ’ C. The vict im’s breat hing should be assessed f or 30 seconds bef ore init iat ing rescue breat hing D. The unconscious self -vent ilat ing vict im should be placed in t he recovery posit ion E. Chest compression should be init iat ed if t here are no signs of a circulat ion af t er a 10 second assessment Q 70. In basic life support (BLS): A. A rat io of 15 chest compressions t o t w o rescue breat hs should be used B. Chest compressions achieve about 50% normal cardiac out put

18

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Q 71. In pulseless ventricular tachycardia/ventricular fibrillation (VT/VF): A. BLS carries a 20% chance of rest oring an eff ect ive cardiac rhyt hm B. A praecordial t hump may rest ore a cardiac out put C. The chance of successf ul def ibrillat ion decreases by 10% per minut e D. The recommended energy sequence f or t he f irst t hree successive def ibrillat ions is 200 J, 300 J, 360 J E. Lidocaine (lignocaine) is t he ant iarrhyt hmic drug of choice f or shock-resist ant VT/VF

A. Cerebral hypoxic injury begins w it hin 3 minut es B. Drug delivery is opt imally achieved via a cent ral vein C. Epinephrine (adrenaline) 1 mg should be administ ered every minut e during cardiopulmonary resuscit at ion D. Open chest cardiac massage is indicat ed af t er recent cardiot horacic surgery E. Associat ed w it h t rauma, t he cervical spine should be prot ect ed during airw ay manipulat ion

Quest ions

Q 72. In cardiac arrest:

Cardiovascular System

C. Chest compressions should be perf ormed at a rat e of 70 per minut e D. Chest compression should depress t he st ernum by 10 cm E. Chest compressions should be int errupt ed f or each rescue breat h

Q 73. In cardiac arrest, drugs that can be administered down the endotracheal tube include: A. B. C. D. E.

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Amiodarone Sodium bicarbonat e At ropine Calcium gluconat e Lidocaine (lignocaine)

Key Quest ions in Surgical Crit ical Care

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Q 74. PEA:

Cardiovascular System

A. Is charact erised by cardiac arrest w it h an ECG rhyt hm ot her t han VT compat ible w it h a cardiac out put B. M ay be caused by t ension pneumot horax C. M ay be caused by hypovolaemia D. Should be t reat ed w it h 3 mg at ropine irrespect ive of heart rat e E. Should be t reat ed w it h epinephrine (adrenaline) 1 mg every 3 minut es of cardiopulmonary resuscit at ion

Quest ions

20

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Respiratory System Q 1.

Positive end expiratory pressure (PEEP): A. B. C. D. E.

Q 2.

Hypovolaemia Oedema Renal f ailure Syndrome of inappropriat e ant idiuret ic hormone (SIADH) Diuret ics

The following are clinical manifestations of barotrauma: A. B. C. D. E.

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Respirat ory rat e (RR) ⬎ 30 breat hs per minut e Oxygen sat urat ion ⬍ 90% PaO2 ⬍ 8 kPa PaCO2 ⬍ 7 kPa Dyspnoea

Hyponatraemia may be due to: A. B. C. D. E.

Q 4.

Increases f unct ional residual capacit y (FRC) Decreases lung compliance Increases int ra-cranial pressure Increases lung barot rauma M ay increase cardiac out put (CO)

The following are indicators of failure of mask oxygen therapy at high FIO2: A. B. C. D. E.

Q 3.

Quest ions

Pneumot horax Pneumomediast inum Subcut aneous emphysema Pneumoperit oneum Air embolus

Key Quest ions in Surgical Crit ical Care

21

Q 5.

The following may cause respiratory alkalosis:

Respiratory System

A. B. C. D. E. Q 6.

Hypot hyroidism Fever Pain Anaemia Pregnancy

Adult respiratory distress syndrome (ARDS): A. Is charact erised by pulmonary oedema in t he presence of a raised pulmonary art ery occlusion pressure (PAOP) B. M ay be caused by acut e pancreat it is C. M ay be caused by sept icaemia D. M ay complicat e cardio-pulmonary bypass E. Is managed w it h st eroids, w hich improve prognosis

Q 7.

Post-operative respiratory failure may be caused by:

Quest ions

A. B. C. D. E.

Q 8.

Central chemoreceptors: A. B. C. D. E.

Q 9.

ARDS Aspirat ion pneumonia Basal at elect asis Opiat e analgesia Pulmonary embolism

Det ect t he level of O2 and CO2 in blood Are direct ly st imulat ed by CO2 Buff ering capacit y in cerebrospinal f luid (CSF) is good CO2 diff uses slow ly bet w een CSF ⫹ blood Normal cont rol of vent ilat ion is mediat ed by CO2 homeost asis

Control of ventilation: A. Peripheral chemorecept ors are sensit ive t o O2 and are locat ed in t he carot id and aort ic sinus B. Out put f rom peripheral chemorecept ors st art t o increase at PaO2 13.3 kPa and st op below PaO2 4.4 kPa C. Concomit ant increase in CO2 pot ent iat es t he eff ect of hypoxia but t he response is linear above 5.3 kPa

22

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D. Cent ral chemorecept ors are sit uat ed on t he dorsal medulla oblongat e and t halamus E. The Hering-Breuer ref lex is concerned w it h lung inf lat ion, t he impulses f or w hich are carried w it hin t he vagus nerve

A. Tot al lung capacit y is t he maximal volume of air t hat can be expired f ollow ing a maximal inspirat ion B. Tidal volume is 8–12 ml/kg in adult s C. Expirat ory reserve volume is t he maximal volume of air t hat can be expelled af t er t idal expirat ion, and is usually over 3000 ml D. Closing capacit y is t he lung volume w here small air w ay begin t o collapse on inspirat ion E. In f it adult s at alt it ude t ot al lung capacit y and vit al capacit y are equal

Respiratory System

Q 10. The following statements refer to lung volumes:

Q 11. FRC: Quest ions

A. Is t he volume of air remaining in t he lungs af t er a maximal expirat ion B. Is usually great er t han inspirat ory reserve volume C. When less t han closing capacit y result s in hypoxaemia during t idal vent ilat ion D. Is increased by cont inuous posit ive airw ays pressure (CPAP) E. Is increased by regional anaest hesia Q 12. Compliance: A. Is t he rat e of change of gas f low per unit change in pressure ⌬f /⌬p B. Is a measurement of lung dist ensibilit y C. Is increased in t he new born D. Is decreased in rest rict ive lung disease E. Is increased at low lung volumes Q 13. Ventilation and perfusion: A. During spont aneous respirat ion t he majorit y of inspired gas is direct ed t o t he upper part s of t he lung B. Upper part s of t he lung are on a st eeper part of t he compliance curve in spont aneously breat hing pat ient s

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Respiratory System

C. Blood f low is great est at t he base of t he lung due t o t he eff ect s of hydrost at ic pressure D. Alt ering t he mode of vent ilat ion f rom spont aneous t o mechanical has minimal eff ect on vent ilat ion perf usion rat io in t he supine subject E. Hypoxic pulmonary vasoconst rict ion (HPV) is a met hod w hereby t he lungs decrease t he blood supply t o t he lungs Q 14. Ventilation and perfusion:

Quest ions

A. Shunt ref ers t o areas of t he lung w hich are w ell vent ilat ed but w it h poor blood supply B. Dead space ref ers t o areas of t he lung w hich are w ell perf used but poorly vent ilat ed C. Pat ient s w it h hypoxaemia due t o shunt w ill benef it f rom 100% O2 delivered via a f acemask t o increase haemoglobin sat urat ion D. Physiological shunt account s f or about 2% of CO E. Upper areas of t he lung t end t ow ards shunt rat her t han dead space during mechanical vent ilat ion Q 15. Pulmonary function tests: A. FEV1/FVC rat io is usually of t he order of 0.6 B. FEV1/FVC rat ios are more helpf ul in demonst rat ing obst ruct ive rat her t han rest rict ive lung pat hologies C. In rest rict ive condit ions FEV1 and FVC are bot h reduced but t he rat io is of t en increased D. In obst ruct ive condit ions FEV1 remains const ant but t he FVC is of t en increased E. FVC and FEV1 are usually measured at t he bedside w it h a peak f low met er Q 16. Arterial blood gases (ABG): A. PaCO2 of 4.6 kPa is w it hin t he normal range B. pH is direct ly proport ional t o t he H⫹ cont ent of blood C. St andard bicarbonat e (SBC) is a direct measurement of plasma bicarbonat e D. Decreasing t he t emperat ure of a sample decreases t he H⫹ cont ent E. Decreasing t he t emperat ure of a sample decreases t he O2 cont ent

24

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Q 17. Acid-base homeostasis:

Q 18. Metabolic Acidosis:

Q 19. pH 7.1, PCO2 2.8 kPa, PO2 13 kPa, HCOⴚ 3 7 mmol/l, SBC 8 mmol/l, actual base excess (ABE) ⴚ 21 mmol/l, standard base excess (SBE) ⴚ 20 mmol/l, Glucose 22 mmol/l. Which of the following are true for this patient:

Quest ions

A. Can be due t o int est inal f ist ulae B. Is of t en t he result of acid ingest ion (iat rogenic) C. Pat ient s should be given sodium bicarbonat e t o correct any def icit D. M ay be compounded by hypervent ilat ion E. M ay result f rom salicylat e ingest ion

Respiratory System

A. The cells of t he human body can f unct ion over a w ide-range of pH values B. An open buff er syst em is one in w hich t here is an inexhaust ible supply of component s C. Haemoglobin is a more eff ect ive buff er in t he oxygenat e HbO f orm D. Haemoglobin and plasma prot eins account f or nearly half t he body’s buff ering capacit y E. Fully compensat ed acidosis may result in a pH value of 7.46

A. NaHCO3 8.4% 100 ml should be given as soon as possible B. The primary problem is due t o loss of HCO⫺ 3 f rom t he body C. Cont rolling blood sugar is a primary concern and should be t he f irst priorit y D. The pat ient may require 10 lit res of int ravenous f luid E. This pat ient may be oliguric Q 20. pH 7.56, PCO2 7.2 kPa, PO2 9 kPa, HCOⴚ 3 45 mmol/l, SBC 35 mmol/l, ABE 10 mmol/l, SBE 6 mmol/l, Sat 90%. Which of the following are true for this patient: A. B. C. D. E.

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This pat ient may be t aking diuret ics Hypoxia may be secondary Treat ment opt ions include normal saline inf usion The urine pH w ill be about 6 They may have Conn’s syndrome

Key Quest ions in Surgical Crit ical Care

25

Q 21. Respiratory acidosis:

Respiratory System

A. Caused by ast hma is usually self limit ing B. Is not of primary concern in mult i-t rauma vict ims w ho may have many ot her injuries C. Normal pH may be achieved saf ely w it h small amount s of sodium bicarbonat e D. Despit e compensat ion a pat ient w it h pH 7.38 may st ill have a PaCO2 of 8 kPa E. The bicarbonat e buff er syst em is not usef ul since t he mechanism f or CO2 removal may be impaired Q 22. Respiratory alkalosis:

Quest ions

A. When caused by salicylat e poisoning is associat ed w it h met abolic acidosis B. Occurs w it h pneumonia C. Oxygen t herapy should be avoided init ially unt il t he diagnosis of cause is made D. When occurring in pat ient s w it h deep vein t hrombosis (DVT) is usually clinically irrelevant E. M ay result in t he pat ient passing urine of pH 5.5 Q 23. Regarding oxygen delivery: A. Is more eff icient at Hb 10 g/dl t han 15 g/dl B. Is decreased at alt it ude due t o reduced CO C. Increasing t he inspired oxygen concent rat ion t o 50% increases t he oxygen cont ent of blood by 50% D. A pat ient w it h Hb 10 g/dl breat hing air w ill have great er oxygen delivery t han a pat ient w it h Hb 8 g/dl breat hing 50% O2 E. The dissolved f ract ion of O2 cont ribut es upt o 10% of t he t ot al oxygen carrying capacit y Q 24. Hypoxia: A. B. C. D. E.

26

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Carbon monoxide poisoning causes hist ot oxic hypoxia St agnant hypoxia responds w ell t o oxygen t herapy Alt it ude result s in anaemic hypoxia St agnant hypoxia leads t o low venous oxygen cont ent Cyanot ic heart disease is a cause of hypoxic hypoxia

Key Quest ions in Surgical Crit ical Care

Q 25. Oxygen therapy:

Q 26. Oxygen therapy:

Quest ions

A. Vent uri masks are examples of f ixed perf ormance oxygen delivery syst ems B. Oxygen concent rat ion is independent of peak inspirat ory f low rat e (PIFR) but not minut e volume C. Red masks deliver 40% oxygen at 10 l/min D. Is less usef ul t han Hudson mask in COPD pat ient s since t hey t end t o deliver higher concent rat ions of oxygen E. Require more oxygen f low (l/min) t o reach t he same oxygen concent rat ion t han t he equivalent Hudson mask

Respiratory System

A. St ops shivering in post -operat ive pat ient s by reducing t he met abolic demand f or oxygen B. The oxygen concent rat ion delivered by t he Hudson mask may be accurat ely derived f rom t he f resh gas f low C. At higher peak inspirat ory f low rat es (PIFR) t he oxygen concent rat ion is increased because more air is ent rained D. The maximal oxygen concent rat ion t hat can be delivered by nasal specs is 40% E. 10 l/min via t he Hudson mask gives an oxygen concent rat ion of over 80%

Q 27. Respiratory failure: A. B. C. D. E.

Type I t here is ↓ PaO2 and ↓ or normal PaCO2 Type II t here is normal PaO2 but ↑ PaCO2 Type I may be due t o pneumonia Type I is associat ed w it h Guillain Barré syndrome Type I is associat ed w it h ARDS

Q 28. Respiratory failure: A. Type II f ailure is easier t o t reat t han t ype I B. Kyphoscoliosis usually produces respirat ory f ailure w it hout elevat ion in PaCO2 C. Type II f ailure is not associat ed w it h t achypnoea D. Flail chest result s in t ype I f ailure since CO2 is lost t o t he at mosphere via an open pneumot horax E. M echanical obst ruct ion of t he airw ay is associat ed w it h t ype I f ailure

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27

Q 29. The following are reliable signs of respiratory failure:

Respiratory System

A. B. C. D. E.

Cyanosis Low ered level of consciousness Tachypnoea Tachycardia Use of accessory muscles of respirat ion

Q 30. The following are indications for instituting respiratory support: A. B. C. D. E.

PaO2 ⬍ 8 kPa breat hing 10 l/min O2 via a vent uri mask Tidal volume (Vt ) ⬍ 5 ml/kg Glasgow coma score (GCS) of 10 PaCO2 ⬎ 7 kPa Int ra-operat ive t racheost omy f ormat ion

Q 31. Intermittent positive pressure ventilation (IPPV): Quest ions

A. Diff ers f rom spont aneous vent ilat ion in t hat expirat ion is act ive B. Can lead t o acid/base dist urbances C. Pneumot horacies should not be drained prior t o inst it ut ing IPPV since t he result ing air leak makes vent ilat ion ineff icient D. M ay w orsen shunt leading t o hypoxaemia E. M ay cause an init ial increase in blood pressure Q 32. IPPV: A. B. C. D. E.

Reduces cardiac out put (CO) Seldom requires sedat ion unless t he pat ient is anxious M ay reduce blood pressure on correct ion of acidosis Has no eff ect on t he kidney M ay increase int ra-cranial pressure

Q 33. Initiating IPPV: A. FIO2 should be set t o 1.0 (100% Oxygen) B. Tidal volume (Vt ) should be 6–8 ml/kg C. Oxygen is mixed w it h nit rous oxide t o prevent pulmonary at elect asis in t he int ensive care unit (ICU) D. The I:E rat io is of t en ext ended t o 1:3 in ast hmat ic pat ient s E. PEEP should be applied as soon as possible 28

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Q 34. Controlled mandatory ventilation (CMV): M inut e volume is set on t he vent ilat or RR depends on t he pat ient ’s inspirat ory eff ort Peak pressure is cont rolled by t he vent ilat or Is usef ul f or pat ient s w it h poor respirat ory compliance Is not a w eaning mode

Q 35. Synchronised intermittent mandatory ventilation (SIMV):

Q 36. Pressure controlled ventilation (PCV): A. B. C. D. E.

Quest ions

A. M inut e volume is not const ant B. M ay result in spont aneous and mandat ory breat hs being delivered simult aneously result ing in dangerously high peak airw ay pressures C. M uscle relaxat ion is usually required t o minimise increases in peak airw ay pressure D. Is a w eaning mode E. Improves perf usion and vent ilat ion mat ching over cont rolled mandat ory vent ilat ion (CM V)

Respiratory System

A. B. C. D. E.

Is f avoured w hen pulmonary compliance is high Is a w eaning mode The square w ave pressure t race opt imises oxygenat ion Volume and RR are set on t he vent ilat or M uscle relaxat ion is usually required

Q 37. Pressure support ventilation (PSV): A. B. C. D. E.

Requires no sedat ion Is a w eaning mode M uscle relaxat ion is occasionally required Tidal volume is set on t he vent ilat or RR depends on vent ilat or and pat ient init iat ed breat hs

Q 38. The following are mechanisms for optimising lung volume: A. PEEP is mainly used during spont aneous vent ilat ion B. CPAP is a w eaning mode

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C. Bot h PEEP and CPAP improve haemodynamic st abilit y by increasing diast olic blood pressure D. Inverse rat io vent ilat ion (IRV) involves act ive expirat ion E. IRV may lead t o respirat ory acidosis

Respiratory System

Q 39. Weaning from mechanical ventilation: A. Opioids should be discont inued B. Should not be rout inely at t empt ed f rom PCV C. Pat ient s should be put ont o a T-piece once t he SIM V rat e has been reduced t o 8 breat hs per minut e D. Pat ient s should be put ont o a T-piece once t he PEEP level is 10 cmH2O E. Once a pat ient has been put on t o T-piece spont aneous vent ilat ion t hey should not go back ont o PSV on a vent ilat or

Q 40. Endo-tracheal intubation: Quest ions

A. The correct diamet er f or a paediat ric endo-t racheal t ube (ETT) is det ermined by t he f ormula Age/2 ⫹ 12 B. The correct diamet er f or an adult ETT is 9 mm f or males C. The correct lengt h f or an adult ETT is 25 cm f or f emales D. Sellicks manouvre aims t o aid int ubat ion E. Cricoid pressure should be applied w it h a f orce of 40 N Q 41. Airway: A. Nasal int ubat ion is less cardio vascularly st imulat ing t han oral because laryngoscopy is not required B. Nasal int ubat ion is f avoured in children C. Nasal int ubat ion is more uncomf ort able and requires more sedat ion t han oral D. Int ubat ion is mandat ory if GCS ⬍ 8 E. Tracheost omy is more suit able t o vent ilat e obese pat ient s Q 42. ARDS: A. M ay occur af t er cardio-pulmonary bypass B. Is know n t o be associat ed w it h malignant hypert ension C. A high plasma amylase concent rat ion may be seen

30

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Key Quest ions in Surgical Crit ical Care

D. Is caused by raised int ra-cranial pressure E. Inf ect ion is t he commonest cause Q 43. The following criteria must be met to define ARDS:

Q 44. ARDS:

Quest ions

A. Has a similar pat hophysiology t o t he syst emic inf lammat ory response syndrome (SIRS) B. M icrovascular oblit erat ion is an init iat ing event C. Capillary endot helial damage is cent ral t o t he pat hological process D. A prot ein rice exudat e f ills t he alveoli due t o large hydrost at ic f orces E. A f ibrosing-alveolit is t ype react ion is an early pat hological sign in severe cases

Respiratory System

A. The pulmonary art ery w edge pressure must be great er t han 18 mmHg B. There must be bilat eral f luff y inf ilt rat es on t he chest X-ray (CXR) C. There must be t he need f or mechanical vent ilat ion D. There must be high airw ay pressures E. The PaO2:FIO2 rat io is ⬎27 kPa

Q 45. The management of ARDS: A. Fluids should be given liberally as t here is likely t o be co-exist ing sept icaemia or hypoperf usion t hat requires resuscit at ion B. A pulmonary art ery f lot at ion cat het er should alw ays be insert ed C. Normocapnia should be maint ained t o avoid acidosis D. M oderat e hypoxaemia (PaO2 ⬎ 8 kPa) should be t olerat ed E. Increased peak airw ay pressure has t o be accept ed in order t o reduce CO2 Q 46. The management of ARDS: A. PEEP should not be applied since t he airw ay pressure w ill already be high B. Increasing FRC w ill improve oxygenat ion

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31

C. IRV increases mean airw ay pressure (M AWP) w it hout increase in peak airw ay pressure D. IRV opt imises gas exchange E. Nit ric oxide may be given int ravenously t o help resist ant hypoxia

Respiratory System

Q 47. ARDS: A. B. C. D.

Poly t rauma associat ed w it h ARDS carries a grave prognosis Late deaths from ARDS are often due to the precipitating cause M ost survivors are asympt omat ic 50% of survivors show signs of lung f ibrosis on laborat ory t est ing E. Pneumot horacies, once drained aid vent ilat ion by reducing t he peak airw ay pressure via t he air leak

Q 48. Open pneumothorax: Quest ions

A. Is less clinically signif icant t han closed pneumot horax since pressure in t he lungs equilibrat es w it h at mospheric pressure B. The lung on t he side of a penet rat ing injury does not cont ribut e t o vent ilat ion C. Air exchange occurs bet w een t he collapsed and healt hy lung D. There w ill be no mediast inal shif t since t he aff ect ed lung is open t o t he at mosphere E. There may be bradypnoea t o compensat e f or t he air leak

Q 49. Pneumothorax: A. Closed pneumot horax is relat ively common and may not be clinically signif icant B. In t ension pneumot horax air can only escape via t he bronchial t ree C. In t ension pneumot horax t here may be t racheal deviat ion t ow ards t he collapsed lung D. There may be an increase of 40 mmHg in int rapleural pressure on t he aff ect ed side E. Tension pneumot horax is usually diagnosed by CXR

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Q 50. The following concern CO2 transport in blood:

Q 51. The following relate to the transport of CO2 in blood:

Quest ions

A. Plasma prot eins are signif icant ly involved in t he buff ering of H⫹ liberat ed during t he t ransport of CO2 B. Deoxyhaemoglobin has less buff ering capacit y t han oxyhaemoglobin because of t he low er pH (7.36) of venous blood C. The Haldane eff ect allow s f or great er upt ake of CO2 D. Chloride shif t ref ers t o t he movement of Cl ⫺ out of t he RBC t o allow inw ard movement of HCO⫺ 3 E. RBC in venous blood has less Cl ⫺ t han art erial blood

Respiratory System

A. CO2 is 20 t imes more soluble t han O2 B. CO2 is t ransport ed as HCO⫺ 3 , account ing f or upt o 50% of carriage in blood C. HCO⫺ 3 is mainly buff ered by plasma prot eins D. Carbamino compounds are mainly f ormed w it h plasma prot eins E. 70% of HCO⫺ 3 f ormed f rom CO2 in t he red blood cell (RBC) diff uses int o t he plasma

Q 52. Oxygen transport in blood: A. Haemoglobin in a complex carbohydrat e of 65,000 Dalt ons B. There are f our haem cont aining subgroups, each being a complex of perphyrin and Fe3⫹ C. The oxygen dissociat ion curve is sigmoid because of t he diff ering aff init ies of t he haem groups t o O2 D. 1 g Hb can carry 1.38 ml of O2 E. Increasing Hb f rom 12 g/dl t o 15 g/dl has lit t le eff ect in increasing t he oxygen carrying capacit y unless t he PaO2 is also increased

Q 53. Oxyhaemoglobin dissociation curve (ODC): A. Lef t shif t increases t he slope of t he curve B. Right shif t increases t he aff init y of Hb f or O2 C. The Bohr eff ect is most prominent in t he lungs

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33

D. Increasing t emperat ure reduces t he aff init y of Hb f or O2 E. 2,3-Diphosphoglycerat e (2,3-DPG) generat ed by RBC glycolysis binds avidly t o oxyhaemoglobin

Respiratory System

Q 54. ODC: A. M ixed venous sat urat ion corresponds t o P50 B. M et haemoglobin is f ormed w hen f errous iron in Hb is reduced t o t he f erric f orm C. M yoglobin has a non-sigmoid dissociat ion curve because of it s great er aff init y f or O2 D. Fet al Hb gives up O2 more easily t han adult Hb, w hich improves t issue oxygenat ion at low PaO2 E. Carbon monoxide dissociat ion curve is t o t he lef t of myoglobin

Q 55. Oxygen toxicity: Quest ions

A. Is rare if PIO2 (part ial pressure of inspired oxygen) is less t han 60 kPa B. Hyperoxia increases surf act ant levels in a bid t o keep t he airw ays open C. Is usually asympt omat ic and painless unt il loss of consciousness D. Inf ant s are less suscept ible since t hey cannot increase surf act ant levels easily E. M ay occur during diving

Q 56. Surface tension in the alveoli: A. Is def ined by Laplace’s law B. The w all t ension is inversely proport ional t o t he t ransmural pressure C. Gas t ends t o f low f rom large radius alveoli t o smaller radius alveoli t o equilibrat e t he pressure D. Surf act ant , a phospholipid prevent s, airw ay collapse by increasing surf ace t ension in smaller alveoli E. Surf act ant is produced by t ype II alveolar cells

34

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Q 57. The following statements refer to dead space:

Respiratory System

A. Anat omical dead space is 5 ml/kg B. Physiological dead space consist s of anat omical dead space minus alveolar dead space C. Alveolar dead space corresponds t o t hose part s of t he lung w hich are vent ilat ed but not perf used D. Physiological dead space may be measured using Fow ler’s nit rogen w ashout met hod E. Alveolar dead space may be est imat ed using t he Bohr equat ion

Quest ions

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35

Other Systems and Multisystem Failure Q 1.

The following are indicators of a severe attack acute pancreatitis: A. B. C. D. E.

Q 2.

Plasma calcium ⬎ 2.6 mmol/l Art erial pO2 ⬍ 8 kPa Amylase ⬎ t hree t imes upper limit of laborat ory norm Blood glucose ⬎ 8 mmol/l Whit e cell count (WCC) ⬎ 15 ⫻ 109/l

The following are factors which increase risk of rebleeding following a gastrointestinal haemorrhage: A. B. C. D. E.

Q 3.

Quest ions

M alignancy Acut e rat her t han chronic ulcer Shock on admission Age ⬍ 60 years Gast ric ulcer

Concerning severe pancreatitis: A. Hypocalcaemia is t he most common met abolic problem B. Coagulopat hy is usually t he f irst organ syst em f ailure t o manif est it self C. Failure of t w o organ syst ems is associat ed w it h 90% mort alit y D. Solid, inf ect ed pancreat ic necrosis w ill of t en respond t o int ravenous ant ibiot ics E. Posit ive end expirat ory pressure (PEEP) may be usef ul in managing respirat ory f ailure

Q 4.

Concerning acute renal failure (ARF): A. Ult rasound should be perf ormed early B. Supravesical obst ruct ion is common C. Insert ion of a double J st ent is t he pref erred t reat ment of supravesical obst ruct ion

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Q 5.

Concerning thoracic trauma: A. Chest t rauma is responsible f or approximat ely 25% of t rauma deat hs B. M ost pat ient s w it h chest injuries ult imat ely require t horacot omy C. Penet rat ing chest w ounds of t en require f ormal surgery ut ilising cardiopulmonary bypass D. M assive haemot horax is def ined as ⬎750 ml blood in t he chest cavit y E. Cont inuing blood loss of ⬎50 ml/h is an indicat ion f or t horacot omy Characteristic injuries of blunt thoracic trauma include: A. B. C. D. E.

Q 7.

Causes of hypoxia in thoracic trauma include: A. B. C. D. E.

Q 8.

Blood loss Cardiac t amponade Pulmonary cont usion Vent ilat ory f ailure M ediast inal disrupt ion

The following drugs require dose alteration in renal failure: A. B. C. D. E.

M CQs

Fract ured st ernum Transect ed aort a Pulmonary cont usion Rupt ured spleen Bilat eral rib f ract ures

Quest ions

Q 6.

Other Systems and Multisystem Failure

D. A unilat eral dilat ed collect ing duct syst em requires urgent decompression and subsequent renography E. For pelvic malignancy causing ARF nephrost omy insert ion is t he t reat ment of choice

Paracet amol Heparin M orphine Ranit idine M et oclopramide

Key Quest ions in Surgical Crit ical Care

37

Other Systems and Multisystem Failure

Q 9.

Subdural haematoma (SDH): A. Is associat ed w it h a 20% mort alit y in cases of simple SDH B. Follow ing decompression, management is aimed at decreasing cerebral sw elling C. M ult iple SDH is associat ed w it h a mort alit y as high as 90% D. Is due t o t he t earing of bridging vessels E. Is classically associat ed w it h a lucid int erval

Q 10. Concerning shock after a spinal injury: A. Absent ref lexes suggest spinal shock B. Hypot ension and t achycardia suggest neurogenic shock C. Tachycardia and f laccid muscle is common in spinal shock D. Bradycardia is a f eat ure of spinal shock E. Vasopressors may be required in neurogenic shock

Quest ions

Q 11. Concerning smoke inhalation injuries: A. The half lif e of carboxyhaemoglobin (COHb) breat hing 100% oxygen is less t han 1 h B. High f low oxygen should be given unt il t he COHb level is less t han 5% C. Smoke inhalat ion causes t hermal damage t o t he w hole respirat ory t ract D. Soot in t he mout h is an indicat ion f or f ibre-opt ic laryngoscopy E. Int ubat ion should be avoided

Q 12. Gastrointestinal stress ulceration: A. B. C. D.

Is rare Causes signif icant bleeds in 5% of cases Has a mort alit y w hich is inf luenced by prophylaxis Can be prevent ed by t he use on H2 ant agonist s in all crit ically ill pat ient s E. Of t en necessit at es surgical int ervent ion

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A. B. C. D. E.

Small bow el obst ruct ion Inf lammat ory bow el disease Dysphagia Small bow el f ist ulae Diarrhoea

Q 14. The following are necessary daily for patients on total parenteral nutrition (TPN): A. B. C. D. E.

Full blood count (FBC) Albumin Calcium Urea Glucose

A. Rect al examinat ion is of t en unnecessary B. The pat ient should have a uret hral cat het er insert ed in all cases t o monit or urine out put C. Ant ero-post erior (AP) compression injuries are usually more severe t han lat eral compression injuries D. Pelvic st abilisat ion is t he f irst priorit y E. Unst able pelvic ring f ract ures are associat ed w it h a high mort alit y

Quest ions

Q 15. Concerning clinical evaluation of pelvic injuries:

Other Systems and Multisystem Failure

Q 13. Enteral nutrition is contra-indicated in the following circumstances in the critically ill patient:

Q 16. Concerning thermal regulation: A. Hypert hermia is def ined as a body t emperat ure above 39⬚C B. Respirat ory acidosis occurs w it h hypert hermia C. M alignant hyperpyrexia is relat ed t o t he use of volat ile anaest het ic agent s D. The nervous syst em is most of t en aff ect ed in hypert hermia E. Cent ral lines should be changed at 5 day int ervals

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39

Other Systems and Multisystem Failure

Q 17. Anastamotic leakage:

Quest ions

Q 19. The following criteria allow for non-operative management of liver injuries:

A. B. C. D. E.

Is uncommon Has a higher incidence in shocked pat ient s When suspect ed merit s an early 2nd look procedure There is no role f or CT scanning Early nut rit ional support is advisable

Q 18. Concerning the cephalosporins: A. Cef uroxime is a 3rd generat ion cephalosporin B. Approximat ely 25% of pat ient s w it h penicillin hypersensit ivit y are also hypersensit ive t o t he cephalosporins C. They have variable int est inal absorpt ion D. They are generally met abolised in t he liver E. 3rd generat ion cephalosporins are less act ive against gram-posit ive organisms t han 2nd generat ion

A. B. C. D. E.

Haemodynamically st able pat ient Persist ent abdominal pain Blood t ransf usion requirement of 2 unit s Int ra-hepat ic haemat oma on CT scan Haemoperit oneum ⬍1 l on CT scan

Q 20. The following are indications for laparotomy in abdominal trauma: A. B. C. D. E.

Perit onit is Persist ent shock Eviscerat ion Uncont rolled haemorrhage Gunshot w ounds

Q 21. The following are recognised post-operative complications following hepato-biliary surgery for trauma: A. Rebleeding B. Bile leaks usually requiring f urt her surgery C. Ischaemic segment s 40

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Key Quest ions in Surgical Crit ical Care

Q 22. Concerning mortality after liver injury: A. B. C. D.

The overall mort alit y is approximat ely 25% Penet rat ing injury carries a mort alit y of 15–20% Blunt injury has a low er mort alit y t han penet rat ing injury M ort alit y of blunt hepat ic injury is approximat ely 10% if only t he liver is injured E. Bleeding causes t he majorit y of deat hs Q 23. Blunt trauma to the pancreas: A. M ay be clinically occult B. Abdominal radiographs may show ret roperit oneal air C. Endoscopic ret rograde cholangio-pancreat ogram (ERCP) is t he best invest igat ion D. Serum amylase is a good invest igat ion E. Duct damage may be missed at laparot omy

A. B. C. D. E.

Quest ions

Q 24. The following complications are associated with pancreatic trauma:

Other Systems and Multisystem Failure

D. Subhepat ic sepsis in approximat ely 20% of cases E. Inf ect ed f luid collect ions rarely

Pseudocyst Pancreat ic f ist ula Ascit es Pancreat ic abscess Acut e pancreat it is

Q 25. The post-operative hepatic transplant patient: A. B. C. D.

Should resume ent eral f eeding as soon as possible St eroids are usually cont inued f or at least 1 year Liver f unct ion t est s (LFTs) are perf ormed daily Cyclosporin is of t en given in combinat ion w it h azat hioprine as immunosuppressive E. Acut e reject ion occurs in approximat ely half t he pat ient s Q 26. The following are contra-indications to liver transplantation: A. Hepat ocellular carcinoma B. Ext rahepat ic malignancy

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41

Other Systems and Multisystem Failure

C. Syst emic sepsis D. Liver met ast ases f rom sarcomat a E. Cardiopulmonary disease

Q 27. Acute renal failure: A. Carries a mort alit y of approximat ely 10% B. Oliguria in an adult is def ined as a urine out put less t han 400 ml per day C. M ort alit y increases t o 70% if one ot her organ syst em is involved D. Sequelae include hypercalcaemia and hypokalaemia E. M ay lead t o pericardit is

Q 28. The following may cause post-operative hepatic dysfunction:

Quest ions

A. B. C. D. E.

Sepsis Pancreat it is Transf usion Hypoxia Surgery

Q 29. The following are major inflammatory mediators in systemic inflammatory response syndrome (SIRS): A. B. C. D. E.

Plat elet act ivat ing f act or (PAF) Tumour necrosis f act or (TNF) ␤ Int erleukin 1 Int erleukin 8 Int erleukin 5

Q 30. The following endocrine responses occur after major trauma: A. B. C. D. E. 42

M CQs

Increased prolact in Decreased ant i-diuret ic hormone (ADH) Increased t hyroxine Increased cat echolamines Increased cort isol

Key Quest ions in Surgical Crit ical Care

A. B. C. D. E.

Ampicillin Cef uroxime Benzyl penicillin Gent amicin M et ronidazole

Q 32. Regarding head injury:

Q 33. The following are radiological signs of major thoracic trauma: A. B. C. D. E.

Quest ions

A. The mort alit y associat ed w it h an acut e subdural haemat oma is approximat ely double t hat of acut e epidural haemat oma B. Skull f ract ure is associat ed w it h a 20-f old increase in incidence of ext radural haemat oma C. Pat ient s w it h acut e subdural haemat oma may have a lucid int erval D. Rapid decelerat ion injuries are associat ed w it h subdural haemat oma E. Cont recoup injuries are of t en more serious t han coup injuries

Other Systems and Multisystem Failure

Q 31. In patients with renal failure, dose modification may be necessary with the following antibiotics:

M ediast inal w idening Fract ured 2nd rib Fract ured st ernum M ediast inal emphysema Loss of aort ic def init ion

Q 34. Concerning enteral nutrition in the ICU patient: A. Where int ra-cranial pressure (ICP) is elevat ed sodium rest rict ed f eeds are appropriat e B. High volume energy dense f eeds are used f or pat ient s w it h severe burns C. Glut amine supplement at ion is essent ial t o prevent skelet al muscle cat abolism D. A t ypical 2000 ml f eed w ould provide approximat ely 35 g prot ein E. 100 ml of st andard polymeric ent eral f eed provides approximat ely 100 kcal energy

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43

Other Systems and Multisystem Failure

Q 35. The following are complications of enteral nutrition:

Quest ions

Q 37. Concerning head injuries:

A. B. C. D. E.

Aspirat ion Hypoglycaemia Hypercapnia Fluid overload Inf ect ion

Q 36. Concerning ballistic thoracic injuries: A. Wit nessed cardiac arrest is an indicat ion f or resuscit at ive t horacot omy B. Pneumot horax is t he commonest injury C. 80% of pat ient s w it h a haemot horax can be t reat ed w it h t ube t horacost omy alone D. Pericardiocent esis is of limit ed value E. Explorat ory t horacot omy is t he t reat ment of choice f or t ransmediast inal injuries

A. Epidural haemat oma classically present w it h a lucid int erval B. Acut e SDH have a bet t er prognosis t han epidural haemat oma C. M aint enance of cerebral perf usion pressure (CPP) is essent ial in t heir management D. ICP is normally 15–25 mmHg in an adult E. CPP should be maint ained above 60 mmHg Q 38. Treatment of raised ICP includes: A. B. C. D. E.

CSF drainage Prophylact ic hypervent ilat ion Int ravenous 20% mannit ol Sedat ion Hypot hermia

Q 39. The following monitoring is necessary in cases of acute cervical spinal cord injury: A. Art erial blood pressure B. Pulmonary art ery occlusion pressure C. End-t idal CO2 44

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Key Quest ions in Surgical Crit ical Care

Q 40. Burns: A. M ort alit y associat ed w it h a concomit ant inhalat ion injury is 30% great er t han t hat w it hout inhalat e injury B. Inhalat ion injury commonly result s in hypoxaemia associat ed w it h bronchospasm and bronchorrhoea C. Burn w ound sepsis is t he leading cause of deat h D. The hypermet abolic response t o burn injury peaks at 48 h E. Burns pat ient s suff er a marked prot ein cat abolism

Q 41. The following are indications for surgery in acute pancreatitis: Posit ive f ine needle aspirat e Sepsis Perit onit is Failure t o respond t o ICU t herapy Respirat ory insuff iciency

Quest ions

A. B. C. D. E.

Other Systems and Multisystem Failure

D. Pulse oximet ry E. Urinary out put

Q 42. The following are suggestive of pre-renal renal failure: A. B. C. D. E.

Urine sodium ⬍ 20 mmol/l Urine osmolalit y ⬎ 500 mosm/kg H2O Fract ional excret ion of sodium ⬎ 1% Urine creat inine/plasma creat inine ⬍ 20 M uddy brow n granular cast s

Q 43. Fluid balance: A. A 70 kg man has approximat ely 28 l f luid in t he int erst it ial compart ment B. Approximat ely 95% pot assium is ext racellular C. The daily requirement of sodium is 1–2 mmol/kg/day D. Hart mann’s solut ion is pref erred t o normal saline in pat ient s w it h renal f ailure E. The st ress response t o surgery leads t o sodium ret ent ion

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45

Other Systems and Multisystem Failure

Q 44. Fat embolism: A. Leads t o t he f at embolism syndrome (FES) in 20% of cases B. Is f requent ly seen in pat ient s w it h acut e pancreat it is C. Occurs in associat ion w it h reaming of long bones D. Necessit at es heparinisat ion E. Requires management by vent ilat ion Q 45. Characteristics of the FES include: A. B. C. D. E.

Pulmonary insuff iciency Thrombocyt osis Conjunct ival haemorrhages Pet echial rash Cerebral signs

Q 46. Causes of hypoxia in thoracic trauma include:

Quest ions

A. B. C. D. E.

Blood loss Tamponade Pulmonary cont usion Vent ilat ory f ailure M ediast inal disrupt ion

Q 47. Clearance of the following drugs is reduced in ICU patients with hepatic dysfunction: A. B. C. D. E.

M idazolam Fent anyl Diazepam Thiopent one Furosemide (f rusemide)

Q 48. The following are risk factors for the development of acute tubular necrosis (ATN): A. B. C. D. E. 46

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Diabet es mellit us Inf ect ion M alnut rit ion Hypovolaemia Increasing age

Key Quest ions in Surgical Crit ical Care

A. B. C. D. E.

Cephalosporins M orphine Dext ran Cot rimoxazole Benzyl penicillin

Q 50. The following would be indications to transfer a patient to a burns centre: A. B. C. D.

Chemical burns 15% 2nd degree burns in a pat ient aged 60 10% burns in an 8 year old boy An elect rical burn w it h an ent ry w ound on t he f inger and t he pat ient unable t o f lex t he f inger E. 10% 3rd degree burns t o t he chest in a 25 year old

A. B. C. D. E.

Is charact erised by a normal anion gap Is most commonly caused by poor t issue perf usion M ay be caused by met f ormin Impairs myocardial cont ract ilit y Should usually be t reat ed by t he administ rat ion of sodium bicarbonat e

Quest ions

Q 51. Lactic acidosis:

Other Systems and Multisystem Failure

Q 49. The following drugs may cause ARF:

Q 52. Disseminated intravascular coagulation (DIC) is characterised by: A. B. C. D. E.

Increased f ibrinogen concent rat ion Increased f ibrinogen degradat ion product s Prolonged act ivat ed part ial t hromboplast in t ime (APTT) Thrombocyt haemia Fragment ed red cells on blood f ilm

Q 53. DIC may be caused by: A. Gram-negat ive sept icaemia B. M yocardial inf arct ion C. Burns

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47

Other Systems and Multisystem Failure

D. Pulmonary embolism E. Haemolyt ic blood t ransf usion react ions

Q 54. pH 7.27, pCO2 3.7 kPa, pO2 12.6 kPa, HCO3 14 mmol/l, base excess – 10 mmol/l (on air). These arterial blood gases are characteristic of: A. B. C. D. E.

Respirat ory acidosis Respirat ory f ailure Acut e renal f ailure Sept ic shock Lact ic acidosis t ype A

Q 55. pH 7.27, pCO2 7.9 kPa, pO2 7.1 kPa, HCO3 24 mmol/l, base excess 2 mmol/l (on air). These arterial blood gases are characteristic of:

Quest ions

A. B. C. D. E.

Type I respirat ory f ailure Chronic CO2 ret ent ion Opiat e t oxicit y Acut e lif e-t hreat ening ast hma Benzodiazepine overdose

Q 56. SIRS: A. M ay be precipit at ed by t umour invasion B. M ay result f rom acut e hypoxaemia post -operat ively C. Is less likely in burns vict ims since t hey have a reduced immune response D. Is due primarily t o an abnormal immune react ion E. Usually result s in mult i-organ dysf unct ion syndrome (M ODS)

Q 57. SIRS may be diagnosed by: A. B. C. D. E. 48

M CQs

Peripheral t emperat ure ⬎ 38.5o C Core t emperat ure of 35.8o C Tachycardia of 95 beat s per minut e Respirat ory alkalosis w it h a PaCO2 of 4.2 kPa WCC of 3.9 x 109/l (w it h 11% neut rophils)

Key Quest ions in Surgical Crit ical Care

A. B. C. D.

Can occur w it hout act ive inject ion Result s in cool peripheries due t o syst olic hypot ension Can result in respirat ory acidosis due t o hypoperf usion The pat ient may have deranged clot t ing due t o liver hypoperf usion E. Hypot ension is exaccerbat ed by nit ric oxide mediat ed vasodilat at ion Q 59. Multi-organ dysfunction syndrome: A. Is a direct eff ect of end-organ inf lammat ion B. Oliguria is a lat e sign suggest ing t hat organ f ailure has occurred C. Gut hypoperf usion and mucosal at rophy is proposed t o have a role in propagat ing t he inf lammat ory react ion D. Is usually irreversible E. In t he lungs result s in ARDS

A. Fluid t herapy should be used sparingly since t issue oedema and hypoperf usion may be w orsened B. Inot ropes w hich increase af t erload are avoided since t hey can det eriorat e myocardial f unct ion C. There is no place f or ␤ agonist s since t hey exacerbat e peripheral vasodilat at ion D. Invasive measurement of cardiac out put is mandat ory t o guide t reat ment E. Art erial cannulat ion is avoided because of t he risk of dist al ischaemia

Quest ions

Q 60. Management of MODS:

Other Systems and Multisystem Failure

Q 58. SIRS:

Q 61. Prognosis in MOF: A. Is improved in burns pat ient s because t hey are t reat ed in specialist cent res B. M ort alit y rat e is 95% on 4t h day w it h t hree organs f ailed C. M ort alit y rat e is 20% on 1st day w it h t w o organs f ailed D. Is w orse at t he ext remes of age E. Is improved in sepsis since t he inf ect ing precipit ant may be isolat ed, cult ured and t reat ed

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49

Other Systems and Multisystem Failure

Q 62. Electrolyte composition: A. B. C. D. E.

Int racellular K+ concent rat ion is normally ⬎150 mmol/l Ca2+ is almost ent irely ext racellular The daily requirement of Ca2+ is 1 mmol/kg/day M g 2+ is mainly ext racellular Ext racellular HCO⫺ 3 is t hree t imes as concent rat ed as int racellular

Q 63. The following statements concern crystalloid solutions: A. 5% dext rose has a similar osmolalit y t o blood B. Hart mann’s solut ion has equal concent rat ions of Na+ and Cl ⫺ C. Dext rose saline is dist ribut ed equally in int racellular f luid (ICF) and ext racellular f luid (ECF) D. N/saline is hypert onic t o blood E. Hart mann’s solut ion is isot onic t o blood

Quest ions

Q 64. The following are appropriate replacement therapies for the fluid loss: A. B. C. D. E.

Perit onit is and f resh f rozen plasma (FFP) Vomit ing and D/saline Diabet es mellit us and Hart mann’s solut ion Diabet es insipidus and 5% dext rose Burns and blood

Q 65. Nutrition: Body mass index (BM I) is w eight 2/height Normal BM I is 22–28 Nit rogen requirement is usually 9 g/day f or an adult male Energy requirement s are 10–20 kcal/kg f or adult f emales per day E. In cat abolic pat ient s 1g nit rogen should be given f or every 80–100 kcal energy A. B. C. D.

Q 66. Nutrition in organ failure – the following are appropriate: A. Respirat ory disease – low carbohydrat e, high f at B. Renal f ailure – low nit rogen, high f at 50

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Key Quest ions in Surgical Crit ical Care

Q 67. Nutrition – routes of feeding: A. The parent eral rout e is f avoured during acut e phases of illness on ICU since f luid balance is bet t er cont rolled B. Ent eral f eeding of t en requires t he use of mucosal prot ect ion such as sucralf at e, since it is direct ly irrit ant t o t he gast ric lining C. Ent eral f eeding increases t he risk of nosocomial pneumonia D. Hyperglycaemia is only associat ed w it h parent eral nut rit ion in diabet ic pat ient s E. Bow el sounds are a good predict or of gut f unct ion Q 68. Nutrition – physiology:

M CQs

Key Quest ions in Surgical Crit ical Care

Quest ions

A. Fat s and carbohydrat es are complet ely oxidised t o CO2 and w at er in t he body B. Prot ein usually makes up less t han 20% of diet ary int ake C. A high prot ein diet increases met abolic rat e D. Respirat ory quot ient (RQ) f or f at is higher t han carbohydrat e E. Prot ein consumpt ion has a signif icant eff ect on t he overall RQ value

Other Systems and Multisystem Failure

C. Cardiac impairment – low sodium, high volume D. Liver disease – low nit rogen, low carbohydrat e E. Cerebral impairment – low glucose

51

Problems in Intensive Care Q 1.

Quest ions

Concerning brainstem death (BSD): A. Elect roencephalogram (EEG) recording is necessary in t he UK t o conf irm BSD B. 24 hours must elapse bet w een t he f irst and second set of brainst em t est s C. The vest ibulo-ocular ref lex is t est ed by inject ing 5 ml of ice-cold w at er int o each ext ernal audit ory meat us D. Apnoea is t est ed f or by disconnect ing f rom t he vent ilat or and insuff lat ing w it h 6 l/min oxygen unt il PaCO2 ⬎ 6.65 kPa E. Hypot hermia is an exclusion crit eria f or BSD

Q 2.

Concerning post-operative surgical site infections: A. Deep inf ect ions may occur more t han 6 mont hs af t er implant at ion of a prost hesis B. Clean w ounds are associat ed w it h inf ect ion rat es of about 3% C. The most common pat hogen is St aphylococcus aureus D. To reduce w ound inf ect ions t he operat ive sit e should be shaved t he night bef ore surgery E. Lat ex drains reduce t he rat e of inf ect ion f ollow ing abdominal surgery

Q 3.

Fat embolism: A. Is more common af t er open t han closed f ract ures B. Leads t o t he f at embolism syndrome (FES) in 20% of cases C. Is commonly seen in pat ient s w it h severe acut e pancreat it is D. Occurs during t he reaming process of int ramedullary nailing E. Causes hypoxaemia and hypercarbia

52

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Key Quest ions in Surgical Crit ical Care

Q 4.

Characteristics of the FES are:

Q 5.

The following are normal paediatric vital signs: A. B. C. D. E.

Q 6.

Quest ions

Abdominal surgery Ant ibiot ic t reat ment Int ubat ion Diabet es Hypot ension

The following organisms are likely to cause lung infections in the intensive care unit (ICU) in the mentioned circumstances: A. B. C. D. E.

M CQs

Tw o consult ant s EEG Apnoea Absent gag ref lex A minimum of 24 hours bet w een t he t w o set s of t est s

The following are risk factors for nosocomial pneumonia: A. B. C. D. E.

Q 8.

Respirat ory rat e (RR) 40 in a 9 mont h old girl Heart rat e (HR) 120 in a 4 year old girl Syst olic BP 80 mmHg in a 7 year old boy HR 60 in a 10 year old girl Syst olic BP 60 mmHg in a 2 year old boy

The following are required in the UK to confirm BSD: A. B. C. D. E.

Q 7.

Pulmonary insuff iciency Thrombocyt osis Conjunct ival haemorrhages Pet echial rash Cerebral signs

Problems in Intensive Care

A. B. C. D. E.

S. aureus – head injury Pseudomonas aeruginosa – prolonged vent ilat ion Anaerobes – head injury S. aureus – t horacoabdominal surgery Haemophilus inf luenzae – t racheot omy

Key Quest ions in Surgical Crit ical Care

53

Q 9.

In septic shock, the following antibiotics are appropriate for the suspected site of infection:

Problems in Intensive Care

A. B. C. D. E.

GI Tract – clindamycin Surgical w ound – vancomycin Lung – piperacillin Urinary t ract – penicillin Surgical w ound – cef t azidime

Quest ions

54

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Principles of Intensive Care Q 1.

The following score highly (2 or more) on the acute physiology and chronic health evaluation (APACHE) scoring system: A. B. C. D. E.

Q 2.

Epidural opioids are f ive t imes more pot ent t han int ravenous Is associat ed w it h decreased respirat ory complicat ions M ay cause cord compression Urinary ret ent ion occurs in approximat ely 10% Hypot hesia should be t reat ed w it h ephedrine and f luids

The following signs would alert a clinician to consider critical care referral: A. B. C. D. E.

M CQs

Is highly lipid soluble Can be given int rat hecally Is excret ed primarily by t he kidney Has a half lif e of approximat ely 30 minut es Is more likely t han morphine t o produce respirat ory depression

Epidural analgesia: A. B. C. D. E.

Q 4.

Temperat ure more t han 39.2⬚C Respirat ory rat e (RR) 24 breat hs per minut e Heart rat e (HR) 105 beat s per minut e Pot assium 5.4 mmol/l Haemat ocrit 50%

Diamorphine: A. B. C. D. E.

Q 3.

Quest ions

RR ⬎ 30 breat hs per minut e M ean BP 180 mmHg, HR 100 beat s per minut e Glasgow coma score (GCS) 7, Pulse 80, BP 130/80 mmHg RR 8 breat hs per minut e, HR 50 beat s per minut e Temperat ure 37.6⬚C, HR 110 beat s per minut e

Key Quest ions in Surgical Crit ical Care

55

Q 5.

The following factors have been shown to affect outcome in intensive therapy unit (ITU) patients:

Principles of Intensive Care

A. B. C. D. E.

Q 6.

The following analgesics have the physiological effect stated: A. B. C. D. E.

Quest ions

Q 7.

Alf ent anil causes sedat ion M orphine increases bile duct pressure Fent anyl leads t o hist amine release Fent anyl is an ant it ussive M orphine increases splanchnic perf usion

Invasive haemodynamic monitoring may be associated with the following complications: A. B. C. D. E.

Q 8.

Increased age Early diagnosis of t he acut e condit ion Severit y of t he acut e illness Physiological reserve Therapy

M edian nerve neuropat hy Very rarely int ra-art erial t hrombosis Pneumot horax in 10% of cent ral lines Thoracic duct injury demanding surgical int ervent ion Pulmonary art ery rupt ure, during insert ion of a pulmonary art ery f loat at ion cat het er, w it h a mort alit y of 50%

Intensive care unit (ICU) scoring systems: A. Hospit al mort alit y rat e is a usef ul guide t o ICU perf ormance B. Scoring syst ems, can be used t o decide on opt imal t reat ment f or individual pat ient s C. Risk adjust ment is only usually necessary f or mult i-organ pat hology D. Select ion bias may occur due t o incomplet e validat ion of dat a E. Lead-t ime bias t akes account of any t reat ment t hat t he pat ient has had bef ore being admit t ed t o ICU

56

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Q 9.

The revised trauma score (RTS):

Q 10. Scoring systems:

Quest ions

A. APACHE st ands f or adverse pat hology and chronic healt h evaluat ion B. APACHE III is used t o guide t he most st at ist ically successf ul t reat ment C. SAPS II st ands f or simplif ied acut e physiology score and has 17 variables D. APACHE II does not t ake mechanical vent ilat ion int o account E. APACHE II has more predict ive pow er over individual pat ient out come t han SAPS II

Principles of Intensive Care

A. Correlat es w ell w it h risk of mort alit y B. Scores 0–12 by a combinat ion of GCS, mean blood pressure (M BP) and oxygen sat urat ion C. A score of 12 correlat es w it h over 90% mort alit y D. A score of 6 correlat es w it h a 63% survival E. BP 80/50 mmHg scores 3

Q 11. Injury severity scale (ISS): A. The abbreviat ed injury score (AIS) is calculat ed by t he sum of t he squares of t he cat egories of t he ISS B. AIS let hal dose in 50% (LD 50) is age independent provided pat ient s have t he same physiological reserve C. ISS def ines seven anat omical areas D. In t he ISS loss of consciousness f or 12 minut es scores 3 E. In t he ISS biliary t ree injury scores higher t han splenic rupt ure

Q 12. Sedative drugs: A. Thiopent one is a suit able drug f or general sedat ion in t he ICU B. During propof ol inf usion, nut rit ional advice should be sought regarding t riphosphopyridine nucleot ide (TPN) const it ut ion C. Et omidat e causes muscle t w it ching D. Ket amine may be used f or rapid sequence induct ion

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57

E. M idazolam is suit able f or long t erm inf usion since it is highly w at er soluble and does not undergo signif icant hepat ic met abolism

Principles of Intensive Care

Q 13. Sedative drugs: A. Propof ol and et omidat e cause pain on inject ion B. M idazolam is t he drug of choice f or long t erm sedat ion since it has a short durat ion of act ion C. Ket amine causes hallucinat ions D. Propof ol has a durat ion of act ion of 2–3 minut es w hen given by bolus E. Et omidat e does not w ork in one arm-brain circulat ion t ime Q 14. Analgesic drugs:

Quest ions

A. B. C. D. E.

M orphine and f ent anyl have similar eliminat ion half lives M orphine is longer act ing t han f ent anyl Fent anyl is more pot ent t han alf ent anil Alf ent anil has a longer durat ion of act ion t han f ent anyl M orphine prevent s, hist amine release by mast cell st abilisat ion

Q 15. Opioids: A. M ay cause chest w all st iff ness leading t o diff icult y w it h mechanical vent ilat ion B. Sedat ion but not prurit us is reversed by naloxone C. M orphine 3 sulphat e is an act ive met abolit e D. M orphine 6 sulphat e is not an act ive met abolit e E. Cause hypot ension by vasodilat at ion

Q 16. Muscle relaxants: A. Rocuronium is used f or rapid int ubat ion B. At racurium is a st eroid and should not be used in renal f ailure C. Vecuronium may be used in liver f ailure D. Vecuronium given as a bolus w orks w it hin 60 seconds E. At racurium is broken dow n by Hoff mann degradat ion, w hich is t emperat ure dependent 58

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Key Quest ions in Surgical Crit ical Care

Q 17. Suxamethonium: Is st ruct urally relat ed t o acet yl choline Causes signif icant hypokalaemia in burns pat ient s Is met abolised in t he liver Causes myalgia Decreases int ra-opt ic pressure (IOP)

Q 18. Physiology of body fluids: A. Osmolalit y is t he concent rat ion of a solut ion expressed as osmoles of solut e per lit re of solut ion (mosmol/l) B. Osmolarit y is measured by depression of f reezing point C. Toxicit y is t he osmot ic pressure produced by osmot ically act ive part icles at select ive membranes D. Semipermeable membranes allow solut e but not solvent t o pass t hrough E. Osmolalit y of plasma is 290 mosmol/l

A. The kidney is involved in gluconeogenesis B. Each kidney is made up of t w elve t housand nephrons C. Cort ical nephrons have long loops of Henle w hich pass int o t he inner medulla D. Juxt amedullary nephrons account f or less t han 2% of f unct ional unit s and are primarily concerned w it h blood pressure aut oregulat ion E. The out er medulla has t he great est blood f low reaching 625 ml/min during exercise

Quest ions

Q 19. Renal physiology:

Principles of Intensive Care

A. B. C. D. E.

Q 20. Renal physiology: A. Glomerular f ilt rat ion rat e (GFR) is measured by t he Fick principle, using t he subst rat e para-amino hippuric acid (PAH) B. Renal oxygen consumpt ion is large leading t o a low renal venous oxygen cont ent C. The inner medulla is concerned w it h t he count ercurrent exchange mechanism and hence has t he great est oxygen consumpt ion

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59

D. The cort ex ut ilises f at t y acids in oxidat ive met abolism E. The medulla ut ilises glucose in anaerobic met abolism

Principles of Intensive Care

Q 21. Renal physiology: A. Renin is released f rom t he macula densa in t he proximal convolut ed t ubule B. Renin is a prot eolyt ic enzyme exclusive t o t he kidney C. Angiot ensin I is an oct apept ide D. Angiot ensin II exert s posit ive f eedback on t he adrenal cort ex E. Angiot ensin II is act ive in t he cent ral nervous syst em (CNS) Q 22. Drugs and the kidney:

Quest ions

A. Syst emic hypert ension causes a diuresis B. Carbonic anhydrase inhibit ors cause a diuresis w it h low pH and increased ammonia excret ion C. Loop diuret ics inhibit Na⫹ Cl ⫺ co-t ransport in t he descending loop of Henle causing a large diuresis D. Thiozide diuret icis inhibit Ca2⫹ t ransport E. Amiloride is an aldost erone ant agonist w hich reduces K⫹ excret ion in t he dist al convolut ed t ubule

60

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Practical Procedures Q 1.

Quest ions

Regarding vascular access: A. Silicone cat het ers can be t hrombogenic B. Approximat ely 40% of cent ral venous cat het ers become colonised w it h bact eria C. Vascular cat het er relat ed sept icaemia occurs in approximat ely 5% of pat ient s D. The insert ion point f or a subclavian cat het er is at t he junct ion bet w een t he medial 2/3 and t he lat eral 1/3 of t he clavicle E. The f emoral vein lies lat eral t o t he art ery in t he sheat h

Q 2.

Regarding intra-cranial pressure (ICP) monitoring: A. M ore t han 50% of t hose needing operat ive t reat ment of head injuries have rises of ICP more t han 20 mmHg B. ICP ⬎ 40 mmHg is associat ed w it h neurological abnormalit ies C. ICP ⬎ 60 mmHg is unif ormly f at al D. Vent ricular cat het ers or subarachnoid bolt s are of t en used E. ICP monit oring is cont ra-indicat ed in inf ect ion

Q 3.

Complications of tracheotomy: A. Pneumot horax occurs in upt o 5% B. The inf erior jugular vein is most likely t o cause bleeding problems C. Treat ment of t racheo-innominat e art ery erosion (TIAE) requires urgent ligat ion of t he art ery D. M ort alit y of TIAE, t reat ed rapidly is 10% E. Approximat ely 5% of t racheal t ubes are accident ly dislodges

Q 4.

Cricothyroidotomy: A. The ent ry point is t he cricot hyroid membrane, inf erior t o t he cricoid cart ilage B. M ay be surgical or percut aneous

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61

C. Voice changes occur in half t he pat ient s D. Is associat ed w it h subglot t ic st enosis E. As an emergency procedure has double t he complicat ion rat e of an elect ive procedure

Practical Procedures

Q 5.

The following are complications of arterial line insertion: A. B. C. D. E.

Q 6.

False aneurysm Haemat oma Occlusion Air embolus Thrombosis

The following statements concern the internal jugular vein (IJV):

Quest ions

A. Is f ormed at t he jugular bulb and drains blood via t he sigmoid sinus B. St art s it s journey t hrough t he neck ant erior t o t he carot id art ery and ends up lat eral t o it C. It runs a st raight pat h f rom jugular f oramen t o st ernoclavicular joint covered only by carot id sheat h and skin D. Insert ion of cannula int o t he middle t hird is most comf ort able in aw ake pat ient s E. Cannulat ion is less likely t o cause arrhyt hmias t han t he subclavian vein Q 7.

Vascular access – the following statements concern central line insertion: A. In pat ient s w it h head injuries and raised ICP, neut ral or head dow n t ilt should be avoided B. A low approach t o t he IJV reduces t he incidence of side eff ect s C. The subclavian approach is pref erred if t here is risk of bleeding t o avoid haemat oma f ormat ion in t he neck D. Placement inadvert ent ly int o t he ext ernal jugular vein (EJV) may not be recognised unt il t he post procedure CXR E. IJV on t he right side is t he sit e of choice since t here is less risk of major blood vessel erosion

62

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Cardiovascular System A 1.

A. f alse

B. t rue

C. f alse

D. t rue

Answ ers

E. t rue

Vent ricular t achycardia (VT) suggest s eit her peri-operat ive myocardial damage or ongoing myocardial ischaemia. Low urine out put requires f luid loading, t hen dopamine (2 ␮g/kg/min) bef ore a loop diuret ic. SCC pp 49–55

Surgery 1996 14: 4; 78–81

A 2.

A. f alse

B. f alse

C. f alse

D. t rue

E. f alse

The opt imal perf usion pressure is 50–70 mmHg. For open heart surgery t he superior vena cava (SVC) and inf erior vena cava (IVC) are used f or t he venous cannula. For closed procedures it is t he right at rium. The art erial cannula is usually locat ed in t he ascending or proximal arch of t he aort a. Cooling is bet w een 12–18⬚C f or circulat ory arrest . SCC pp 35–37

Surgery 1996 14: 2; 46–48

A 3.

A. t rue

B. t rue

C. f alse

D. f alse

E. t rue

Blood loss should be ⬍100 ml. New Q w aves are indicat ive of a localised myocardial inf arct ion (M I) and occur in ⬍5% . SCC pp 49–55

A 4.

A. t rue

B. t rue

C. t rue

D. f alse

E. f alse

Hypercapnia and acidosis rat her t han t hose st at ed. SCC pp 49–55

Surgery 1996 14: 1; 1–5

A 5.

A. f alse

B. t rue

C. t rue

D. f alse

E. f alse

Hypot hermia, met abolic acidosis and peripheral cyanosis are f eat ures along w it h cool, clammy skin, poor capillary ref ill and a

M CQs

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63

low volume pulse. In ext reme circumst ances, oliguria is in f act anuria. SCC pp 15–20

Cardiovascular System

A 6.

A. t rue

B. f alse

C. t rue

D. t rue

E. t rue

Heparin has low lipid solubilit y and is met abolised in t he liver. The use of heparin in disseminat ed int ravascular coagulat ion (DIC) is cont roversial but does happen. SCC pp 41–46

A 7.

A. t rue

B. t rue

C. t rue

D. f alse

E. f alse

Placement of a pulmonary art ery cat het er can be conf irmed by t he w avef orm along w it h pulmonary art ery w edge pressure being less t han mean pulmonary art ery pressure, f luid f lushing easily w hen w edged, and w edged PaO2 ⬍ mixed venous PaO2.

Answ ers

Wedging is cont ra-indicat ed in cases of pulmonary inf arct ion. The f emoral vein is not uncommonly used f or insert ion of a pulmonary art ery f loat at ion cat het er. SCC pp 18–20, p 214

A 8.

A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Noradrenaline reduces renal blood f low by vasoconst rict ion. SCC pp 7–8

A 9.

A. t rue

B. t rue

C. f alse

D. f alse

E. t rue

Dopamine can increase or decrease cyclic AM P. Alpha eff ect s predominat e at higher doses and it is less arrhyt hmogenic t han epinephrine. SCC pp 6–8

A 10. A. f alse

B. t rue

C. t rue

D. f alse

E. f alse

Pulmonary art ery occlusion pressure is usually decreased in sept ic and hypovolaemic shock and increased in cardiogenic shock. Cardiac out put f alls w it h hypovolaemic and cardiogenic shock and rises in sept ic shock, as does blood pressure. 64

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A urine out put of 15 ml/hr is indicat ive of class 3 shock (blood loss 1.5–2 lit res) SCC p 20, pp 29–32

B. f alse

C. t rue

D. f alse

E. f alse

M ore t han 100 ml of gas needs t o be inject ed t o cause signif icant problems. Fat embolus is much more likely t han pulmonary embolus 24 hours af t er a long bone f ract ure. Aort ic t hromboemboli have an impact in t he renal art eries or t hose of t he low er limb. SCC pp 44–46

Surgery 2002 20: 1; iii–vii

A 12. A. f alse

B. t rue

C. f alse

D. t rue

E. f alse

B. t rue

C. f alse

D. t rue

Answ ers

Haemodynamic inst abilit y is an indicat ion f or immediat e explorat ion. Disrupt ion is t he most common vascular injury f ollow ed by int imal injury. Shunt ing can be a very usef ul t echnique f or damage cont rol. Packing is usef ul f or venous rat her t han art erial injuries. A 13. A. t rue

Cardiovascular System

A 11. A. t rue

E. f alse

M anagement of WBC mediat ed react ions is t o slow t he t ransf usion and administ er ant ipyret ics and ant ihist amines. M assive t ransf usion is def ined as t he t ransf usion of t he ent ire blood volume in 24 hours. SCC pp 38–41

Surgery 2000 18: 2; 48–53

A 14. A. f alse

B. t rue

C. f alse

D. f alse

E. f alse

The classif icat ion of haemorrhagic shock is essent ial. Det ailed t ables can be f ound on page 30 in Surgical Crit ical Care (GM M Lt d, 2001) or Surgery 2000 18: 3; 65–68. Syst olic BP is normal in class II, pulse pressure normal or elevat ed in class I, and conf usion present in classes III and IV. Class III shock is 30–40% blood loss and is associat ed w it h a urine out put of 5–15 ml/hr. SCC pp 29–32

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65

A 15. A. f alse

B. t rue

C. t rue

D. t rue

E. t rue

The causes of arrhyt hmias are: Physiological:

Cardiovascular System

䊏 䊏 䊏 䊏

Acidosis Increased CO2 Decreased O2 Elect rolyt e imbalance

Pat hological: 䊏 䊏 䊏 䊏

Pain Phaeochromocyt oma MI Pulmonary embolus

Pharmacological: 䊏 䊏

General and local (t oxic dose) anaest het ics Inot ropes

Answ ers

SCC p 51

A 16. A. t rue

B. t rue

C. f alse

D. t rue

E. t rue

Support ive elect rocardiogram (ECG) changes include right vent ricular st rain (t he S1Q3T3 pat t ern), right axis deviat ion, right bundle branch block and at rial f ibrillat ion (AF). SCC p 22

A 17. A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

Prof use bleeding. Coagulat ion Test s: Increased PT, Increased act ivat ed part ial t hromboplast in t ime (APTT), Increased t hrombin t ime (TT), Increased f ibrin degradat ion product s (FDP), Decreased f ibrinogen. Haemat ology: Decreased plat elet s, leucocyt osis (w it h lef t shif t ). SCC pp 47–49

66

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Key Quest ions in Surgical Crit ical Care

A 18. A. t rue

B. f alse

C. f alse

D. t rue

E. f alse

Hart mann’s solut ion is isot onic and cont ains 5 mmol/l pot assium. N Saline pH ⫽ 5.0.

SCC p 140

A 19. A. f alse

B. t rue

C. f alse

D. t rue

E. t rue

VT suggest s eit her peri-operat ive myocardial damage or ongoing myocardial ischaemia. Low urine out put should be managed sequent ially by f luid load, dopamine 2 ␮G/kg/min and t hen loop diuret ic. SCC pp 49–55

Surgery 1996 14: 4; 78–81

A 20. A. t rue

B. t rue

C. f alse

D. f alse

E. t rue

SCC pp 49–55

B. t rue

C. t rue

D. f alse

Answ ers

A blood loss of 250 ml w ould make t he surgeon consider re-explorat ion, t he loss should be ⬍100 ml. New Q w aves are indicat ive of localised M I and occur in less t han 5% of pat ient s.

A 21. A. t rue

Cardiovascular System

10% of inf used 5% dext rose remains int ravascular.

E. f alse

Causes of cardiac out put can be divided int o reduced preload (hypovolaemia, cardiac t amponade, t ension pneumot horax, right vent ricular dysf unct ion and posit ive pressure vent ilat ion); reduced cont ract ilit y (myocardial ischaemia and damage, arryt hmias, hypoxia, hypercapnia and acidosis) and increased af t er load (vasoconst rict ion and f luid overload) SCC pp 51–52

Surgery 1996 14: 1; 1–5

A 22. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

The f ollow ing may be measured w it h a pulmonary art ery f lot at ion cat het er (PAFC) 䊏 䊏 䊏

M CQs

Right and lef t side cardiac f illing pressures Syst emic and pulmonary vascular resist ance M ixed venous oxygen sat urat ion

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67

䊏 䊏 䊏 䊏

Pulmonary art ery pressure Cardiac out put Core blood t emperat ure Drug delivery is also possible

Cardiovascular System

SCC pp 18–20

Surgery 2002 20: 3; 54–57

A 23. A. f alse

B. t rue

C. f alse

D. t rue

E. t rue

Causes of pulseless elect rical act ivit y (PEA) can be: Primary 䊏 䊏 䊏

MI Drugs (␤-blocker, calcium ant agonist s) Elect rolyt e imbalance (hyperkalaemia, hypocalcaemia)

Secondary 䊏 䊏 䊏

Answ ers

䊏 䊏

Tension pneumot horax Hypovolaemia Cardiac t amponade Pulmonary embolus Cardiac rupt ure SCC p 11, pp 13–14

A 24. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Dopamine st imulat es cardiac ␤-1 recept ors especially at doses of 5–10 ␮g/kg/min. The prof ound t issue damage of ext ravasat ion is mediat ed by ␣-1 induced vasoconst rict ion. SCC pp 6–7

A 25. A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

Shock should be t reat ed as volume deplet ion init ially. PAFC are of t en necessary. Vasoact ive agent s maint ain mean art erial pressure. Norepinephrine improves renal f unct ion. SCC pp 29–32

A 26. A. t rue

B. t rue

C. f alse

D. f alse

E. t rue

Cardiac out put (CO) ⫽ st roke volume (SV) ⫻ heart rat e (HR)

It can be correct ed f or body surf ace area, w hen it is called t he cardiac index (normal range 2.5–4 l/min/m 2). An increase in f illing 68

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SCC pp 3–11

A 27. A. t rue

B. f alse

C. t rue

D. t rue

E. t rue

About 80% of t ot al blood volume is cont ained w it hin t he ‘low pressure’ syst emic veins, right heart and pulmonary circulat ion. Only about 20% , t heref ore, is in t he syst emic art erial circulat ion. A low cent ral venous pressure (CVP) indicat es hypovolaemia. A raised CVP may be caused by volume overload (heart , renal or hepat ic f ailure), pulmonary hypert ension, cardiac t amponade, const rict ive pericardit is, t ricuspid valve disease, or SVC obst ruct ion.

Answ ers

The cent ral cont rol of t he circulat ion is eff ect ed by t he medullopont ine region of t he brain. It receives nervous impulses f rom st ret ch or pressure recept ors in t he aort a and carot id sinus, and in t he vena cava, at ria and lef t vent ricle. An acut e increase in blood pressure increases t he rat e of aff erent impulses and causes an increase in vagal discharge result ing in reduced myocardial cont ract ilit y, and a reduct ion in sympat het ic discharge causing vasodilat at ion and reduced peripheral resist ance. Conversely, an acut e f all in blood pressure result s in opposit e homeost at ic responses.

Cardiovascular System

pressure or preload causes an increase in vent ricular end-diast olic volume. This st ret ches myof ibrils and increases myocardial cont ract ilit y and hence cardiac out put . This relat ionship bet w een myof ibril pre-st ret ching and myocardial cont ract ilit y is called St arling’s Law.

SCC pp 3–11

A 28. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

The preload or f illing pressure of t he right heart is right at rial pressure. That of t he lef t heart is lef t at rial pressure. Assuming t here is no valve disease, at rial pressure equat es t o vent ricular end-diast olic pressure. There is a direct relat ionship bet w een f illing pressure or preload and myocardial cont ract ilit y. An increase in preload result s in an increase in vent ricular end-diast olic volume and an increase in t he amount of myof ibril st ret ch at t he onset of syst ole. This result s in an increase in myocardial cont ract ilit y.

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Cardiovascular System

This relat ionship can be used t o opt imise cardiac out put in low out put st at es w hen t he administ rat ion of f luid w it h pulmonary art ery occlusion pressure (PAOP) monit oring may increase cardiac out put . It should be not ed, how ever, t hat t he response is reduced w hen vent ricular f unct ion is impaired and t hat t he over-administ rat ion of f luid may increase pulmonary venous pressure enough t o precipit at e pulmonary oedema. SCC pp 3–11

A 29. A. t rue

B. f alse

C. t rue

D. t rue

E. t rue

Af t erload is det ermined by t he aort ic valve, peripheral vascular resist ance and compliance of t he major vessels. There is a direct relat ionship bet w een af t erload and peripheral vascular resist ance. At any given preload, decreasing t he af t erload increases st roke volume. Cardiac work/beat ⫽ stroke work ⫽ stroke volume ⫻ mean aortic pressure.

Answ ers

A reduct ion in af t erload generally decreases myocardial oxygen demand. SCC pp 3–11

A 30. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

The blood oxygen cont ent or amount of oxygen bound by haemoglobin is det ermined by t he haemoglobin concent rat ion and sat urat ion. Cardiac out put , haemat ocrit and local vasomot or t one det ermine t issue blood f low. Pyrexia, decreasing pH, and increasing concent rat ions of 2,3-diphosphoglycerat e (2,3-DPG) generat ed by glycolysis shif t t he oxyhaemoglobin dissociat ion curve t o t he right , reducing haemoglobin aff init y f or oxygen and f avour oxygen release t o t he t issues. SCC pp 76–78

A 31. A. f alse

B. t rue

C. f alse

D. f alse

E. t rue

Epinephrine and dobut amine are posit ive inot ropes act ing at cardiac ␤-recept ors. M yocardial cont ract ilit y is reduced by hypoxia, acidosis and sepsis. Nit rat es are neut ral but may improve myocardial cont ract ilit y indirect ly in pat ient s w it h coronary art ery disease t hrough coronary vasodilat at ion and increased myocardial perf usion. Nit rat es also cause peripheral 70

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vasodilat at ion, causing a reduct ion in preload and pulmonary venous pressure, w hich is benef icial in heart f ailure. SCC pp 3–4, pp 6–8

B. t rue

C. f alse

D. f alse

E. f alse

Act ivat ion of t he sympat het ic nervous syst em increases heart rat e w hich (in t he early st ages of heart f ailure) compensat es f or t he reduced st roke volume (CO ⫽ SV ⫻ HR). Reduced renal perf usion result s in act ivat ion of t he renin-angiot ensin-aldost erone (RAA) syst em, w hich causes sodium and w at er ret ent ion and cont ribut es t o t he increase in venous pressure seen in heart f ailure. The increase in venous pressure (preload) and associat ed vent ricular end-diast olic volume increases myof ibril st ret ching and result s in an increase in myocardial cont ract ilit y (St arling’s Law ). Act ivat ion of t he sympat het ic nervous syst em and t he RAA syst em bot h cause vasoconst rict ion.

A 33. A. t rue

B. t rue

C. t rue

D. f alse

E. f alse

Answ ers

SCC pp 4–5

Cardiovascular System

A 32. A. f alse

As st roke volume decreases, vent ricular end-diast olic volume and hence muscle f ibre pre-st ret ching is increased. Through St arling’s Law, myocardial cont ract ilit y is increased. The increase in lef t vent ricular diast olic pressure causes an increase in lef t at rial pressure ref lect ed in an increase in pulmonary art ery occlusion pressure (PAOP). Increased sympat het ic act ivat ion causes vasoconst rict ion and an increase in syst emic vascular resist ance (SVR). SCC pp 3–5

A 34. A. f alse

B. t rue

C. f alse

D. f alse

E. t rue

The CVP, ref lect ed clinically by t he jugular venous pressure (JVP), is most commonly raised due t o volume overload (heart f ailure, renal f ailure, hepat ic f ailure). Ot her causes include pulmonary hypert ension (e.g. pulmonary embolism (PE), hypoxic lung disease), t ricuspid regurgit at ion, and SVC obst ruct ion w hen t he JVP has a f ixed w ave f orm. In cardiac t amponade and const rict ive pericardit is, Kussmaul’s sign may be present , w hen t he JVP rises

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on inspirat ion compared w it h t he normal f all on inspirat ion. Sepsis is charact erised by a vasodilat ed st at e so t here is usually relat ive hypovolaemia. SCC pp 16–18

Cardiovascular System

A 35. A. f alse

B. t rue

C. t rue

D. t rue

E. t rue

The subclavian vein t raverses ant erior t o t he apex of t he lung. Risk of pneumot horax is t heref ore great er w it h t his approach compared w it h t he int ernal jugular approach. Nevert heless, a pneumot horax should be excluded by a chest X-ray af t er eit her approach.

Answ ers

The risk of accident al art erial punct ure exist s w it h bot h subclavian and int ernal jugular approaches. The subclavian art ery, how ever, cannot be compressed eff ect ively af t er accident al punct ure. In pat ient s w it h clot t ing abnormalit ies or t hrombocyt openia, t hese should be correct ed prior t o cent ral line insert ion. If vascular access rat her t han CVP monit oring is required in t hese pat ient s, cannulat ion of t he f emoral vein is saf er as haemost asis af t er accident al punct ure of t he f emoral art ery is usually rapidly obt ained. CVP monit oring measures right heart preload/f illing pressure. This may not ref lect t he f illing pressure of t he lef t heart w hen t here is disparit y bet w een lef t and right heart f unct ion e.g. lef t heart f ailure, pulmonary hypert ension (PE, hypoxic lung disease). SCC pp 16–18

A 36. A. t rue

B. f alse

C. f alse

D. t rue

E. t rue

PAOP is measured by t emporary occlusion of a pulmonary art ery branch by a balloon f lot at ion cat het er. It does not require radiological screening as t he balloon-t ipped cat het er is f low -direct ed t hrough t he right heart t o t he pulmonary art ery and so can be perf ormed in t he high dependency unit (HDU) set t ing. The posit ion of t he cat het er is ident if ied f rom t he pressure w avef orm t ransduced f rom t he cat het er t ip. Occlusion of a pulmonary art ery by t he inf lat ed balloon means t hat only t he low -pressure pulmonary veins lie bet w een t he cat het er t ip and t he lef t at rium. The balloon should be inf lat ed prior t o t he advancement of t he cat het er int o t he pulmonary art ery w hen measuring t he PAOP. 72

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SCC pp 17–19

A 37. A. f alse

B. f alse

C. t rue

D. f alse

E. f alse

PAOP is a ref lect ion of lef t at rial pressure, t he f illing pressure of t he lef t heart . It is t he most usef ul object ive measure of volume st at us in pat ient s in w hom t his remains uncert ain af t er clinical assessment and CVP measurement .

SCC pp 17–19

A 38. A. f alse

B. t rue

C. t rue

D. t rue

Answ ers

Adult respirat ory dist ress syndrome (ARDS) is charact erised by pulmonary oedema in t he presence of a low or normal PAOP. Sept ic shock is charact erised by vasodilat at ion and PAOP is usually low.

Cardiovascular System

Inf lat ion of t he balloon w it hin a pulmonary art ery branch can cause rupt ure of t he vessel w it h haemopt ysis and occasionally deat h. The balloon should be def lat ed af t er measurement of PAOP ot herw ise pulmonary inf arct ion can result . Ot her complicat ions include knot t ing of t he cat het er, sepsis, and balloon rupt ure. Arrhyt hmias are common but almost invariably t ransient during advancement of t he cat het er t hrough t he right heart .

E. f alse

The t w o most usef ul met hods of quant if ying cardiac out put in t he HDU set t ing are by t hermodilut ion and oesophageal Doppler. In t hermodilut ion, 10 ml cold cryst alloid is inject ed int o t he right at rial port of a pulmonary art ery cat het er. A t hermist or at t he cat het er t ip measures t he result ant t ransient t emperat ure decrease in t he pulmonary art ery. The area under t he f all in t emperat ure against t ime curve correlat es w it h cardiac out put , w hich is calculat ed by comput er. The oesophageal Doppler probe measures the velocity of blood flow within the descending thoracic aorta. The area within the velocity-time waveform multiplied by the aortic cross-sectional area (obtained from a nomogram based upon age, height and weight) is aortic blood flow, from which cardiac output can be derived. Using t he Fick principle, CO =

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oxygen consumption arteriovenousoxygen content difference

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Cardiovascular System

The main diff icult y is an accurat e measurement of oxygen consumpt ion, so oxygen consumpt ion is of t en assumed on t he basis of age, gender and body surf ace area (Indirect Fick met hod). The addit ional variables required t o calculat e art erial and mixed venous oxygen cont ent are haemoglobin concent rat ion, and oxygen sat urat ion in art erial blood and mixed venous (pulmonary art ery) blood. SCC pp 18–20

A 39. A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

Normal PAOP: 4–12 mmHg. Raised values indicat e volume overload or mit ral valve disease. Normal SVR: 700–1600 dyn s/cm 5. Low values indicat e a vasodilat ed st at e such as in sept ic shock or t he syst emic inf lammat ory response syndrome. Raised values occur in hypovolaemia, heart f ailure and cardiogenic shock. SCC pp 18–20

Answ ers

A 40. A. t rue

B. t rue

C. f alse

D. f alse

E. t rue

Cardiogenic shock is charact erised by a low cardiac out put , and raised PAOP and SVR. The raised PAOP ref lect s t he elevat ed lef t vent ricular end-diast olic and lef t at rial pressures t hat accompany lef t vent ricular dysf unct ion. The raised SVR ref lect s sympat het ic act ivat ion, w hich causes vasoconst rict ion. The most common cause of cardiogenic shock is acut e M I. Ot her causes include arrhyt hmias, myocardit is, valve disease including endocardit is, aort ic dissect ion and myocardial depression due t o drugs, sepsis and hypoxia. M anagement involves monit oring of cardiac rhyt hm, and invasive blood pressure and CVP monit oring. M easurement of PAOP may be indicat ed if volume st at us remains uncert ain. Oxygen, int ravenous diuret ics, and inot ropes are invariably required. Int ra-aort ic balloon pumping (IABP) may be indicat ed, part icularly w hen t here is a pot ent ially correct able cause such as acut e mit ral regurgit at ion due t o papillary muscle rupt ure, or vent ricular sept al def ect (VSD) complicat ing M I. SCC pp 29–32

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A 41. A. t rue

B. f alse

C. f alse

D. f alse

E. f alse

SCC pp 29–32

A 42. A. f alse

B. f alse

C. t rue

D. t rue

Cardiovascular System

Septic shock is most commonly caused by gram-negative sepsis (E. coli, Meningoccocus) or Staphylococcus aureus. Endotoxins cause vasodilatation and increased capillary permeability resulting in hypotension and leakage of fluid from the capillary bed. Cardiac output is usually increased but may be low once metabolic acidosis has supervened. Vasodilatation results in a low SVR. Management includes treatment of the underlying cause (e.g. surgery for intra-abdominal sepsis, antibiotics), correction of hypovolaemia and vasoconstrictive inotropes such as noradrenaline.

E. t rue

Answ ers

The P w ave represent s at rial depolarisat ion t hat t riggers at rial cont ract ion and t heref ore occurs in diast ole. There is an inherent delay in conduct ion as it passes t hrough t he at riovent ricular node, ref lect ed by t he PR int erval, w hich allow s t he vent ricle t o f ill prior t o vent ricular cont ract ion. Vent ricular depolarisat ion is ref lect ed by t he QRS complex and vent ricular repolarisat ion by t he T w ave. Prolongat ion of t he PR int erval ⬎200 ms is called 1st degree heart block and ref lect s delayed conduct ion t hrough t he at riovent ricular node. It may ref lect a high vagal t one in young, f it adult s, or can be caused by M I, ␤-blockers, calcium channel blockers, hypot hyroidism, hypot hermia, or age-relat ed degenerat ion of t he conduct ing syst em. In isolat ion, it requires no t reat ment . SCC pp 20–22

A 43. A. t rue

B. t rue

C. t rue

D. f alse

E. t rue

It should be remembered t hat myocardial ischaemia is not t he only cause of ST depression. Lef t vent ricular hypert rophy can cause ST depression and T w ave inversion in t he inf erolat eral leads, w hen it is commonly ref erred t o as a ‘st rain pat t ern’. Digoxin may give rise t o ‘reversed t ick’ ST depression in t he absence of t oxicit y. Lef t bundle branch block result s in abnormal vent ricular depolarisat ion (broad QRS complex) and

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repolarisat ion (giving rise t o ST depression and T w ave inversion in t he lat eral leads). SCC pp 20–23

Cardiovascular System

A 44. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

The charact erist ic ECG change of M I is ST elevat ion, t hough t his may also be caused by pericardit is and lef t vent ricular aneurysm. The ECG may, how ever, be normal or reveal only minor ST/T w ave changes. Lef t bundle branch block may be caused by ant erior M I. Complet e heart block is relat ively common in inf erior M I, w hen it can usually be managed expect ant ly. Insert ion of a t emporary pacing w ire is indicat ed w hen complet e heart block occurs in associat ion w it h ant erior M I. SCC pp 22–23

A 45. A. f alse

B. t rue

C. f alse

D. t rue

E. f alse

Answ ers

The diagnosis of post -operat ive M I may be diff icult , part icularly af t er cardiac surgery because creat ine kinase is released f rom t raumat ised skelet al muscle, and handling of t he heart may cause minor ECG changes. Creat inine kinase M B is more specif ic, but t roponin T or I are t he most specif ic markers of myocardial injury. Cardiac monit oring is mandat ory in t he f irst 36 hours af t er M I as pot ent ially f at al but t reat able vent ricular t achyarrhyt hmias occur most commonly early af t er M I. Thrombolyt ic t herapy is cont ra-indicat ed w it hin 6 w eeks of major surgery, but aspirin improves prognosis t o a similar ext ent and should be administ ered in suspect ed M I. Nit rat es do not inf luence prognosis but are usef ul f or t he t reat ment of cont inuing chest pain or associat ed lef t vent ricular f ailure. SCC pp 49–55

A 46. A. f alse

B. t rue

C. t rue

D. f alse

E. t rue

Bot h a VSD and mit ral regurgit at ion due t o papillary muscle rupt ure cause a new pansyst olic murmur af t er M I, of t en associat ed w it h cardiogenic shock and so may be conf used clinically. Lef t vent ricular pressure is higher t han right vent ricular 76

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SCC pp 49–55

A 47. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Answ ers

A small PE may result in no abnormal physical signs or changes on t he ECG, so clinical suspicion must be high, part icularly in t hose at risk e.g. post -operat ive pat ient s, t he immobile, t hose w it h heart f ailure or malignancy. Obst ruct ion of a major pulmonary art ery branch causes an increase in right -sided heart pressures w it h elevat ion of t he JVP and dilat at ion of t he right vent ricle on echo. Hypoxia and hypervent ilat ion producing a low pCO2 (t ype I respirat ory f ailure) are t ypical of a large PE.

Cardiovascular System

pressure so blood passes t hrough t he VSD f rom t he lef t t o right vent ricle and pulmonary blood f low is increased. The diagnosis can normally be made by t ranst horacic echocardiography. If cardiac cat het erisat ion is perf ormed, a ‘st ep-up’ in oxygen sat urat ion is demonst rat ed in t he right vent ricle and pulmonary art ery compared w it h t he right at rium as t he blood passing f rom lef t t o right vent ricle is oxygenat ed. M anagement may be conservat ive f or a small VSD w it hout haemodynamic compromise, or involve support ive measures including IABP and inot ropes prior t o surgical closure.

SCC pp 45–46

A 48. A. t rue

B. f alse

C. t rue

D. t rue

E. f alse

Risk of PE is increased by pelvic and low er limb surgery t hrough t rauma t o t he iliac and f emoral veins, a subst rat e f or deep vein t hrombosis. The risk of t hromboembolism associat ed w it h malignancy is mult if act orial and includes venous compression by t umour, release of prot hrombot ic mediat ors, dehydrat ion and immobilit y. Ot her risk f act ors f or t hromboembolism include heart f ailure, polycyt haemia and prot hrombot ic condit ions e.g. f act or V Leiden and f act or C & S def iciency. SCC pp 45–46

A 49. A. t rue

B. t rue

C. f alse

D. t rue

E. t rue

Post -operat ive pulmonary oedema is commonly caused by pre-exist ing lef t vent ricular dysf unct ion, peri-operat ive myocardial ischaemia or inf arct ion, or overly aggressive

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int ravenous f luid administ rat ion, but may be non-cardiogenic in origin (ARDS), part icularly in t he set t ing of sepsis or af t er cardiopulmonary bypass (CPB).

Cardiovascular System

In pat ient s w ho chronically ret ain CO2 (most commonly in chronic obst ruct ive pulmonary disease (COPD)), t reat ment w it h high-f low oxygen may remove t heir hypoxic drive t o vent ilat ion result ing in hypovent ilat ion and progressive t ype II respirat ory f ailure. Nevert heless, it is t he hypoxia associat ed w it h pulmonary oedema t hat is acut ely lif e-t hreat ening and t his must be rapidly correct ed. The development of hypercapnia may require noninvasive or invasive vent ilat ory support . Int ravenous opiat e act s as a venodilat or reducing pulmonary venous pressure, and as an anxiolyt ic. SCC pp 4–5, pp 32–36

A 50. A. f alse

B. f alse

C. t rue

D. t rue

E. f alse

Answ ers

The pat ient should be nursed sit t ing up. High f low oxygen, int ravenous opiat e, diuret ic and nit rat e should be administ ered. Opiat es act as venodilat ors and anxiolyt ics. Int ravenous f rusemide is also a venodilat or in addit ion t o it s diuret ic propert ies. Nit rat es are venodilat ors, reducing preload and pulmonary venous pressure. ␤-blockers and angiot ensin convert ing enzyme (ACE) inhibit ors improve prognosis in chronic heart f ailure, but t heir int roduct ion should be delayed unt il acut e pulmonary oedema has been t reat ed. SCC pp 32–36

A 51. A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

Hypovolaemia is probably t he commonest cause of hypot ension af t er surgery so volume st at us must be assessed, including review of f luid balance chart s. Hypovolaemia is of t en mult if act orial w it h ‘nil by mout h’, f luid losses f rom vomit ing, drains, f ist ulae and int ra-abdominal sequest rat ion cont ribut ing. Post -operat ive pat ient s are at risk of PE, w hich may cause hypot ension t hrough obst ruct ion of blood f low t hrough a major pulmonary art ery. Sepsis causes hypot ension t hrough vasodilat at ion. Treat ment is t hrough t reat ing t he cause e.g. laparot omy f or int ra-abdominal sepsis, volume replacement , ant ibiot ics, and inot ropes. SCC pp 49–55

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A 52. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

A 53. A. t rue

B. t rue

C. f alse

D. f alse

Answ ers

SCC pp 49–55

Cardiovascular System

The cause of hypot ension af t er cardiac surgery may be obvious, e.g. f rom haemorrhage apparent f rom drain blood loss, w hich requires surgical explorat ion. Cardiac t amponade should be suspect ed w hen hypot ension occurs in t he presence of raised venous pressure. Transt horacic echo (TTE) is t he init ial invest igat ion, but t ransoesophageal echo (TOE) may be required t o ident if y compressive t hrombus localised around t he right at rium. Lef t vent ricular dysf unct ion may be present preoperat ively and is compounded by peri-operat ive myocardial ischaemia, arrhyt hmias, hypoxia and acidosis. Heart block and bundle branch block are common, part icularly af t er valvular surgery, due t o damage t o t he conduct ing syst em. Ext ernal pacing w ires are placed at surgery and allow expect ant management aw ait ing spont aneous ret urn of normal conduct ion, but permanent pacemaker insert ion is indicat ed if advanced heart block persist s af t er 7–10 days. CPB is associat ed w it h a syst emic inf lammat ory response due t o act ivat ion of inf lammat ory mediat ors as blood passes t hrough t he ‘f oreign’ ext ra-corporeal circuit . This is usually a self -limit ing process but can progress t o syst emic inf lammat ory response syndrome (SIRS).

E. f alse

AF occurs in 20–40% pat ient s af t er coronary bypass graf t ing and is st ill more common af t er valve replacement . AF is charact erised by t he absence of P w ave act ivit y and t he QRS complexes are irregular (except w hen complet e heart block coexist s). The arrhyt hmia is usually self -limit ing af t er cardiac surgery, assuming pre-operat ive sinus rhyt hm. Nevert heless, it s occurrence prolongs hospit al st ay and increases use of resources as spont aneous cardioversion, vent ricular rat e cont rol and/or w arf arinisat ion is achieved. SCC pp 49–55

A 54. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Post -operat ive AF is of t en self -limit ing. How ever, it s occurrence may cause t roublesome palpit at ion or promot e myocardial

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Cardiovascular System

ischaemia or heart f ailure. Persist ent AF is associat ed w it h an increased incidence of t hromboembolic st roke. The appropriat e management st rat egy is dependent upon w het her haemodynamic compromise is present and on t he vent ricular rat e. If signif icant haemodynamic compromise is t hought t o be caused by t he new occurrence of AF, t hen DC cardioversion should be perf ormed. The asympt omat ic pat ient can be managed expect ant ly, w it h vent ricular rat e cont rol unt il t he ret urn of sinus rhyt hm. Digoxin, ␤-blockers and verapamil can be used f or rat e cont rol. If t he AF persist s, cardioversion should be considered. This can be perf ormed w it hout ant icoagulat ion if t he onset of AF occurred w it hin 48 hours as t he risk of lef t at rial t hrombus f ormat ion is low w it hin t his t ime-f rame. Thereaf t er, 4 w eeks of w arf arin prior t o cardioversion (as an out pat ient ) is recommended. Cardioversion can be achieved elect rically or pharmacologically using agent s such as amiodarone. All pat ient s w it h persist ent AF, except t hose aged ⬍65 years w it h lone AF, should be considered f or w arf arin t o prevent st roke.

Answ ers

SCC pp 4–5, pp 49–51

A 55. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Conduct ion disorders including complet e heart block occur due t o damage t o t he conduct ing syst em at surgery. The conduct ion disorder may be permanent or resolve spont aneously. Second or t hird degree heart block persist ing af t er 7–10 days requires insert ion of a permanent pacemaker. Endocardit is occurring in t he early post -operat ive period is most commonly caused by coagulase-negat ive St aphylococci and St aphylococcus aureus. CPB is associat ed w it h a syst emic inf lammat ory response due t o act ivat ion of inf lammat ory mediat ors as blood passes t hrough t he ext ra-corporeal circuit . It is usually self -limit ing but may cause mult i-syst em f ailure. When cardiac t amponade occurs as an early complicat ion of cardiac surgery, it usually requires surgical drainage. Neurocognit ive impairment is of mult if act orial aet iology w it h f act ors including CPB, aort ic cross-clamping, and t hromboembolic event s cont ribut ing. SCC pp 49–55

80

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A 56. A. f alse

B. t rue

C. t rue

D. f alse

E. f alse

A 57. A. f alse

B. f alse

C. f alse

D. t rue

Answ ers

SCC pp 49–55

Cardiovascular System

Hypot ension and a raised jugular venous or cent ral venous pressure should raise t he suspicion of cardiac t amponade. Cardiac t amponade may result in an increase in t he venous pressure on inspirat ion (Kussmaul’s sign) rat her t han t he usual decrease. Pulsus paradoxus (a decrease in syst olic blood pressure ⬎10 mmHg during normal inspirat ion) may be present . Bot h physical signs ref lect t he increased int ra-pericardial pressure t hat compresses t he heart . The increased venous ret urn t hat usually occurs on inspirat ion is const rained causing an increase in right -sided pressures. The at rial and vent ricular sept ae are pushed t o t he lef t reducing lef t vent ricular st roke volume and blood pressure. The diagnosis is usually made by t ranst horacic echo. TOE may be required t o demonst rat e localised eff usion or clot t hat can occur due t o pericardial adhesions af t er surgery. M anagement of t amponade early af t er surgery is usually surgical drainage because t he presence of adhesions and t hrombus make needle aspirat ion impract ical. Corrigan’s sign is a sign of aort ic regurgit at ion and pulsus alt ernans is a sign of severe impairment of lef t vent ricular f unct ion.

E. t rue

Pericardiocent esis is indicat ed in t he absence of t amponade w hen t he diagnosis of pericardial eff usion is uncert ain. Pericardial f luid should be sent f or prot ein concent rat ion, microscopy and cult ure including TB, cyt ology, and rheumat oid f act or. M alignant disease is a common cause of pericardial eff usion and pericardiocent esis may be indicat ed f or diagnosis, t reat ment of sympt oms (t ypically breat hlessness) in t he absence of f rank t amponade, or t amponade. Such eff usions f requent ly reaccumulat e, how ever, w hen a pericardial w indow should be considered. Pericardiocent esis is usually perf ormed by t he subxiphoid approach w it h t he pat ient reclining at 45 degrees. The aspirat ion needle is advanced t ow ards t he lef t scapula. Echo and X-ray screening can bot h be used t o guide needle placement w it hin t he pericardial space. Complicat ions include lacerat ion of a coronary art ery or vein or cardiac chamber, vasovagal react ions, arrhyt hmias, and penet rat ion of t he st omach, colon or lung. SCC p 14, pp 227–228

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A 58. A. t rue

B. t rue

C. t rue

D. f alse

E. f alse

Cardiovascular System

Nat ive valve endocardit is at t he aort ic sit e and prost het ic valve endocardit is are most commonly associat ed w it h abscess f ormat ion. Abscess f ormat ion should be suspect ed if pyrexia and raised inf lammat ory markers persist af t er appropriat e ant ibiot ic t herapy. New -onset conduct ion disorders are not sensit ive but are relat ively specif ic (about 85% ) markers f or abscess f ormat ion. Aort ic root abscess is an indicat ion f or aort ic valve replacement and abscess ablat ion. Abscesses are usually def ined by t ransoesophageal rat her t han t ranst horacic echo. SCC p 27

A 59. A. t rue

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D. t rue

E. f alse

Answ ers

The indicat ions f or surgery in endocardit is are haemodynamic compromise due t o valve dysf unct ion, f ailure of appropriat e ant ibiot ic t herapy t o eradicat e inf ect ion as indicat ed by persist ent f ever and raised inf lammat ory markers, aort ic root abscess, an unst able prost hesis, and recurrent emboli f rom an inf ect ed valve. Alt hough prost het ic valve endocardit is is not an absolut e indicat ion f or redo valve replacement , it is uncommon f or inf ect ion t o be eradicat ed f rom a prost het ic valve by ant ibiot ic t herapy alone. If inf ect ion is successf ully eradicat ed by ant ibiot ic t herapy w it h lit t le result ant valve dysf unct ion, a conservat ive approach t o management can be pursued. A 60. A. f alse

B. t rue

C. t rue

D. t rue

E. f alse

Aort ic dissect ion is t hought t o begin w it h a t ear in t he aort ic int ima, w hich exposes a diseased media t o blood at syst emic art erial pressure. The classical hist ological change seen in M arf an’s syndrome is cyst ic medial necrosis. Ot her condit ions t hat predispose t o aort ic dissect ion are hypert ension, bicuspid aort ic valve, coarct at ion, Ehlers-Danlos syndrome, Noonan and Turner syndromes, pregnancy and t rauma, eit her ext ernal chest t rauma or int ernal t rauma f rom a cardiac cat het er or balloon pump. There are a number of classif icat ions. The most import ant f eat ure is w het her t he ascending aort a is involved. The commonly used St anf ord classif icat ion has a t ype A dissect ion involving t he ascending aort a, w hile a t ype B dissect ion does not involve t he ascending aort a. 82

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A 61. A. f alse

B. t rue

C. t rue

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E. t rue

In t ype A (proximal) dissect ions, aort ic regurgit at ion may result eit her f rom det achment of an aort ic leaf let or dilat at ion of t he aort ic root . In 1–2% cases, a proximal dissect ion f lap involves t he ost ium of a coronary art ery (more commonly t he right ) causing M I. Ext ension of t he dissect ion int o t he abdominal aort a may compromise one or bot h renal art eries or t he iliac art eries.

A 62. A. f alse

B. t rue

C. f alse

D. f alse

E. f alse

Answ ers

Pleural eff usions are common, usually lef t -sided, and may arise eit her secondary t o an inf lammat ory react ion around t he involved aort a or by a t ransient leak f rom a descending dissect ion. Pericardial eff usion may also result f rom an inf lammat ory react ion or f rom haemorrhage int o t he pericardial space f rom t he dissect ed aort ic root .

Cardiovascular System

Aort ic dissect ion usually present s w it h pain, classically t earing in charact er. Ot her sympt oms and signs depend upon t he locat ion of t he dissect ion and involvement of major art erial branches. Signs may include reduced or absent pulses, aort ic regurgit at ion, hemi- or paraplegia.

The diagnost ic invest igat ions f or aort ic dissect ion are M RI, cont rast -enhanced CT scanning, TOE and aort ography. M RI has a near 100% sensit ivit y and specif icit y f or t he det ect ion of aort ic dissect ion, and does not require t he use of ionising radiat ion or cont rast . How ever, availabilit y of scanners remains limit ed, and monit oring of and access t o unst able pat ient s is compromised in t he M RI suit e. CT scanning is available at most inst it ut ions and is complet ed more rapidly t han M RI. Sensit ivit y and specif icit y are about 90% , w it h higher values f or spiral CT scanning. TTE has a low diagnost ic sensit ivit y and specif icit y, but is readily available, perf ormed at t he bedside and provides import ant inf ormat ion about aort ic root size, presence of aort ic regurgit at ion and pericardial eff usion, and lef t vent ricular f unct ion. TOE has a sensit ivit y and specif icit y of about 95% f or t he diagnosis of aort ic dissect ion. In unst able pat ient s, it should be perf ormed in t he anaest het ised pat ient in t he operat ing room. The int roduct ion of non-invasive diagnost ic modalit ies has seen aort ography used less f requent ly. The procedure is invasive, requires t he use of pot ent ially nephrot oxic cont rast , carries risks of t hromboembolic

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event s, vascular complicat ions, and of ent ering t he f alse lumen w it h cat het ers.

Cardiovascular System

A 63. A. f alse

B. t rue

C. t rue

D. t rue

E. t rue

TTE is readily available, non-invasive and provides real-t ime imaging making it ideal f or t he assessment of t he crit ically-ill pat ient . Image qualit y, how ever, is of t en limit ed in obese pat ient s, t hose w it h COPD, and in vent ilat ed pat ient s. TOE can be perf ormed saf ely in t he int ubat ed pat ient and generally provides superior image resolut ion. Indicat ions include t he diagnosis of aort ic dissect ion or aort ic injury, source of embolus, and at rial sept al def ect . Int ra-operat ive indicat ions include t he assessment of mit ral valve repair and lef t vent ricular f unct ion. TOE has great er sensit ivit y f or t he diagnosis of endocardit is t han TTE, part icularly in prost het ic valve endocardit is, and provides addit ional inf ormat ion regarding complicat ions such as aort ic root abscess and f ist ula f ormat ion.

Answ ers

SCC pp 22–28

A 64. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Dobut amine is a synt het ic inot rope t hat st imulat es ␤-1, ␤-2 and ␣-1 recept ors. It s posit ive inot ropic act ion is t hrough st imulat ion of cardiac ␤-1 recept ors. St imulat ion of ␤-2 recept ors in peripheral vessels causes vasodilat at ion reducing peripheral vascular resist ance, at least at low doses, and t his cont ribut es t o t he increase in cardiac out put . These f avourable eff ect s on peripheral vascular resist ance make dobut amine t he f avoured inot rope in cardiogenic shock, part icularly in t he set t ing of ischaemic heart disease. By cont rast , dopamine t ends t o increase peripheral vascular resist ance and causes a great er increase in myocardial oxygen demand and heart rat e f or a given inot ropic eff ect . SCC pp 6–8

A 65. A. t rue

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C. f alse

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E. t rue

Epinephrine is an endogenous cat echolamine t hat st imulat es ␣- and ␤-adrenocept ors. It t ends t o produce vasoconst rict ion and an increase in af t erload, part icularly at higher doses. M yocardial 84

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SCC pp 7–8

A 66. A. f alse

B. t rue

C. t rue

D. t rue

E. f alse

Answ ers

Norepinephrine (noradrenaline) has some ␤-agonist propert ies, but act s predominant ly at ␣-adrenocept ors and is t heref ore a pot ent vasoconst rict or. It is indicat ed f or hypot ension associat ed w it h low peripheral vascular resist ance t hat persist s af t er correct ion of hypovolaemia, e.g. sept ic shock. Dopamine has a dose-dependent act ion. At low dose (⬍2 ␮g/kg/min), it causes vasodilat at ion of renal and splanchnic art eries t hrough st imulat ion of dopamine recept ors, w hich may increase urine volume. Despit e t his, dopamine has not been show n t o improve renal f unct ion or t o improve out come in renal f ailure. At int ermediat e doses (2–10 ␮g/kg/min), cardiac out put is increased t hrough ␤-adrenocept or act ivat ion. At higher doses, ␣-adrenocept ors are act ivat ed producing vasoconst rict ion. Tachycardia t ends t o be more pronounced t han w it h dobut amine.

Cardiovascular System

oxygen demand t heref ore t ends t o be great er t han w it h dobut amine f or a given increase in cardiac out put , and myocardial ischaemia may be precipit at ed, part icularly in pat ient s w it h know n coronary art ery disease. Current advanced lif e support (ALS) guidelines recommend t he administ rat ion of epinephrine 1 mg every 3 minut es of cardiopulmonary resuscit at ion. At t his dose, it produces vasoconst rict ion and increases peripheral vascular resist ance, result ing in a relat ive increase in cerebral and coronary perf usion. If vascular access is not available, epinephrine can be given dow n t he endot racheal t ube, w hen t he dose should be doubled.

SCC pp 7–8

A 67. A. f alse

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C. t rue

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E. t rue

The IABP is posit ioned via a f emoral art ery in t he descending t horacic aort a w it h t he balloon t ip dist al t o t he lef t subclavian art ery. The IABP can be insert ed on t he w ard w hen t he posit ion is checked by chest X-ray, or under radiological screening. The balloon is t imed t o inf lat e during diast ole and def lat e just prior t o t he onset of syst ole. Diast olic pressure is augment ed and af t erload is reduced result ing in increased coronary and cerebral

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Cardiovascular System

perf usion and a reduct ion in myocardial oxygen demand. The balloon can be inf lat ed every cardiac cycle or 1:2 or 1:3 cardiac cycles, w hich allow s w eaning f rom t he balloon w hen t he pat ient has st abilised. The ‘f oreign’ balloon w it hin t he circulat ion is a st imulus t o t hrombus f ormat ion so f ull heparinisat ion is required. SCC p 8

A 68. A. t rue

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C. f alse

D. t rue

E. f alse

Answ ers

The IABP result s in a reduct ion in af t erload and myocardial oxygen demand, and an increase in coronary and cerebral perf usion. In t he clinical set t ing, it is most commonly used as a st abilising measure prior t o def init ive surgical int ervent ion. Indicat ions f or IABP include ref ract ory angina (t ypically in pat ient s w it h lef t main st em disease, severe t hree vessel disease, or crit ical vein graf t disease prior t o coronary bypass surgery), and cardiogenic shock caused by mit ral regurgit at ion or VSD post -myocardial inf arct ion. IABP is cont ra-indicat ed in pat ient s w it h signif icant aort ic regurgit at ion (w hich it exacerbat es), aort ic dissect ion, aort ic aneurysm, and severe peripheral vascular disease. IABP may be complicat ed by low er limb ischaemia, t hromboembolism, balloon rupt ure or ent rapment , sepsis, and haemorrhage relat ed t o t he ant icoagulat ion t hat is required. Low er limb ischaemia w arrant s balloon removal. SCC p 8

A 69. A. t rue

B. t rue

C. f alse

D. t rue

E. t rue

The f irst considerat ion in suspect ed cardiac arrest is alw ays saf et y of rescuer and vict im f rom dangers such as t raff ic, elect ricit y, gas, w at er, et c. Next check t he vict im’s responsiveness. If he responds, leave him in t he posit ion he w as f ound and get help. If he is unresponsive, call f or help, t urn him ont o his back, and open t he airw ay by ‘head t ilt /chin lif t ’. Breat hing is assessed f or no more t han 10 seconds. If he is breat hing normally, t he vict im is placed in t he recovery posit ion. If he is not breat hing, give t w o slow, eff ect ive rescue breat hs. Next check f or signs of a circulat ion (normal breat hing, movement , presence of a pulse) f or no more t han 10 seconds. If a circulat ion is present , cont inue rescue breat hing. If t here are no signs of a circulat ion, init iat e chest 86

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compressions at a rat e of 100 per minut e, w it h t w o rescue breat hs f or every 15 compressions. SCC pp 11–15

B. f alse

C. f alse

D. f alse

E. t rue

SCC pp 11–15

A 71. A. f alse

B. t rue

C. t rue

D. f alse

Answ ers

Basic lif e support (BLS) implies t hat no equipment is used during t he resuscit at ion. Rescue breat hs should t ake about 2 seconds and should be suff icient t o make t he chest rise clearly. The chest should be allow ed t o f all bef ore giving anot her rescue breat h. Chest compressions should be perf ormed at a rat e of 100 per minut e in a rat io of 15 compressions t o 2 rescue breat hs. Compressions are perf ormed on t he low er half of t he st ernum and should depress t he st ernum 4–5 cm. In BLS, compressions cease during t he rescue breat hs. By cont rast , in t he int ubat ed pat ient (ALS) compressions cont inue unint errupt ed f or vent ilat ions. Opt imally perf ormed chest compressions achieve ⬍30% of t he normal cardiac out put . Forw ard blood f low is achieved by direct compression of t he heart , and by changes in int rat horacic pressure w it h t he heart valves prevent ing backw ard f low (t he more import ant mechanism).

Cardiovascular System

A 70. A. t rue

E. f alse

Irreversible brain damage occurs w it hin 3 minut es of circulat ory arrest . BLS aims t o slow t he rat e of det eriorat ion of t he brain and heart unt il def ibrillat ion (if appropriat e) and ALS is init iat ed. BLS it self w ill rarely, if ever, rest ore an eff ect ive cardiac rhyt hm. A praecordial t hump is indicat ed only in a w it nessed cardiac arrest w hen a def ibrillat or is not immediat ely t o hand, w hen it may revert vent ricular t achycardia/vent ricular f ibrillat ion (VT/VF) back t o a perf using rhyt hm. In adult s, t he most common cardiac arrest rhyt hm is VF. The chances of successf ul def ibrillat ion decrease by 7–10% per minut e. Thus, t he cardiac rhyt hm should be est ablished at t he earliest opport unit y and a shock delivered if pulseless VT/VF is present . Def ibrillat ion should not be delayed t o perf orm cardiopulmonary resuscit at ion unless a def ibrillat or is not immediat ely available. Three shocks are given in succession if t here has been no change in rhyt hm, w it h energy levels of 200 J, 200 J and 360 J. If pulseless VT/VF persist s, t hen CPR should be perf ormed f or 1 minut e prior t o reassessment of t he rhyt hm and

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pulse. If pulseless VT/VF persist s, t hree f urt her shocks at 360 J each are administ ered.

Cardiovascular System

Amiodarone is now t he ant iarrhyt hmic drug of choice f or shock-resist ant pulseless VT/VF. It can be administ ered in a dose of 300 mg af t er t he t hird unsuccessf ul shock. SCC pp 11–15

A 72. A. t rue

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E. t rue

During cardiopulmonary resuscit at ion, t he circulat ion t ime f rom t he cent ral veins t hrough t he heart t o t he f emoral art eries is approximat ely 30 seconds compared w it h up t o 5 minut es w hen a peripheral vein is used. Drug delivery during cardiac arrest is t heref ore opt imally achieved via a cent ral vein. Obt aining cent ral venous access in t he set t ing of a cardiac arrest , how ever, requires considerable skill and peripheral access may have t o be accept ed.

Answ ers

Epinephrine (adrenaline) 1 mg should be administ ered every 3 minut es during cardiopulmonary resuscit at ion. It causes vasoconst rict ion and increases cerebral and coronary perf usion. Open chest cardiac massage (resuscit at ive t horacot omy) is indicat ed f ollow ing recent cardiot horacic surgery, in pulseless elect rical act ivit y (PEA) f ollow ing penet rat ing t rauma, in pat ient s w it h hyperinf lat ed lungs or a f ixed rib cage w here ext ernal chest compression is not possible, and during abdominal or t horacic surgery. SCC pp 11–15

A 73. A. f alse

B. f alse

C. t rue

D. f alse

E. t rue

When peripheral or cent ral access cannot be gained rapidly, t he t racheal rout e can be used f or t he administ rat ion of cert ain drugs. These include epinephrine (adrenaline), at ropine, lidocaine (lignocaine), naloxone and vasopressin. The dose of t he drug should be increased t o 2–3 t imes t hat of t he int ravenous dose. Calcium salt s, sodium bicarbonat e and amiodarone are not suit able f or t racheal administ rat ion. SCC pp 11–15

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A 74. A. t rue

B. t rue

C. t rue

D. f alse

E. t rue

M CQs

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Answ ers

SCC pp 11–15

Cardiovascular System

PEA w as f ormerly know n as elect romechanical dissociat ion (EM D). It is charact erised by cardiac arrest w it h an ECG rhyt hm, ot her t han VT, compat ible w it h a cardiac out put (cardiac arrest w it h VT is pulseless VT and is managed as VF w it h def ibrillat ion). The ALS algorit hm is t he same f or asyst ole and PEA, so f or t he purposes of management t hey are grouped t oget her as non-VF/VT. Non-VF/VT rhyt hms carry a w orse prognosis t han pulseless VT/VF unless a reversible cause can be ident if ied and t reat ed. Cardiopulmonary resuscit at ion is perf ormed w hile t he recognised causes of PEA are sought . These include t he 4 ‘Hs’ and t he 4 ‘Ts’: hypoxia, hypovolaemia, hypot hermia, and hypo/hyperkalaemia and ot her met abolic disorders, t ension pneumot horax, cardiac t amponade, t hromboembolic circulat ory obst ruct ion (massive PE), and t oxic/t herapeut ic subst ances e.g. calcium channel blocker and ␤-blocker overdose. During cardiopulmonary resuscit at ion, epinephrine 1 mg should be administ ered every 3 minut es. In PEA, at ropine 3 mg should be administ ered only if t he heart rat e on ECG is ⬍60/minut e.

89

Respiratory System A 1.

A. t rue

B. f alse

C. t rue

Answ ers

D. t rue

E. t rue

Posit ive end expirat ory pressure (PEEP) increases: Funct ional residual capacit y (FRC), int ra-cranial pressure (ICP) compliance, and barot rauma. SCC p 84, p 94

A 2.

A. t rue

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C. t rue

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E. t rue

The f eat ures are respirat ory rat e (RR) ⬎ 30 breat hs per minut e, O2 sat urat ion ⬍ 80% , PaO2 ⬍ 8 KPa, PaCO2 ⬎ 7 kPa, dyspnoea, increasing dist ress, exhaust ion, sw eat ing, conf usion, vit al capacit y ⬍ 15 ml/kg, FEV1 (f orced expirat ory volume) ⬍ 10 ml/kg. SCC pp 79–80

A 3.

A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Hyponat raemia can occur w it h low, normal or high ext racellular f luid (ECF) volume. Urine sodium levels help dist inguish bet w een t he causes. SCC p 157

A 4.

A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

All t he above plus pneumat oceles, ret roperit oneal air and acut e lung injury (ALI). SCC pp 80–86

A 5.

A. f alse

B. t rue

C. t rue

D. t rue

E. t rue

Hypert hyroidism rat her t han hypot hyroidism can cause respirat ory alkalosis. The remainder all can. SCC pp 74–75

90

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A 6.

A. f alse

B. t rue

C. t rue

D. t rue

E. f alse

A 7.

A. t rue

B. t rue

C. t rue

D. t rue

Answ ers

SCC pp 91–96

Respiratory System

Adult respirat ory dist ress syndrome (ARDS) is charact erised by respirat ory f ailure, diff use alveolar inf ilt rat es on chest X-ray, and a normal or low pulmonary art ery occlusion pressure (PAOP). The lat t er qualif icat ion diff erent iat es t he condit ion f rom cardiogenic pulmonary oedema. ARDS has many possible causes t hat include sept icaemia, cardio-pulmonary bypass, acut e pancreat it is, f at embolism, t rauma, burns, smoke inhalat ion, placent al abrupt ion and amniot ic f luid embolism. ARDS ref lect s a syst emic inf lammat ory response t hat is usually associat ed w it h mult iorgan dysf unct ion. There is a generalised increase in vascular permeabilit y mediat ed by inf lammat ory cyt okines. In t he lung, t his is ref lect ed by alveolar inf ilt rat es comprising f ibrin, plat elet s and inf lammat ory cells. Subsequent f ibroblast act ivat ion result s in pulmonary f ibrosis. M anagement is support ive w hile t he underlying cause, most commonly sepsis, is t reat ed. Vent ilat ory support is required. Volume overload should be avoided. There is no evidence t hat st eroids improve prognosis in ARDS. Prost acyclin reduces pulmonary art ery pressures, but it s role in t he management of ARDS remains t o be est ablished. Prone vent ilat ion may improve oxygenat ion.

E. t rue

Respirat ory f ailure is def ined by a PaO2 ⬍ 8 kPa and is divided int o t ype I w hen t he PaCO2 is normal or low, and t ype II w hen t he PaCO2 is raised. A number of condit ions may cause respirat ory f ailure in t he post -operat ive period. Whet her or not respirat ory f ailure occurs depends upon t he severit y of t he condit ion e.g. pneumonia, and t he pre-exist ing lung f unct ion. Those w it h pre-exist ing abnormal lung f unct ion, most commonly due t o chronic obst ruct ive pulmonary disease (COPD), are more likely t o develop post -operat ive respirat ory f ailure since t hey have less reserve. The commonest post -operat ive respirat ory complicat ion is basal at elect asis. This occurs due t o inadequat e vent ilat ion and expect orat ion result ing in ret ained secret ions due t o pain, and diaphragmat ic splint ing due t o ileus. It may become complicat ed by superadded inf ect ion. Prevent ion f ocuses on adequat e analgesia and physiot herapy.

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Opiate analgesia may result in (type II) respiratory failure through depression of the respiratory centre. Pulmonary embolism usually causes type I respiratory failure as PaCO2 is low due to hyperventilation to compensate for hypoxia. ARDS may complicate any major surgery, particularly after cardio-pulmonary bypass.

Respiratory System

SCC pp 79–80

A 8.

A. f alse

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Answ ers

Cent ral chemorecept ors are locat ed close t o t he f loor of t he f ourt h vent ricle, near t he respirat ory cent re in t he brainst em. They are sensit ive t o pH change in t he cerebrospinal f luid (CSF) t hat surrounds t hem. Hydrogen (H⫹) and bicarbonat e (HCO⫺ 3) diff use slow ly bet w een blood and CSF, CO2 how ever moves f reely CSF is low in prot ein and buff ering capacit y is poor. Theref ore relat ively lit t le increase in CO2 levels have a prof ound eff ect on CSF pH. This pH change is det ect ed by t he cent ral chemorecept ors and inf ormat ion relayed t o t he respirat ory cent re t o increase (f or ↑ CO2) or decrease (f or ↓ CO2) t he rat e and dept h of breat hing. CO2 changes in t he CSF is event ually buff ered by t he slow diff usion of HCO⫺ 3 across t he blood brain barrier. SCC p 60

A 9.

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C. t rue

D. f alse

E. t rue

Peripheral chemorecept ors are sensit ive t o O2 and are f ound in t he carot id and aort ic bodies. The out put f rom peripheral chemorecept ors increases w it h hypoxia dow n t o PaO2 4.4 kPa, below w hich it remains const ant but does not st op. The combined eff ect s of hypercabia and hypoxia are summat ive cent ral chemorecept ors are locat ed in t he vent ral medulla. The Hering-Breuer ref lex is prot ect ive and prevent s damage due t o volut rauma and barot rauma, by limit ing maximal inspirat ion. SCC p 60

A 10. A. f alse

B. t rue

C. f alse

D. f alse

E. f alse

Tot al lung capacit y is t he t ot al volume of air in t he lungs at t he end of a maximal inspirat ion. The expirat ory reserve volume is 92

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Key Quest ions in Surgical Crit ical Care

SCC pp 61–62

A 11. A. f alse

B. f alse

C. t rue

D. t rue

E. f alse

SCC pp 61–62

A 12. A. f alse

B. t rue

C. f alse

D. t rue

Answ ers

FRC is t he volume of air remaining in t he lung af t er t idal expirat ion, and is usually 2.2 lit res in adult s. It s import ance is as a source of oxygen reserve, w hich can cont inue t o t ake place in gaseous exchange bet w een breat hs. The relat ionships bet w een FRC and closing capacit y is import ant since t he air mixt ure in t he FRC can only t ake place in gaseous exchange if t he airw ays are given. Reducing FRC compared w it h closing capacit y t heref ore leads t o hypoxaemia. All manoeuvres t hat increase lung volume w ill improve FRC. Regional anaest hesia does not increase FRC per se but prevent s t he f urt her decrease seen w it h general anaest hesia.

Respiratory System

usually 1 lit re in adult s. Closing capacit y is t he lung volume w here small airw ays begin t o collapse on expirat ion. If t his f alls below FRC during t idal (normal) vent ilat ion t hen it w ill result in hypoxaemia. Tot al lung capacit y is t he combinat ion of vit al capacit y and residual volume, irrespect ive of at mospheric pressure.

E. f alse

Respirat ory compliance is t he change in volume (l) per unit change in pressure (kPa). It gives an indicat ion of t he amount of w ork required t o expand t he lungs during inspirat ion. The charact erist ic sigmoid shaped compliance curve suggest s t hat compliance is decreased at ext remes of lung volume i.e., low and high lung volumes. Compliance is reduced at t he ext remes of age, in t he new born because of t he increased t endency f or t he lung t o collapse, and in t he elderly because of reduced t issue elast icit y. Compliance is reduced by rest rict ive and obst ruct ive lung disease. SCC pp 62–64

A 13. A. f alse

B. f alse

C. t rue

D. f alse

E. f alse

During spont aneous vent ilat ion t he majorit y of t he inspired gas is direct ed t o t he low er (dependent ) part s of t he lungs. This is

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because of t he great er negat ive pressure generat ed at t he base. Compliance is great est (i.e. st eepest part of t he curve) in t he middle zones (w est zones 2 and 3) during spont aneous vent ilat ion. Wit h mechanical vent ilat ion inspired gas is direct ed pref erent ially t ow ards t he upper (non-dependent ) areas of t he lungs w here compliance is now great est . M ore w ork is required t o dist end t he low er (w est zone 4) areas of t he lung w it h posit ive pressure vent ilat ion, hence t hey are show n as f lat port ions of t he sigmoid shaped compliance curve. Hypoxic pulmonary vasoconst rict ion (HPV) is a met hod w hereby blood is direct ed aw ay f rom under vent ilat ed areas of t he lung, reducing t he pot ent ial f or shunt , and hence hypoxaemia. SCC p 65

A 14. A. f alse

B. f alse

C. f alse

D. t rue

E. f alse

Answ ers

Shunt ref ers t o areas of t he lung w hich are w ell perf used but poorly vent ilat ed. Dead space ref ers t o areas of t he lung w hich are w ell vent ilat ed but poorly perf used. Bot h lead t o art erial hypoxaemia. The art erial hypoxaemia of shunt cannot be correct ed by increasing t he inspired oxygen concent rat ion alone since t he aff ect ed areas are poorly vent ilat ed, hence t he increased oxygen concent rat ion does not come int o cont act w it h blood. Blood supply decreases f rom t he bot t om t o t he t op of t he lung. Vent ilat ion also decreases but t o a lesser degree. This leads t o t he t endency f or t he upper part s of t he lung t o develop increased dead space and low er (dependent ) part s of t he lung t o develop increased shunt . The opt imal part of t he lung f or gaseous exchange is t heref ore t he mid port ion (w est zones 2 and 3). SCC p 65

A 15. A. f alse

B. f alse

C. t rue

D. f alse

E. f alse

FEV1/FVC rat io is usually 0.8. The rat io is usually increased in rest rict ive condit ions since t he FVC is of t en reduced t o a larger degree t han t he FEV1. The rat io is decreased in obst ruct ive condit ions since t he FVC remains largely const ant but t he FEV1 is of t en severely reduced. Bot h rest rict ive and obst ruct ive condit ions may be diagnosed but t he result s depend on t he overall clinical pict ure and t he t echnique of t he pat ient in obt aining t he dat a. Rest rict ive condit ions can give a normal 94

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rat io but t he absolut e values are usually below t he normal range f or sex, height and w eight . Pulmonary f unct ion t est s are usually carried out in a laborat ory w it h t he use of a spiromet er. Peak f low met ers are a bedside t est t o monit or t reat ment .

A 16. A. t rue

B. f alse

C. f alse

D. f alse

E. t rue

The normal range f or PaCO2 is 4.4–5.8 kPa. The normal range f or PaO2 (breat hing room air) is 10–13 kPa. pH is indirect ly proport ional t o t he H⫹ cont ent of blood (negat ive logarit hm). St andard bicarbonat e (SBC) is a measure of plasma HCO⫺ 3 correct ed t o a PaCO2 of 5.3 kPa, t hus removing t he inf luence of any respirat ory eff ect s. Decreasing t he t emperat ure of a sample decreases t he pH and oxygen cont ent , t heref ore t he H⫹ cont ent increases w it h decreasing t emperat ure. Normal pH at 27⬚C is 7.25.

Respiratory System

SCC pp 65–67

SCC pp 67–75

B. f alse

C. f alse

D. f alse

E. f alse

Homeost asis involves t he maint enance of const ant pH, w hich is essent ial f or cellular f unct ion. Acidosis and alkalosis leads direct ly t o cellular dysf unct ion and end organ damage. The bicarbonat e buff er syst em:

Answ ers

A 17. A. f alse

H2O + CO2 ⇌ H2 CO3 ⇌ H+ + HCO 3−

account s f or over t w o t hirds of t he body’s buff ering capacit y. This is an open buff er syst em since t he component s can be varied independent ly of each ot her (CO2 by t he lungs and HCO⫺ 3 by t he kidneys). Deoxygenat ed haemoglobin has great er buff ering capacit y t han t he oxygenat ed f orm. Full compensat ion of acid-base imbalance w ill result in ret urn t o normal values and does not result in over correct ion (unless t here is anot her pat hological process occurring). SCC pp 67–75

A 18. A. t rue

B. f alse

C. f alse

D. f alse

E. t rue

M et abolic acidosis result s f rom increased H⫹ levels or decreased HCO⫺ 3 levels. The commonest causes are lact ic or ket o acidosis,

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95

Respiratory System

renal f ailure and diarrhoea. Alt hough blood HCO⫺ 3 levels are low sodium bicarbonat e is reserved f or severe or unresponsive cases only. Sodium bicarbonat e can lead t o w orsening int racellular acidosis and present s a large sodium and carbon dioxide load, of t en in sit uat ions w hen t he body’s excret ory mechanisms are over st ret ched. The main goal of t herapy is t reat ment of t he underlying cause and re-hydrat ion. Normal compensat ion is by hypervent ilat ion. Salicylat e poisoning can lead t o a mixed pict ure of met abolic acidosis and respirat ory alkalosis. SCC pp 69–71

A 19. A. f alse

B. f alse

C. f alse

D. t rue

E. t rue

Answ ers

This is t he clinical pict ure of diabet ic ket o acidosis. The met abolic acidosis exist s because of t he build up of acid in t he f orm of ket ones. This is a lif e t hreat ening condit ion and t he primary concern is t o rehydrat e t he pat ient w it h normal saline. As a result of polyuria in t he init ial st ages caused by an osmot ic diuresis, t he pat ient may be severely dehydrat ed and require upt o 10 lit res of f luid resuscit at ion. Cont rol of blood sugar is secondary and should be done gradually. Urine out put should be monit ored caref ully. SCC pp 69–71

A 20. A. t rue

B. t rue

C. t rue

D. f alse

E. t rue

This is t he clinical pict ure of met abolic alkalosis. The main causes are loss of H⫹ f rom t he kidneys e.g. diuret ic t herapy, hypokalaemia or mineralocort icoid excess; or H⫹ loss f rom t he gut e.g. vomit ing. Compensat ion is by hypovent ilat ion w hich may result in hypoxia. Normal saline may be indicat ed f or hypochloraemic hypovolaemia associat ed w it h vomit ing. Urine pH is usually alkaline t o prevent f urt her loss of H⫹. SCC pp 71–72

A 21. A. f alse

B. f alse

C. f alse

D. t rue

E. f alse

Respirat ory acidosis w it h ast hma is a grave sign and may herald respirat ory arrest . Airw ay ⫹ Breat hing are of primary concern in all pat ient s. In t rauma cases t he airw ay should be secured if t here is any doubt about t he pat ency or t he mechanism f or vent ilat ion. 96

M CQs

Key Quest ions in Surgical Crit ical Care

SCC pp 72–73

A 22. A. t rue

B. t rue

C. f alse

D. f alse

E. f alse

Answ ers

Early pneumonia and ARDS of t en result s in respirat ory alkalosis, w hich may become acidosis as t he clinical condit ion w orsens. Respirat ory alkalosis is usually driven by hypoxia and t heref ore oxygen t herapy is essent ial w hilst w orking out t he cause. Oxygen t herapy may w ell reverse t he respirat ory alkalosis by reducing respirat ory drive. When occurring in pat ient s w it h know n deep vein t hrombosis (DVT) may herald a pulmonary embolus, w hich can be f at al. The normal compensat ory mechanism is t o preserve H⫹ ions and t heref ore produce an alkaline urine.

Respiratory System

Failure t o correct airw ay or breat hing insuff iciency early may lead t o diff icult y lat er (of t en w hen pat ient s, have been moved t o less well monitored areas e.g., CT scan). Sodium bicarbonate increases the CO2 burden and compounds the problem. Pre-existing compensat ed respirat ory acidosis (due t o CO2 ret ent ion e.g. in COPD pat ient s) can lead t o normal pH w it h elevat ed PaCO2. HCO⫺ 3 f ormed f rom CO2 is neut ralized by t he bicarbonat e buff er syst em, t he increased H⫹ is excret ed in t he urine.

SCC pp 74–75

A 23. A. t rue

B. f alse

C. f alse

D. t rue

Oxygen delivery DO 2 = CO × [(Hb ×

Sat

E. f alse 100

× 1.34) + (PaO2 × 0.003) ]

Alt hough Hb 15 g/dl carries more oxygen t han Hb 10 g/dl t he reduced viscosit y of t he lat t er aff ords more eff icient delivery t o t he t issues. Oxygen delivery is reduced at alt it ude because of reduced part ial pressure of t he inspired air, despit e t he f act t hat cardiac out put (CO) great ly increases. Because t he vast majorit y of t he oxygen carrying capacit y is due t o it s combinat ion w it h haemoglobin, increasing t he inspired oxygen concent rat ion w ill have lit t le ext ra eff ect on oxygen delivery providing t hat haemoglobin is already f ully sat urat ed w it h O2. The dissolved f ract ion is usually negligible and rises relat ively lit t le w it h increased O2 concent rat ion in t he inspired air. SCC pp 76–78

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Key Quest ions in Surgical Crit ical Care

97

A 24. A. f alse

B. f alse

C. f alse

D. t rue

E. t rue

Respiratory System

Carbon monoxide poisoning causes anaemic hypoxia since it s high aff init y f or haemoglobin prevent s t he usual binding of oxygen molecules. St agnant hypoxia is due t o low CO st at es and causes high oxygen ext ract ion leading t o a low er venous oxygen cont ent . Conversely high venous oxygen cont ent may be seen in condit ions w it h hyperdynamic circulat ions such as sepsis. Alt it ude and cyanot ic heart disease result in hypoxic hypoxia result ing in reduced haemoglobin sat urat ion and low oxygen part ial pressure in blood. SCC pp 76–77

A 25. A. f alse

B. f alse

C. f alse

D. t rue

E. f alse

Answ ers

Post -operat ive shivering is problemat ic because t he increased muscle movement great ly elevat es t he body’s oxygen requirement s. Oxygen t herapy is given t o sat isf y t he increased needs of t he body and not t o st op t he shivering. The Hudson mask is a variable perf ormance oxygen delivery syst em w here t he oxygen concent rat ion depends on t he pat ient ’s minut e volume and peak inspirat ory f low rat e (PIFR). At high PIFR room air is ent rained leading t o a reduct ion in oxygen concent rat ion delivered t o t he pat ient . 10 l/min via t he Hudson mask gives an oxygen concent rat ion of 61–73% . SCC pp 77–78

A 26. A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

Vent uri masks deliver a const ant oxygen concent rat ion independent of t he pat ient s respirat ory pat t ern (minut e volume and PIFR). The oxygen supply ent rains air at a f ixed rat e via a jet built int o t he mask. These masks, unlike Hudson masks are colour coded: w hit e (28% ), yellow (35% ), red (40% ) and green (60% ). Vent uri masks are used w hen pat ient s require know n concent rat ions of oxygen e.g. COPD pat ient s. Hudson masks are a simpler design and t end t o be used f or rout ine post -operat ive use. Vent uri masks are less eff icient t han Hudson masks since t hey only ent rain a cert ain amount of room air. SCC p 78

98

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A 27. A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

Respiratory System

In t ype I respirat ory f ailure t here is hypoxaemia w it h low or normal PaCO2. In Type II respirat ory f ailure t here is hypoxaemia w it h hypercarbia, leading t o respirat ory acidosis. Type I f ailure may be due t o early pneumonia or ARDS w it h hypoxaemia being t he precipit ant f or increased respirat ory eff ort result ing in a respirat ory alkalosis. As t hese diseases progress, so t he pat ient is more likely t o develop t ype II f ailure as t hey get exhaust ed or because of an increased diff usion barrier f or gaseous exchange in t he lungs. Guillain Barré is a neuromuscular condit ion believed t o be immunologically mediat ed. This result s in a f laccid paralysis of t he body, including t he respirat ory muscles leading t o a mechanical f ailure of vent ilat ion and t ype II f ailure. SCC pp 79–80

A 28. A. f alse

B. f alse

C. f alse

D. f alse

E. t rue

Answ ers

Whilst bot h t ypes of respirat ory f ailure are serious condit ions requiring urgent medical at t ent ion, t ype I f ailure is usually driven by hypoxaemia and is associat ed w it h less mechanical diff icult y in vent ilat ion. Correct ion of t he hypoxia w ill provide t ime f or diagnosis and clinical priorit isat ion. Type II f ailure of t en requires immediat e act ion t o prevent severe vent ilat ory compromise or even respirat ory arrest . In some inst ances (but not alw ays) t ype I may be t hought of as an earlier st age t han t ype II. Kyphoscoliosis t ends t o be a mechanical vent ilat ory f ailure leading t o t ype II respirat ory f ailure. Alt hough pat ient s w it h t ype II f ailure have t achypnoea t heir vent ilat ory excursion is usually inadequat e, leading t o CO2 ret ent ion. Flail chest leads t o mechanical f ailure of vent ilat ion (t ype II). SCC pp 79–80

A 29. A. f alse

B. f alse

C. f alse

D. f alse

E. t rue

Cyanosis is t he blue discolourat ion of t he skin caused by t he presence of great er t han 5 g/dl of deoxyhaemoglobin. It is possible t o have cyanosis w it hout hypoxia in polycyt haemic pat ient s and hypoxia w it hout cyanosis in anaemic pat ient s. A low ered level of consciousness is not a reliable sign of respirat ory dist ress per se, but in combinat ion w it h ot her signs suggest s a severe level of hypoxia. Head injuries may lead t o t achypnoea and loss of

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99

Respiratory System

consciousness w it hout respirat ory f ailure. Tachypnoea is also associat ed w it h hypovolaemia and t he compensat ion f or met abolic acidosis. Tachycardia is associat ed w it h a mult it ude of clinical sit uat ions unrelat ed t o respirat ory f ailure. The appearance of int ercost al or subcost al recession and t racheal t ug are pret t y specif ic signs of respirat ory f ailure w it h t he body using every possible mechanical advant age t o improve vent ilat ion. SCC pp 79–80

A 30. A. f alse

B. t rue

C. f alse

D. f alse

E. f alse

Answ ers

The decision t o inst it ut e respirat ory support is of t en complicat ed and dependent on several f act ors. The PaO2 should be less t han 8 kPa on 60% oxygen (not 40% ). The PaCO2 level w ill depend on t he pat ient ’s pre-morbid level and t he use of a general ‘cut -off ’ f igure f or every pat ient is not helpf ul. How ever f or pat ient s w it hout a previous hist ory of respirat ory f ailure or hypercapnoea a PaCO2 above 8 kPa is usually t aken as signif icant . Prot ect ion of t he low er airw ay should be inst it ut ed in pat ient s w it h a Glasgow coma score (GCS) less t han 8, t his w ill usually also require mechanical vent ilat ion. The presence of a t racheost omy is not an indicat ion f or respirat ory support in it self . SCC pp 80–87

A 31. A. f alse

B. t rue

C. f alse

D. t rue

E. t rue

Expirat ion is passive in spont aneous and mechanical vent ilat ion. Pneumot horacies should alw ays be drained prior t o int ermit t ent posit ive pressure vent ilat ion (IPPV), since t here is a signif icant risk of causing t ension pneumot horax by increasing t he int ra-t horacic pressure. HPV is reduced by bot h IPPV and anaest hesia, increasing t he risk of shunt and hypoxaemia. Blood pressure may init ially increase due t o t he increase in int ra-t horacic pressure. Acid/base dist urbances may result f rom under or over vent ilat ion. SCC pp 81–82

A 32. A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

IPPV reduces venous ret urn by increasing int ra-t horacic pressure. The negat ive int ra-t horacic pressure of spont aneous vent ilat ion 100

M CQs

Key Quest ions in Surgical Crit ical Care

SCC pp 81–82

A 33. A. f alse

B. f alse

C. f alse

D. t rue

Respiratory System

act s t o ‘pump’ blood back t o t he heart . Sedat ion is usually required since t he pat ient is of t en int ubat ed, w hich is st imulat ing t o t he gag ref lex. Blood pressure may be reduced on correct ion of acidosis because of low ering endogenous adrenaline levels. Hypercarbia is associat ed w it h cat echolamine release and hypert ension and t achycardia. Glomerular f ilt rat ion rat e is decreased as a result of reduced renal blood f low and CO. The rise in int ra-t horacic pressure is t ransmit t ed via t he venous syst em t o increased int ra-cranial pressure. This is of t en off set how ever, by t he abilit y t o cont rol CO2 levels and hence int ra-cranial volume.

E. f alse

Answ ers

FIO2 is the fractional inspired oxygen concentration and should be set to 0.5 (50%) initially. Subsequent adjustment will depend on frequent arterial blood gas sampling. In extreme circumstances the FIO2 may be set to 1.0 but this increases the risk of absorption atelectasis and lung collapse. Tidal volume is usually set at 10–12 ml per kg. Oxygen is mixed with air to prevent absorption atelectasis in the intensive care unit (ICU) since nitrous oxide is an anaesthetic. The nitrogen in air being inert is not absorbed in the lungs, thus ‘splinting’ them open. Asthmatics require longer expiratory times due to the obstructive nature of the condition. PEEP has a number of side effects, mainly on decreasing venous return and is not applied unless required. SCC pp 81–82

A 34. A. t rue

B. f alse

C. f alse

D. f alse

E. t rue

The vent ilat or w ill deliver a set t idal volume at a set RR. The pat ient is usually sedat ed and paralysed w it h muscle relaxant and makes no respirat ory eff ort . Peak pressure w ill depend on t he pat ient ’s respirat ory compliance. As compliance reduces so t he peak pressure w ill increase, and enhances t he risk of damage t o t he lungs by barot rauma. This is t heref ore not a usef ul mode of vent ilat ion f or pat ient s w it h poor compliance. Since t he pat ient is sedat ed and paralysed t his mode of vent ilat ion is not suit able f or w eaning. SCC pp 83–87

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101

A 35. A. t rue

B. f alse

C. f alse

D. t rue

E. t rue

Respiratory System

M inut e volume is made up of a mixt ure of mandat ory breat hs init iat ed by t he vent ilat or and spont aneous breat hs init iat ed by t he pat ient . This leads t o an inconsist ency of volume bet w een cycles. Spont aneous and mandat ory (machine) breat hs are synchronised so t hat t he machine breat hs can only be delivered w hen t he pat ient is not t aking a spont aneous breat h. This prevent s high peak airw ay pressures and t he risk of barot rauma. This is a w eaning mode and t heref ore muscle relaxat ion is count er-product ive, also t he pat ient must be able t o init iat e a breat h. The mixt ure of spont aneous and mechanical breat hs allow s a more f avourable vent ilat ion t o perf usion prof ile t han cont rolled mandat ory vent ilat ion (CM V) w hich result s in much higher int ra-t horacic pressures. SCC pp 83–87

A 36. A. f alse

B. f alse

C. t rue

D. f alse

E. t rue

Answ ers

Pressure cont rolled vent ilat ion (PCV) is used w hen pulmonary compliance is low. The peak pressure and RR are set on t he vent ilat or and t he minut e volume delivered t o t he pat ient w ill depend on t he compliance. Because of t he square w ave pressure t race t he result ant mean airw ay pressure (M AWP) is higher t han t he CM V t race f or any given peak airw ay pressure. Since M AWP equat es w it h oxygenat ion, PCV t heref ore result s in improved oxygen delivery. M uscle paralysis is of t en required as t he pat ient is f ully vent ilat ed and spont aneous act ivit y is not encouraged. SCC pp 83–87

A 37. A. f alse

B. t rue

C. f alse

D. f alse

E. f alse

Pressure support vent ilat ion (PSV) is a w eaning mode t hat requires t he pat ient s t o be complet ely unparalysed, since t hey init iat e all of t he delivered breat hs. A level of pressure support is set on t he vent ilat or and t he t idal volume delivered t o t he pat ient w ill depend on t heir lung compliance. The vent ilat or does not init iat e any of t he breat hs delivered. Sedat ion is somet imes required because t he pat ient may st ill be int ubat ed, w hich st imulat es t he gag ref lex. The level of respirat ory support 102

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may be reduced as w eaning progresses unt il t he pat ient can breat h spont aneously unaided. SCC pp 83–87

B. t rue

C. f alse

D. f alse

E. t rue

PEEP is used t o prevent collapse of t he airw ay, w hich leads t o hypoxia, during vent ilat or delivered breat hs. Cont inuous posit ive airw ays pressure (CPAP) is used f or spont aneous breat hs in bot h int ubat ed (including t racheost omies) and unint ubat ed subject s. Bot h PEEP and CPAP reduce venous ret urn and consequent ly reduce CO and blood pressure. Inverse rat io vent ilat ion (IRV) is used t o recruit collapsed alveoli in pat ient s on PCV. Expirat ion is alw ays passive. Since t he t ime allow ed f or expirat ion is great ly reduced, respirat ory acidosis can occur as t he CO2 rises. This can be an ext remely unst able mode of vent ilat ion cardiovascularly since t here is lit t le t ime f or venous ret urn during expirat ion.

Respiratory System

A 38. A. f alse

SCC pp 80–87

B. t rue

C. f alse

D. f alse

E. f alse

If t he pat ient cont inues t o need opioids f or pain management or t o t olerat e t he endo-t racheal t ube (ETT) t hen t hey should cont inue. PCV is not an easy mode t o w ean f rom since t he pat ient s usually require a large amount of support – but it can be done. Pat ient s should be put ont o a T-piece, w hich off ers no prot ect ion against airw ay collapse and no pressure support w hen t he synchronised int ermit t ent mandat ory vent ilat ion (SIM V) rat e is zero, pressure support 10 cmH2O and PEEP 5 cmH2O. When a pat ient f irst goes ont o a T-piece it may be desirable t o alt ernat e t his w it h periods on t he vent ilat or t o maint ain alveolar recruit ment and prevent collapse.

Answ ers

A 39. A. f alse

SCC pp 85–87

A 40. A. f alse 䊏 䊏 䊏 䊏

M CQs

B. t rue

The correct The correct The correct The correct (f emale)

C. f alse

D. f alse

E. t rue

lengt h f or a paediat ric ETT is age/2 ⫹ 12 cm diamet er f or a paediat ric ETT is age/4 ⫹ 4 cm diamet er f or an adult f emale is 7.5–8 mm lengt h f or adult s is 23 cm (male) and 21 cm

Key Quest ions in Surgical Crit ical Care

103

Respiratory System

Cricoid pressure is also know n as Sellicks manouvre and is applied w it h a f orce of 40 New t ons vert ically dow nw ard on t he cricoid cart ilage. One or t w o hands may be used and it s purpose is t o prevent gast ric aspirat ion during induct ion of anaest hesia as part of a rapid sequence induct ion t echnique. This t echnique is employed in all sit uat ions w here a f ull st omach is suspect ed e.g. emergency surgery or t rauma. SCC pp 90–91

A 41. A. f alse

B. t rue

C. f alse

D. t rue

E. f alse

Answ ers

Nasal int ubat ion is mainly pract iced in children an ICU. Nasal int ubat ion is bet t er t olerat ed t han oral and does not st imulat e t he gag ref lex t o such a large ext ent . Sedat ion requirement s are t heref ore much reduced in t his group of pat ient s. Nasal int ubat ion requires laryngoscopy just as oral int ubat ion does and is t heref ore just as cardiovascularly st imulat ing. Tracheost omy is indicat ed f or prolonged w eaning or vent ilat ion and f acilit at es cont inued prot ect ion of t he airw ay in pat ient s, w it h impaired pharyngeal ref lexes or conscious level. Tracheost omy is not indicat ed primarily f or obesit y, alt hough obese pat ient s may f all int o t he group t hat have prolonged vent ilat ion and w eaning. There may be t echnical diff icult ies in securing a t racheost omy in obese pat ient s. SCC pp 87–91

A 42. A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

ARDS is t he pulmonary component of t he syst emic inf lammat ory response syndrome (SIRS). It is essent ially an inf lammat ory response t o a subst ant ial insult . The commonest causes are sepsis and t rauma bot h pulmonary and ext ra-pulmonary. Ot her common causes are pancreat it is, haemorrhage and shock, gast ric aspirat ion and associat ed w it h massive blood t ransf usion. Raised int ra-cranial pressure leads t o neurogenic pulmonary oedema w hich alt hough giving a similar clinical pict ure t o ARDS has a diff erent pat hological process. SCC pp 91–96

104

M CQs

Key Quest ions in Surgical Crit ical Care

A 43. A. f alse

B. f alse

C. f alse

D. f alse

E. f alse

A recent consensus conf erence has based t he def init ion of ARDS on t he presence of t he f ollow ing crit eria:

Alt hough it is likely t hat t he pat ient w ill require mechanical vent ilat ion and t hat t hey usually have high airw ay pressures, t his does not f orm part of t he def ining crit eria. In ARDS t he PaO2 : FIO2 rat io is ⬍40 kPa, but in ALI, a less severe illness t he PaO2 : FIO2 rat io is ⬎27 kPa, signif ying less hypoxaemia.

Respiratory System

I. There must be a know n precipit at ing cause II. The onset of sympt oms must be acut e III. There must be new bilat eral f luff y inf ilt rat es on t he CXR (t his may lag behind t he clinical pict ure by 12–24 hours) IV. There must be no cardiac f ailure or f luid over load (peak airw ay pressure (PAWP) must be ⬍18 mmHg)

SCC pp 91–96

B. f alse

C. t rue

D. f alse

E. f alse

The inf lammat ory response releases mediat ors such as cyt okines, t umour necrosis f act or (TNF), plat elet act ivat ing f act or (PAF) and int erleukin (IL). These cause capillary endot helial damage leading t o increased permeabilit y and a prot ein rich exudat e f ills t he alveoli. This result s in at elect asis and collapse leading t o art erial hypoxaemia. Lat e f eat ures are f ibroblast prolif erat ion leading t o f ibrosis and collagen deposit ion result ing in microvascular oblit erat ion. A f ibrosing-alveolit is pict ure may be seen in some pat ient s but t his is a lat e development .

Answ ers

A 44. A. t rue

SCC pp 91–96

A 45. A. f alse

B. f alse

C. f alse

D. t rue

E. f alse

Fluids should be given judiciously since t he hypoxaemia may be made w orse by f urt her alveolar oedema. Concurrent sepsis or hypovolaemia has t o be addressed but caref ul monit oring of cent ral pressures should be observed. A PAFC may be usef ul f or f luid management but is not essent ial in t he t reat ment of ARDS, t he management of w hich is largely support ive. PAFC’s do have an inherent morbidit y and mort alit y at t ached t o t heir insert ion

M CQs

Key Quest ions in Surgical Crit ical Care

105

Respiratory System

and should be used only w hen required. The basis of t he respirat ory support should be t o prevent f urt her harm t o t he good (unaff ect ed) part s of t he lung w hilst support ing t he damaged part s. Theref ore moderat e hypoxaemia (PaO2 ⬎ 8 kPa) and permissible hypercapnoea (PaCO2 10–15 kPa) may be t olerat ed if t here is no cerebral oedema, acidosis or cardiovascular compromise. High peak airw ay pressures are avoided t o prot ect t he lung. SCC pp 91–96

A 46. A. f alse

B. t rue

C. t rue

D. f alse

E. f alse

Answ ers

PEEP is usually required t o move t he low er part of t he compliance curve t o a more f avourable (st eeper part of t he curve) posit ion. PEEP prevent s t he collapse of recruit ed alveolar unit s in t he lung, so reducing hypoxaemia. FRC act s as an oxygen st ore and w hen increased improves oxygenat ion. IRV increases M AWP w hich opt imises oxygenat ion but reduces CO2 removal because of t he reduced expirat ory t ime, t heref ore overall gas exchange is not opt imised. Nit ric oxide is also know n as endot helial derived relaxant f act or and is a pot ent vasodilat or. When given by nebuliser it passes t o t hose ‘healt hy’ unaff ect ed lung unit s and improves t he bloodf low t hus reducing dead space and improving hypoxia. If given int ravenously how ever it has a general eff ect , w orsening shunt in areas of t he lung t hat are damaged and t heref ore perf used but not adequat ely vent ilat ed. SCC pp 91–96

A 47. A. f alse

B. f alse

C. t rue

D. t rue

E. f alse

Prognosis is aff ect ed by increasing age, signif icant past medical hist ory and t he nat ure of t he precipit at ing event . Sepsis has t he highest mort alit y and polyt rauma t he low est . Early deat hs are usually relat ed t o t he precipit at ing cause, w hereas lat e deat hs are associat ed w it h mult i-organ f ailure. Pneumot horax is common w it h high PAWP and damaged lung t issue. Once drained vent ilat ion may be diff icult because t he air leak reduces t he abilit y t o maint ain PEEP in t he ‘good’ lung, t hus reducing alveolar recruit ment result ing in w orsening hypoxaemia. SCC pp 91–96

106

M CQs

Key Quest ions in Surgical Crit ical Care

A 48. A. f alse

B. t rue

C. t rue

D. f alse

E. f alse

SCC p 95

A 49. A. t rue

B. t rue

C. f alse

D. t rue

E. f alse

Answ ers

In t ension pneumot horax air ent ers t he pleural space w it h vent ilat ion and is unable t o escape, usually due t o a t issue f ragment act ing as a one w ay valve at t he sit e of injury. The int rapleural pressure on t he aff ect ed side becomes posit ive and may increase t o over 40 mmHg. The increased int rapleural pressure ‘pushes’ t he mediast inum t ow ards t he side of t he healt hy lung so reducing eff ect ive vent ilat ion. The t rachea w ill be deviat ed aw ay f rom t he collapsed lung. Tension pneumot horax is a medical emergency and t he diagnosis is clinical. The risk of cardio-respirat ory compromise or arrest is signif icant , and act ion needs t o be immediat e. There should be no delay f or CXR.

Respiratory System

In open pneumot horax, caused by a penet rat ing injury, t he lung on t he aff ect ed side collapses and does not cont ribut e t o vent ilat ion. Vent ilat ion may be compromised in t he healt hy lung because of air exchange bet w een t he t w o lungs, mediast inal shif t t ow ards t he good lung and because of inadequat e expansion due t o t he w eight of t he aff ect ed collapsed lung. There is usually t achypnoea and respirat ory dist ress.

SCC p 53, p 95

A 50. A. t rue

B. f alse

C. f alse

D. f alse

E. t rue

⫹ CO2 is convert ed t o HCO⫺ 3 and H by carbonic anhydrase, and over 80% is carried in t his w ay. M ost of t he HCO⫺ 3 f ormed diff uses out of t he red blood cell (RBC) int o t he plasma. To maint ain elect rical neut ralit y Cl ⫺ ions diff use f rom t he plasma int o t he RBC (chloride shif t ). Carbamino compounds are mainly formed with haemoglobin, with less than a tenth being combined w it h plasma prot eins. A small amount of CO2 is t ransport ed dissolved in plasma despit e it s great er aff init y t han O2.

SCC pp 66–69

A 51. A. f alse

B. f alse

C. t rue

D. f alse

E. f alse

Haemoglobin is t he principle buff er of H⫹ liberat ed by t he t ransport of CO2. The binding (buff ering) capacit y of

M CQs

Key Quest ions in Surgical Crit ical Care

107

deoxyhaemoglobin is higher t han oxyhaemoglobin w hich is manif est by t he low er pH (i.e. more H⫹ ions t ransport ed) of venous blood. By buff ering t he liberat ed H⫹ ions f rom t he react ion:

Respiratory System

CO2 + H2O ⇌ HCO3− + H+

M ore CO2 can be t aken up in t he blood f or t ransport . This is t he Haldane eff ect . Chloride shif t ref ers t o int racellular (RBC) movement of Cl ⫺ t heref ore venous blood RBC have more Cl ⫺ t han art erial. SCC pp 66–69

A 52. A. f alse

B. f alse

C. t rue

D. t rue

E. f alse

Haemoglobin is a prot ein of 65,000 Dalt ons. Haem is a complex of porphyrin and Fe2⫹. As O2 combines w it h t he haem groups t he aff init y f or t he remaining groups increases, hence t he sigmoid shape of t he curve. The oxygen carrying capacit y of t he blood is det ermined by t he f ollow ing f ormula: Answ ers

O2 capacity = (Hb ×

Sat

100

× 1.34) + (PaO2 × 0.003)

1.34 is a const ant (t he number of millilit res carried by 1 g Hb). It can be seen t hat by f ar t he most signif icant f act or in oxygen carrying capacit y is t he Hb ⫻ sat . By increasing f ull sat urat ed Hb t he O2 cont ent is increased most signif icant ly. The dissolved port ion is relat ively minor and unimport ant . SCC pp 66–69

A 53. A. t rue

B. f alse

C. f alse

D. t rue

E. f alse

A lef t shif t increases t he slope of t he oxyhaemoglobin dissociat ion curve (ODC) because of t he increased aff init y of Hb f or O2. Conversely a right shif t decreases t he aff init y of Hb f or O2, and t he O2 is more easily released t o t he t issues. The Bohr eff ect ref ers t o t he shif t t o t he right of t he ODC caused by increased levels of CO2 in t he t issues. This allow s oxygen t o be liberat ed since t he aff init y of Hb f or O2 is reduced. The ODC is moved t o t he right by ↑ CO2 (Bohr eff ect ), ↑ t emp and ↑ 2,3-diphosphoglycerat e (2,3-DPG). 2,3-DPG binds avidly t o deoxyhaemoglobin.

108

M CQs

Key Quest ions in Surgical Crit ical Care

A 54. A. f alse

B. f alse

C. t rue

D. f alse

E. t rue

A 55. A. f alse

B. f alse

C. f alse

D. f alse

Respiratory System

M ixed venous sat urat ion corresponds t o P75 and is usually 5.3 kPa. P50 represent s t he level at w hich Hb is 50% loaded w it h O2 and is usually 3.46 kPa. P50 is used as an index of right or lef t shif t of t he ODC. Lef t shif t increases P50 and conversely right shif t decreases. Fet al Hb, myoglobin and CO dissociat ion curves all lie t o t he lef t of t he ODC. Fet al Hb has a higher aff init y f or O2 t han adult Hb and t heref ore ret ains O2 at low PaO2. M et haemoglobin has a f lat dissociat ion curve and is f ormed w hen f errous iron is oxidised t o f erric. M et haemoglobin has no aff init y f or O2.

E. t rue

Answ ers

Hyperoxia may develop because of increased inspired concent rat ion or increased t ot al pressure of O2, as occurs during diving. The crit ical level f or O2 t oxicit y is 40 kPa and t he risks increase as t he PIO2 increases, and w it h prolonged exposure. Lung damage occurs due t o decreased surf act ant product ion and result ant absorpt ion at elect asis and airw ay collapse. Init ial sympt oms are coughing and pain during breat hing, t his can lead t o convulsions and loss of consciousness. Inf ant s are more suscept ible t o oxygen t oxicit y and may be rendered blind if exposed t o PIO2 ⬎ 40 kPa due t o damage t o vit reous body. SCC pp 76–78

A 56. A. t rue

B. f alse

C. f alse

D. f alse

E. t rue

Surf ace t ension exist s in t he lungs at t he boundary of bet w een liquid and gas in t he alveoli. Laplace’s law st at es t hat t he w all t ension is direct ly proport ional t o t he product of t ransmural pressure and cylinder radius. Because of t his relat ionship alveoli of smaller diamet er experience higher surf ace t ension f orces and w ould t end t o empt y int o a larger alveolus. Surf act ant low ers surf ace t ension and is more eff ect ive in smaller alveoli. Surf act ant def iciency leads t o airw ay collapse. This may be seen in premat ure inf ant s w ho have reduced levels of surf act ant , leading t o respirat ory dist ress syndrome (RDS). SCC pp 59–60

M CQs

Key Quest ions in Surgical Crit ical Care

109

A 57. A. f alse

B. f alse

C. t rue

D. f alse

Dead space can be divided int o anat omical, corresponding t o t he conduct ing airw ays dow n t o t he t erminal bronchioles; and alveolar dead space. These t oget her f orm physiological dead space. Anat omical dead space is measured by Fow ler’s nit rogen w ashout met hod. Physiological dead space is measured using t he Bohr equat ion and is of t en f ract ionally larger t han anat omical dead space because it t akes account of under proposed alveoli. Anat omical dead space is usually of t he order of 2 ml/kg or 150 ml f or an average adult . Dead space account s f or about a t hird of t idal volume.

Respiratory System

SCC pp 59–60

Answ ers

110

E. f alse

M CQs

Key Quest ions in Surgical Crit ical Care

Other Systems and Multisystem Failure A 1.

A. f alse

B. t rue

C. f alse

Answ ers

D. f alse

E. t rue

Glasgow (& Ranson’s) crit eria are used f or indicat ion of a severe at t ack of pancreat it is. The def ined crit eria are: 䊏 䊏 䊏 䊏 䊏 䊏 䊏 䊏

Age ⬎ 55 years Whit e cell count (WCC) ⬎ 15 ⫻ 109/l Urea ⬎ 16 mmol/l Glucose ⬎ 10 mmol/l Calcium ⬍ 2 mmol/l Albumin ⬍ 32 g/l Art erial pO2 ⬍ 8kPa Lact at e dehydrogenase (LDH) ⬎ 600 iu/l SCC pp 131–135

Surgery 1999 17: 11; 261–265

A 2.

A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

The f ollow ing are f act ors inf luencing rebleeding: 䊏 䊏 䊏 䊏 䊏 䊏 䊏 䊏

Age ⬎ 60 Shock on admission Chronic rat her t han acut e ulcer Gast ric ulcer Underlying medical problem Bleeding source unknow n ⬎5 unit t ransf usion Bleeding f rom varices or malignancy SCC pp 129–131

Surgery 1999 17: 12; 293–298

A 3.

A. f alse

B. f alse

C. f alse

D. f alse

E. t rue

Organ f ailure in severe pancreat it is is usually respirat ory, cardiovascular, renal t hen disseminat ed int ravascular coagulat ion (DIC). Tw o organ syst em f ailure has a mort alit y of about 55% w hereas t hree or more is associat ed w it h a mort alit y of ⬎90% .

M CQs

Key Quest ions in Surgical Crit ical Care

111

Other Systems and Multisystem Failure

Hypercalcaemia and hypomagnesaemia are t he most common met abolic dist urbances and solid inf ect ed necrosis requires surgical debridement . Posit ive end expirat ory pressure (PEEP) may prevent t he development of adult respirat ory dist ress syndrome (ARDS). SCC pp 131–135

Surgery 1999 17: 11; 261–265

A 4.

A. t rue

B. f alse

C. f alse

D. t rue

E. f alse

Vesical dist ension is common, supravesical uncommon. A percutaneous nephrostomy should be performed to decompress a supravesical obstruction. For pelvic malignancy, double J stents should be used palliatively and nephrostomy tubes avoided. SCC pp 117–124

Surgery 1996 14: 12; 272–275

A 5.

A. t rue

B. f alse

C. t rue

D. f alse

E. f alse

Answ ers

M ost chest injuries can be managed by int ercost al t ube drainage, analgesia and appropriat e f luid management . M assive haemot horax is ⬎1500 ml blood and blood loss of ⬎200 ml is an indicat ion f or t horacot omy. SCC pp 146–151

Surgery 1996 14: 1; 9–12

A 6.

A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Transect ed aort a is a t ypical high velocit y decelerat ion injury. Bilat eral rib f ract ures occur in major crush injuries. SCC pp 146–151

Surgery 1996 14: 1; 9–12

A 7.

A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Hypovolaemia, decreased cardiac out put haemorrhage, cardiac t amponade, pulmonary cont usion, vent ilat ory f ailure and mediast inal disrupt ion can all cause hypoxia f ollow ing t horacic t rauma. SCC pp 146–151

Surgery 1996 14: 1; 9–12

A 8.

A. t rue

B. f alse

C. f alse

D. t rue

E. f alse SCC pp 117–122

112

M CQs

Key Quest ions in Surgical Crit ical Care

A. t rue

B. t rue

C. t rue

D. t rue

E. f alse

Ext radural haemat omas are associat ed w it h lucid int ervals rat her t han subdural haemat omas. SCC pp 99–107

A 10. A. t rue

B. f alse

C. f alse

D. f alse

E. t rue

Feat ures are: Hypovolaemic shock

Tachycardia and hypot ension

Neurogenic shock

Paralysis, bradycardia and hypot ension

Spinal shock

Flaccid muscles, absent ref lexes and loss of sensat ion SCC pp 108–112

A 11. A. t rue

B. f alse

C. f alse

D. t rue

E. f alse

Answ ers

High f low oxygen t herapy is necessary unt il carboxyhaemoglobin (COHb) levels are less t han 10% . Smoke only causes damage t o t he larynx and pharynx. Early int ubat ion should be perf ormed if t here are any doubt s as t o t he airw ay.

Other Systems and Multisystem Failure

A 9.

SCC pp 151–157

A 12. A. f alse

B. f alse

C. f alse

D. f alse

E. f alse

Gast roint est inal st ress ulcerat ion is common. Virt ually all crit ically ill pat ient s have endoscopic evidence of it . Signif icant bleeds occur in 10–20% . In only 1–2% of cases does prophylaxis have any eff ect on mort alit y and out come. H2 ant agonist s should be used f or high-risk pat ient s. Surgical int ervent ion is rarely necessary. SCC pp 129–131

A 13. A. t rue

B. f alse

C. f alse

D. t rue

E. t rue

Inf lammat ory bow el disease and dysphagia are indicat ions. Proximal small bow el f ist ulae, severe diarrhoea and small bow el obst ruct ion are cont ra-indicat ions as are ileus w it h dilat ed small int est ine and severe pancreat it is. SCC pp 140–146

M CQs

Key Quest ions in Surgical Crit ical Care

113

Other Systems and Multisystem Failure

A 14. A. t rue

B. f alse

C. f alse

D. t rue

E. t rue

Daily full blood count (FBC), urea and electrolytes (U & E), glucose and prothrombin time. Albumin is necessary t w ice w eekly and calcium w eekly. SCC pp 140–146

A 15. A. f alse

B. f alse

C. t rue

D. f alse

E. t rue

Rect al examinat ion in pat ient s w it h pelvic injury/f ract ure is mandat ory t o exclude open f ract ures or high riding prost at e. Cat het erisat ion should occur af t er uret hral injury has been excluded. Airw ay, Breat hing and Circulat ion (ABC) remains t he priorit y. SCC pp 146–151

A 16. A. f alse

B. f alse

C. t rue

D. t rue

E. t rue

Answ ers

Hypert hermia is def ined as a core t emperat ure above 40.5⬚C and is associat ed w it h respirat ory alkalosis. Dant rolene is used along w it h oxygen and t he cessat ion of t he anaest het ic t o t reat malignant hyperpyrexia. A 17. A. f alse

B. t rue

C. t rue

D. f alse

E. t rue

Leaks occur in 10–15% of colonic anast amoses. Dehydrat ed and shocked pat ient s have a higher incidence of leaks. Percut aneous CT (or ult rasound) guided drainage may be usef ul. A 18. A. f alse

B. f alse

C. t rue

D. f alse

E. t rue

Cef uroxime is a 2nd generat ion cephalosporin. Penicillin/cephalosporin cross-hypersensit ivit y has an incidence of approximat ely 5–10% . They are bot h eliminat ed via t he kidney. SCC p 174

A 19. A. t rue

B. f alse

C. t rue

D. t rue

E. f alse

The crit eria are: 䊏 䊏

114

M CQs

Haemodynamically st able af t er resuscit at ion No persist ent or increasing abdominal pain or t enderness

Key Quest ions in Surgical Crit ical Care

䊏

No ot her perit oneal injuries requiring laparot omy ⬍4 unit s blood t ransf usion required

Comput erised t omography f indings 䊏 䊏

Haemoperit oneum ⬍500 ml Simple hepat ic parenchymal lacerat ion or int ra-hepat ic haemat oma SCC pp 146–151

A 20. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Perit onit is, eviscerat ion and abdominal gunshot w ounds are all indicat ions f or laparot omy as are uncont rolled haemorrhage, persist ent shock and a clinical det eriorat ion. SCC pp 146–151

A 21. A. t rue

B. f alse

C. t rue

D. t rue

E. f alse

Other Systems and Multisystem Failure

䊏

The commonest f our complicat ions are: 䊏 䊏 䊏

Rebleeding (consider angiography and select ive embolisat ion) Bile leaks (ERCP plus endoscopic sphinct erot omy plus st ent ing) Ischaemic segment s Inf ect ed f luid collect ions

Answ ers

䊏

CT/ult rasound can allow ident if icat ion of collect ions and percut aneous drainage. Subhepat ic sepsis (1 in 5 cases) usually relat es t o bile leak, ischaemic t issue, undrained collect ions or bow el injury. A 22. A. f alse

B. f alse

C. f alse

D. t rue

E. t rue

M ort alit y af t er hepat ic injury 䊏 䊏 䊏 䊏 䊏

Overall 10–15% Penet rat ing (civilian) 1% Blunt ⬎ 20% Blunt (liver only) 10% Blunt (3 major organs injured) ⬎ 70%

Bleeding causes ⬎50% of deat hs. SCC pp 146–151

M CQs

Key Quest ions in Surgical Crit ical Care

115

Other Systems and Multisystem Failure

A 23. A. t rue

B. t rue

C. f alse

D. f alse

E. t rue

A high index of suspicion is necessary t o recognise pancreat ic t rauma. Abdominal X-ray (AXR) may show ret roperit oneal air or diaphragmat ic rupt ure. Serum amylase is a poor indicat or and can be normal in pat ient s w it h severe pancreat ic damage. Cont rast enhanced CT is t he best invest igat ion and demonst rat es pancreat ic oedema or sw elling and collect ions. ERCP should be used t o assess t he duct s. SCC pp 146–151

A 24. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Pancreat ic t rauma can lead t o pseudocyst , f ist ulae, ascit es int ra-abdominal abscess, w ound inf ect ion, pancreat ic abscess and acut e and chronic pancreat it is. SCC pp 146–151

A 25. A. t rue

B. f alse

C. t rue

D. t rue

E. t rue

Answ ers

Pat ient s are usually managed on ITU. Ent eral f eeding recommences as early as possible. Daily LFTs are perf ormed. St eroids are rapidly t ailed off . Immunosuppressive regimes most ly include cyclosporin or t acrolimus w it h azat hioprine, mycophenolat e mof et il and prednisolone. Acut e reject ion occurs in 50% but is t reat ed by ext ra st eroids or an alt ered drug regimen. Inf ect ion is a major cause of morbidit y. SCC pp 135–139

A 26. A. f alse

B. t rue

C. t rue

D. f alse

E. t rue

Hepat ocellular carcinoma has a low incidence of recurrence and as such a small t umour is not a cont ra-indicat ion. Inabilit y t o comply w it h drug t herapy is an addit ional cont ra-indicat ion. Neuroendocrine t umours and sarcomat a w it h liver met ast ases can do w ell w it h t ransplant at ion f or several years. SCC pp 135–139

A 27. A. t rue

B. t rue

C. t rue

D. f alse

E. f alse

The mort alit y if t w o ot her organ syst ems are involved is 95% . The elect rolyt e sequelae of acut e renal f ailure (ARF) are 116

M CQs

Key Quest ions in Surgical Crit ical Care

SCC pp 117–122

Surgery 2000 18: 6; 135–138

A 28. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Post operat ive hepat ic dysf unct ion may be due t o excess bilirubin (t ransf usion or haemolysis), hepat ocellular damage (pre-exist ing, viral hepat it is, sepsis, hypot ension, hypoxaemia or halot haneinduced hepat ic necrosis) or ext rahepat ic biliary obst ruct ion (gallst ones, ascending cholangit is, pancreat it is or surgical damage t o t he common bile duct ). SCC pp 135–139

Surgery 2000 18: 7; 180–181

A 29. A. t rue

B. f alse

C. t rue

D. t rue

E. f alse

SCC pp 112–116

A 30. A. t rue

B. f alse

C. f alse

D. t rue

Answ ers

Plat elet act ivat ing f act or (PAF), TNF-␣, Int erleukins 1, 6, 8, 2, 10 and monocyt e chemot act ic prot ein-1 are t he major inf lammat ory mediat ors in SIRS.

Other Systems and Multisystem Failure

hypocalcaemia, hyperkalaemia and met abolic acidosis. Uraemia can lead t o pericardit is, drow siness t remor and conf usion.

E. t rue

M ajor t rauma result s in increased prolact in, ant i-diuret ic hormone (ADH), cat echolamine and cort isol and decreased t hyroxine (T3 and T4). SCC pp 146–151

A 31. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Dose modif icat ion may be necessary w it h all ant ibiot ics in pat ient s w it h acut e renal f ailure. Close monit oring is necessary. SCC pp 117–122

A 32. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Acut e subdural injuries are associat ed w it h a lucid int erval in approximat ely 10–15% of cases. SCC pp 99–107

M CQs

Key Quest ions in Surgical Crit ical Care

117

Other Systems and Multisystem Failure

A 33. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue SCC pp 146–151

A 34. A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

Burns pat ient s require energy dense f eeds but do not t olerat e high volumes. 2000 ml f eeds provide 70 g prot ein t ypically. Glut amine is an essent ial amino acid. SCC pp 140–146

A 35. A. t rue

B. f alse

C. t rue

D. t rue

E. t rue

Complicat ions are:

Answ ers

M echanical

t ube blockage, aspirat ion, naso-pharyngeal irrit at ion, t ube misplacement

Inf ect ion

occurs more w it h parent eral nut rit ion

Physiological

diarrhoea, hypoalbuminaemia, nausea and vomit ing, hyperglycaemia, hypercapnia, f luid overload SCC pp 140–146

A 36. A. f alse

B. f alse

C. f alse

D. f alse

E. f alse

Haemot horax is t he commonest injury and 80% require not hing more t han an int ercost al chest drain. SCC pp 146–151

A 37. A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

Epidural haemat oma classically have a lucid int erval (alt hough subdural haemot oma (SDH) have one in about 15% ) and carry t he bet t er prognosis. Int ra-cranial pressure (ICP) in an adult should be less t han 15 mmHg. M anagement is geared at t he prevent ion of secondary brain injury and involves oxygenat ion and vent ilat ion and t he maint enance of cerebral perf usion pressure (CPP) ⬎60 mmHg. SCC pp 99–107

118

M CQs

Key Quest ions in Surgical Crit ical Care

B. f alse

C. t rue

D. t rue

E. t rue

ICP requires t reat ment at levels ⬎15 mmHg. Sedat ion decreases cerebral blood f low. Aggressive hypervent ilat ion can increase ICP. SCC pp 99–107

A 39. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

M onit oring of pressure areas should also be perf ormed. SCC pp 108–112

A 40. A. t rue

B. t rue

C. f alse

D. f alse

E. t rue

Pulmonary sepsis is t he leading cause of deat h. The hypermet abolic response peaks at 7–10 days. SCC pp 151–157

B. t rue

C. t rue

D. t rue

E. t rue

Respirat ory insuff iciency f orms part of a f ailure t o respond t o ICU t herapy.

Answ ers

A 41. A. f alse

Other Systems and Multisystem Failure

A 38. A. t rue

SCC pp 131–135

A 42. A. t rue

B. t rue

C. f alse

D. f alse

E. f alse

Fract ional excret ion Na ⬍ 1% ; urine Cr/plasma Cr ⬎ 40 are suggest ive of pre-renal renal f ailure. Other features include urinary blood urea nitrogen (BUN)/plasma BUN ⬎ 8; plasma BUN/Cr ⬎ 20, urine sodium ⬍ 20 mmol/L and urine osmolalit y ⬎ 500 mosm/kg H2O. SCC pp 117–122

A 43. A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

95% of pot assium is int racellular. Hart mann’s solut ion should be avoided in renal f ailure as it cont ains pot assium and can lead t o hyperkalaemia. The st ress response t o surgery also result s in w at er ret ent ion. SCC p 140

M CQs

Key Quest ions in Surgical Crit ical Care

119

Other Systems and Multisystem Failure

A 44. A. f alse

B. f alse

C. t rue

D. f alse

E. f alse

Fat embolism most commonly occurs af t er long bone f ract ure. Reaming and t he insert ion of int ramedullary nails also increase risk. Heparinisat ion is not only unnecessary but may lead t o compart ment syndrome. High dependency/int ensive care monit oring is essent ial and vent ilat ion may be necessary. Development of f at embolism syndrome (FES) occurs in approximat ely 5% . Fat embolism is rare in pancreat it is. SCC pp 158–160

A 45. A. t rue

B. f alse

C. f alse

D. t rue

E. t rue

Sympt oms and signs of FES: 䊏 䊏

Answ ers

䊏

Respirat ory – dyspnoea, t achypnoea, hypoxaemia, ARDS, inf ilt rat es on CXR CNS – anxiet y, irrit at ion, conf usion, convulsions, cerebral oedema on CT Other – petechial rash, retinal haemorrhages, tachycardia, fever SCC pp 158–160

A 46. A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Blood loss is mediat ed by hypovolaemic shock. SCC pp 146–151

A 47. A. t rue

B. f alse

C. t rue

D. f alse

E. f alse SCC pp 135–139

A 48. A. t rue

B. t rue

C. t rue

D. t rue

E. f alse

Age has no eff ect on t he risk of developing ATN. SCC pp 117–122

A 49. A. t rue

B. f alse

C. t rue

D. t rue

E. f alse

Benzyl penicillin may cause nephrit is. SCC pp 117–122

120

M CQs

Key Quest ions in Surgical Crit ical Care

B. t rue

C. t rue

D. t rue

E. t rue

Table 3.1 Crit eria f or t ransf er t o a burns cent re Second- and t hird-degree burns ⬎10% TBSA in pat ient s ⬍10 or ⬎50 years of age Second- and t hird-degree burns t o ⬎20% TBSA in all ot her ages Third-degree burns ⬎5% TBSA in pat ient s of any age All second- and t hird-degree burns w it h t he t hreat of f unct ional or cosmet ic impairment t o t he f ace, hands, f eet , genit alia, perineum or major joint s All elect rical burns, including light ning injuries Chemical burns Burns involving inhalat ion injury Circumf erent ial burns of t he ext remit ies and/or chest Burns involving concomit ant t rauma among w hich t he burn injury poses t he great est risk of morbidit y or mort alit y. Burns in pat ient s w it h pre-exist ing medical condit ions t hat may complicat e management and/or prolong recovery, such as coronary art ery disease, lung disease or diabet es.

A 51. A. f alse

B. t rue

C. t rue

D. t rue

E. f alse

Answ ers

SCC pp 151–157

Other Systems and Multisystem Failure

A 50. A. t rue

M et abolic acidosis may be classif ied int o t hose w it h a normal or high anion gap. The normal cat ions present in plasma are Na, K, Ca, M g. The normal anions are Cl, HCO3, and negat ive charges present on albumin, phosphat e, sulphat e, lact at e, and ot her organic acids. The sum of negat ive and posit ive charges must be equal. The readily measured cat ions and anions give t he anion gap according t o t he equat ion: Anion gap ⫽ {[Na] ⫹ [K]} ⫺ {[Cl] ⫹ [HCO3]}

Because t here are more unmeasured anions t han cat ions, t he normal anion gap is 10–18 mmol/l. Lact ic acidosis is charact erised by a high anion gap because t he unmeasured lact at e anion is present in increased quant it ies. Increased lact ic acid product ion occurs w hen cellular respirat ion is abnormal (t ype A) or due t o a met abolic abnormalit y (t ype B). The commonest cause of lact ic acidosis is poor t issue perf usion due t o cardiogenic shock, post cardiac arrest , or sepsis (t ype A).

M CQs

Key Quest ions in Surgical Crit ical Care

121

Other Systems and Multisystem Failure

Type B lact ic acidosis may be caused by liver f ailure or met f ormin accumulat ion, t ypically in renal f ailure. The management of lact ic acidosis should address t he underlying cause and aims t o opt imise t issue perf usion and oxygen delivery t hrough volume replacement , vent ilat ory and inot ropic support . The administ rat ion of sodium bicarbonat e may t heoret ically w orsen int racellular acidosis t hrough increased generat ion of CO2 and should be limit ed t o severe acidosis (e.g. pH ⬍ 7.1).

A 52. A. f alse

B. t rue

C. t rue

D. f alse

E. t rue

Answ ers

DIC is charact erised by act ivat ion of t he clot t ing cascades w it h generat ion of f ibrin, consumpt ion of clot t ing f act ors and plat elet s, and secondary act ivat ion of f ibrinolysis leading t o product ion of f ibrinogen degradat ion product s (FDPs). DIC may be asympt omat ic manif est only on blood invest igat ions, or may result in bleeding, or t issue ischaemia due t o vessel occlusion by f ibrin and plat elet s. The prot hrombin t ime (or int ernat ional normalised rat io (INR)), act ivat ed part ial t hromboplast in t ime (APTT), and t hrombin t ime are usually prolonged. The f ibrinogen level and plat elet count are low. High levels of FDPs are present . There may be f ragment ed red cells on t he blood f ilm due t o red cell damage during passage t hrough f ibrin w ebs in t he circulat ion. Treat ment is aimed at correct ing t he underlying cause. Blood product support (plat elet s, f resh f rozen plasma (FFP), cryoprecipit at e, packed red cells) is given under haemat ology advice. SCC pp 47–49

A 53. A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

DIC may be caused by gram-negat ive, meningococcal and st aphylococcal sept icaemia, t issue damage af t er t rauma, burns or surgery, malignancy, haemolyt ic blood t ransf usion react ions, f alciparum malaria, snake bit es, and obst et ric condit ions such as placent al abrupt ion and amniot ic f luid embolism. SCC pp 47–49

122

M CQs

Key Quest ions in Surgical Crit ical Care

B. f alse

C. t rue

D. t rue

E. t rue

These art erial blood gases demonst rat e an acidosis (t he pH is ⬍7.36). Respirat ory acidosis is caused by ret ent ion of CO2, most commonly due t o chronic obst ruct ive pulmonary disease (COPD), so t his case cannot be respirat ory in origin because t he pCO2 is low. The primary abnormalit y must be t he low bicarbonat e eit her due t o increased bicarbonat e loss, or more commonly due t o it s consumpt ion t o buff er increased acid product ion or reduced acid excret ion. This is t heref ore a met abolic acidosis, and t he pCO2 is low as t he pat ient hypervent ilat es t o blow off CO2. This is called respirat ory compensat ion f or met abolic acidosis. Respirat ory f ailure is not present because t here is neit her hypoxia or hypercapnoea. M et abolic acidosis may be caused by: 䊏 䊏 䊏 䊏 䊏

Answ ers

䊏

Failure t o excret e acid, e.g. renal f ailure, t ype I (dist al) and t ype IV renal t ubular acidosis Ingest ion of acid, e.g. salicylat e poisoning Excess product ion of acid, e.g. diabet ic ket oacidosis Anaerobic product ion of lact ic acid Increased product ion of hydrochloric acid (high prot ein int ake) Increased bicarbonat e loss, e.g. gast roint est inal f rom diarrhoea, ileost omy, uret erosigmoidoscopy, or renal in t ype II (proximal) renal t ubular acidosis

Other Systems and Multisystem Failure

A 54. A. f alse

SCC pp 112–122

A 55. A. f alse

B. f alse

C. t rue

D. t rue

E. t rue

These art erial blood gases demonst rat e t ype II respirat ory f ailure. Respirat ory f ailure is classif ied int o t ype I, in w hich pCO2 is normal or low, and t ype II in w hich pCO2 is elevat ed, as in t his case. Causes of t ype I respirat ory f ailure include COPD, pulmonary oedema, pneumonia, ARDS, pulmonary embolism and f ibrosing alveolit is. Type II respirat ory f ailure may be caused by COPD, depression of t he respirat ory cent re (e.g. opiat es, benzodiazepines), respirat ory muscle w eakness, and chest w all def ormit ies. There is also a respirat ory acidosis: t he pH is low indicat ing acidosis, and t he pCO2 is raised indicat ing t hat CO2 ret ent ion

M CQs

Key Quest ions in Surgical Crit ical Care

123

Other Systems and Multisystem Failure

is t he cause of t he acidosis. In chronic respirat ory acidosis (most commonly caused by COPD), renal ret ent ion of bicarbonat e is increased. This is know n as met abolic compensat ion. In t his case, t he bicarbonat e concent rat ion is normal, suggest ing t hat t he respirat ory acidosis is acut e. Severe acut e ast hma init ially result s in hypervent ilat ion w it h a low pCO2. In a lif e-t hreat ening at t ack, t he pCO2 may rise as t he pat ient t ires. This is a grave sign and is an indicat ion f or mechanical vent ilat ion. SCC pp 79–80

A 56. A. t rue

B. t rue

C. f alse

D. f alse

E. f alse

Answ ers

Syst emic inf lammat ory response syndrome (SIRS) is a prot ect ive inf lammat ory response t o an insult or invading pat hogen. Tissue injury act s as a precipit ant and t he common causes are inf ect ion, t rauma, t umour invasion, hypoxia and ischaemia. Burns pat ient s are part icularly suscept ible t o SIRS w hich is a considerable cause of morbidit y. The immune react ion is not abnormal but paradoxically leads t o f urt her t issue damage because of hypovolaemia and result ant poor t issue perf usion. Alt hough mult i-organ dysf unct ion syndrome (M ODS) is a consequence of SIRS, t he progression is not aut omat ic and can be avoided by clinical int ervent ion. SCC pp 112–116

A 57. A. f alse

B. t rue

C. t rue

D. t rue

E. t rue

The diagnosis of SIRS is made by t he pat ient f ulf illing t w o or more of t he f ollow ing crit eria: I. II. III. IV.

Core t emperat ure ⬎ 38 or ⬍36⬚C Heart rat e ⬎ 90 beat s per minut e Respirat ory rat e ⬎ 20 breat hs per minut e or PaCO2 ⬍ 4.26 kPa WCC ⬎ 12 ⫻ 109/l or ⬍4 ⫻ 109 (w it h ⬎10% neut rophils or immat ure f orms) SCC pp 112–116

A 58. A. t rue

B. f alse

C. f alse

D. f alse

E. t rue

Typically t he pat ient w ill have w arm, f lushed peripheries, w it h diast olic hypot ension and t achycardia. Nit ric oxide exert s a 124

M CQs

Key Quest ions in Surgical Crit ical Care

SCC pp 112–116

A 59. A. f alse

B. f alse

C. t rue

D. f alse

E. t rue

Answ ers

M ODS is a progression f rom SIRS diagnosed by dysf unct ion of t w o or more organ syst ems. The inf lammat ory process of SIRS result s in hypoperf usion and t issue ischaemia. There is int erst it ial oedema f rom ext ravasat ion of f luid f rom damaged vascular endot helium. Oliguria occurs due t o hypovolaemia and hypoperf usion and occurs relat ively early, of t en during SIRS. If t reat ed prompt ly t his can be reversible and not a sign of end organ damage. As hypoperf usion cont inues, renal dysf unct ion becomes more diff icult t o reverse and t reat . Wit h prompt t reat ment w it h f luid resuscit at ion and ot her support ive measures progression t o irreversible mult i-organ f ailure syndrome (M OFS) can be avoided.

Other Systems and Multisystem Failure

relaxant eff ect on t he vasculat ure, opposing t he myogenic cont ract ion of t he vessel w alls. M et abolic acidosis may occur as a result of t issue hypoperf usion and lact ic acid f ormat ion. The pat ient may have deranged clot t ing f unct ion, because of act ivat ion of t he coagulat ion cascade, w it h t he clot t ing f act ors being consumed in t he react ion. This is also ref erred t o as consumpt ive coagulopat hy.

SCC pp 112–116

A 60. A. f alse

B. f alse

C. f alse

D. f alse

E. f alse

Fluid t herapy is essent ial t o count eract t issue hypoperf usion f rom hypovolaemia. Caref ul monit oring is required how ever, since t here is a risk of w orsening t issue oedema. Wit h acut e lung injury, t he risk of w orsening respirat ory f unct ion is increased w it h inappropriat e use of large volumes of f luids. Fluid resuscit at ion is key t o prevent ion of det eriorat ing organ f unct ion but must be balanced w it h appropriat e use of inot ropes. Inot ropes w hich increase af t erload (␣ agonist s) are of t en required but can cause myocardial dysf unct ion. ␤ agonist s are used t o t reat myocardial dysf unct ion and t o maint ain t issue perf usion. M easurement of cardiac out put is desirable but not mandat ory since invasive met hods do carry a risk of morbidit y, part icularly if t here is coagulopat hy. Art erial monit oring is not cont ra-indicat ed since

M CQs

Key Quest ions in Surgical Crit ical Care

125

Other Systems and Multisystem Failure

t he risk of dist al ischaemia is small and it provides essent ial inf ormat ion f or prescribing inot ropes. SCC pp 112–116

A 61. A. f alse

B. t rue

C. f alse

D. t rue

E. f alse

The mort alit y rat e depends on t he number of organ syst ems aff ect ed and t he durat ion of f ailure: Number of f ailed organ syst ems 2 3

M ort alit y rat e on day 1

M ort alit y rat e on day 4

50% 80%

65% 95%

M ort alit y is higher at ext remes of age, w it h t he presence of sepsis, burns and immunocompromise. The pre-morbid healt h of t he pat ient is also import ant in out come. SCC pp 112–116

Answ ers

A 62. A. t rue

B. t rue

C. f alse

D. f alse

E. t rue

Int racellular K+ is usually 155 mmol/l, and is t he most concent rat ed int racellular ion. Sodium is t he most abundant ext racellular ion. The daily Ca2+ requirement is 0.17 mmol/kg/day. M g 2+ is mainly int racellular w it h a concent rat ion of 2 mmol/l. SCC p 140

A 63. A. f alse

B. f alse

C. t rue

D. t rue

E. f alse

5% dext rose has an osmolalit y of 278 mosmol/kg w hich is less t han t hat of blood at 290 mosmol/kg. Hart mann’s solut ion has a Na+ concent rat ion of 131 mmol/l and Cl ⫺ concent rat ion of 111 mmol/l. Bot h N/saline and Hart mann’s solut ion are slight ly hypert onic compared t o blood, and are dist ribut ed in t he ECF. D/saline is dist ribut ed equally bet w een ICF and ECF. 5% dext rose is dist ribut ed t hroughout t ot al body w at er. SCC p 140

A 64. A. t rue

B. f alse

C. f alse

D. t rue

E. t rue

As a general rule replace like w it h like. Perit onit is result s in a loss of prot ein rich exudat e and pot ent ially large f luid shif t s. 126

M CQs

Key Quest ions in Surgical Crit ical Care

SCC p 140

A 65. A. f alse

B. f alse

C. t rue

D. f alse

E. t rue

Body mass index is w eight /height 2 䊏 䊏 䊏

Normal value is 20–25 25–30 is over w eight 30–35 is obese ⬎35 is morbidly obese

Answ ers

䊏

Other Systems and Multisystem Failure

Replacement should be w it h a f luid w it h high colloid osmot ic pressure. Albumin or art if icial colloids could also be used. Loss of ECF volume by vomit ing or diarrhoea should be replaced by N/saline or Hart mann’s solut ion. Diabet es mellit us t ends t o lose ECF by polyuria, Hart mann’s solut ion cont ains lact at e, so increasing t he risk of lact at ic acidosis. N/saline should be used. Diabet es insipidus loses t ot al body w at er and should be replaced by w at er (or 5% dext rose). Care should be t aken w it h 5% dext rose how ever if t here is a co-exist ing head injury since cerebral oedema may be precipit at ed. Burns may cause bleeding f rom t he init ial insult or af t er t heat re debridement . Any colloid may be used but if blood is lost it should be replaced.

Energy requirement s are 20–30 kcal/kg/day, usually 2000 kcal f or f emales, 2500 kcal f or males. Nit rogen requirement f or f emales is 7.5 g/day. In non-cat abolic pat ient s 1 g N should be given f or every 200 kcal energy. SCC pp 140–146

A 66. A. t rue

B. f alse

C. f alse

D. f alse

E. f alse

Nut rit ion should be modif ied in organ f ailure 䊏 䊏

䊏

M CQs

Respirat ory — high f at , low carbohydrat e (t o limit CO 2 product ion) Renal — low nit rogen (t o reduce urea product ion) — low f at (poor handling) — low sodium and w at er (t o reduce f luid overload) — low pot assium Cardiac — low sodium and w at er (t o reduce f luid overload)

Key Quest ions in Surgical Crit ical Care

127

Other Systems and Multisystem Failure

䊏

䊏

Liver — low sodium and w at er — low nit rogen (in encephalopat hic pat ient s) — adequat e carbohydrat e load (since t hey t end t ow ards hypoglycaemia) Cerebral — close blood glucose cont rol required — glucose is t he main subst rat e and hypoglycaemia should be avoided — hyperglycaemia w ill w orsen cerebral oedema SCC pp 140–146

A 67. A. f alse

B. f alse

C. t rue

D. f alse

E. f alse

Ent eral f eeding has a number of advant ages over t he parent eral rout e: 䊏

Answ ers

䊏 䊏

Ent eral f eeding is more physiological and allow s subst rat es t o be absorbed more gradually int o t he bloodst ream Gast ric prot ect ion unnecessary since t he f eed lines t he st omach (prot ect s against st ress ulcerat ion) M aint ains f unct ion of t he gut and prevent s at rophy reducing t he risk of t ranslocat ion of gut bact eria

Parent eral nut rit ion should only be used if ent eral nut rit ion is not possible. There is no advant age t o short t erm (days) use of parent eral nut rit ion. It w ill of t en lead t o hyperglycaemia and increases insulin requirement s. Bow el sounds are not oriously poor at predict ing t he f unct ion of t he gut . Absence of bow el sounds does not mean t hat ent eral nut rit ion should not be at t empt ed. SCC pp 140–146

A 68. A. t rue

B. t rue

C. t rue

D. f alse

E. f alse

Fat s and carbohydrat es are broken dow n t o CO2 and w at er, but prot eins are only broken dow n as f ar as urea. Fat gives t w ice as much energy per gram t han carbohydrat e or prot ein. About 65% of t he calories required per day comes f rom carbohydrat e, 25% f rom f at and 15% f rom prot ein. A high prot ein diet increases t he basal met abolic rat e (BM R) since more energy is required 128

M CQs

Key Quest ions in Surgical Crit ical Care

Respirat ory quot ient (RQ) =

 VCO rat e of CO2 f ormat ion 2 =  VO2 rat e of O 2 upt ake

RQ varies w it h diet , w it h carbohydrat e t he RQ is 1.0, f or f at s t he RQ is 0.7. Since t he proport ion of prot ein in t he diet varies relat ively lit t le t he overall RQ w ill vary bet w een 0.7 (f at t y diet ) and 1.0 (carbohydrat e diet ). SCC pp 140–146

Other Systems and Multisystem Failure

t o produce 1mol ATP f rom prot ein t han carbohydrat e (about 20% )

Answ ers

M CQs

Key Quest ions in Surgical Crit ical Care

129

Problems in Intensive Care A 1.

A. f alse

B. f alse

C. f alse

D. t rue

Answ ers

E. t rue

Diagnosis of brainst em deat h (BSD) in t he UK. Precondit ions: 䊏 䊏 䊏

Diagnosis compat ible w it h BSD Presence of irreversible st ruct ural brain damage Presence of apnoeic coma

Exclusions: 䊏

Drugs, Hypot hermia, M et abolic abnormalit ies, Int oxicat ion

Clinical Test s: 䊏

䊏

Absent brain st em ref lexes — No pupil response t o light — No corneal ref lex — No gag ref lex — No cough ref lex — No vest ibulo-ocular ref lex (50 ml ice-cold w at er) Persist ant apnoea SCC pp 183–185

Surgery 1999 17: 9; 205–207

A 2.

A. t rue

B. f alse

C. t rue

D. f alse

E. f alse

Deep inf ect ions w it h implant s can occur more t han a year af t er surgery. Operat ive w ound inf ect ion rat es: 䊏 䊏 䊏

Clean 0.8% Clean-cont aminat ed 1.3% Cont aminat ed 10.2%

Lat ex and silast ic drains increase t he rat e of inf ect ion f ollow ing abdominal surgery. 130

M CQs

Key Quest ions in Surgical Crit ical Care

Wounds should be shaved (or pref erably clipped) immediat ely prior t o surgery.

A 3.

A. f alse

B. f alse

C. f alse

D. t rue

E. f alse

Fat embolism syndrome (FES) occurs in approximat ely 5% of cases. FES is rarely seen w it h pancreat it is but does occur. Crush injuries cause f at embolism more t han open injuries. Fat embolism result s in hypoxaemia and hypocarbia on ABG analysis. SCC pp 158–160

A 4.

A. t rue

B. f alse

C. f alse

D. t rue

E. t rue

SCC pp 158–160

A 5.

A. t rue Age

A 6.

B. t rue

C. f alse

D. f alse

E. f alse

Heart rat e (HR)

Blood pressure (syst olic)

Respirat ory rat e (RR)

⬍1 year

120–140

70–90

30–40

2–5 years

100–120

80–90

20–30

5–12 years

80–120

90–110

15–20

A. f alse

B. f alse

C. t rue

D. t rue

Answ ers

Respirat ory signs of FES are dyspnoea, t achypnoea, hypoxaemia, bilat eral inf ilt rat es on CXR and ARDS. CNS signs include anxiet y, irrit at ion, conf usion, convulsions and cerebral oedema on CT. Ot her signs are a pet echial rash, ret inal haemorrhages, t achycardia and f ever. Laborat ory t est s include sudden anaemia and t hrombocyt openia and a raised ESR.

Problems in Intensive Care

SCC pp 175–179

Surgery 1999 17: 6; 126–130

E. f alse

Tw o set s of t est s perf ormed by t w o pract it ioners regist ered f or more t han 5 years, one of w hom is a consult ant , and neit her of w hom members of t he t ransplant t eam are required. Test s: 䊏 䊏

M CQs

Pupils f ixed and dilat ed No corneal ref lex

Key Quest ions in Surgical Crit ical Care

131

䊏 䊏 䊏

Problems in Intensive Care

䊏

No No No No

vest ibulo-ocular ref lexes CNS mot or responses gag ref lex respirat ory eff ort SCC pp 183–185

A 7.

A. t rue

B. t rue

C. t rue

D. f alse

E. f alse

Diabet es is a risk f or oropharyngeal colonisat ion but not nosocomial pneumonia. SCC pp 165–166, pp 175–177

A 8.

A. t rue

B. t rue

C. f alse

D. f alse

E. f alse

Head injury – St aphylococcus aureus Vent ilat ion – Pseudomonas Thoracoabdominal surgery – anaerobes Tracheot omy – Pseudomonas

Answ ers

SCC pp 175–177

A 9.

A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

As alw ays – cult ure and seek microbiological advice – and appropriat e ‘best guess’ ant ibiot ics. The suggest ed ant ibiot ics may not be t he best , but t hey are appropriat e. SCC pp 175–177

132

M CQs

Key Quest ions in Surgical Crit ical Care

Principles of Intensive Care A 1.

A. t rue

B. f alse

C. f alse

D. f alse

Answ ers

E. t rue

The acut e physiology and chronic healt h evaluat ion (APACHE) score is t he most commonly used scoring syst em in int ensive t herapy unit (ITU). SCC pp 198–201

A 2.

A. t rue

B. t rue

C. f alse

D. f alse

E. f alse

Diamorphine is met abolised by est er hydrolysis in t he liver, plasma and cent ral nervous syst em (CNS). It s half lif e is 5 minut es and it is less of a respirat ory depressant t han morphine. It may be given saf ely int rat hecally. SCC pp 203–205

A 3.

A. f alse

B. t rue

C. t rue

D. f alse

E. t rue

Epidural opioids are 10 t imes more pot ent t han int ravenous. Epidural haemat oma may lead t o cord compression and urinary ret ent ion occurs in 30% . SCC pp 203–205

Surgery 2000 18: 8; 198–201

A 4.

A. t rue

B. f alse

C. t rue

D. t rue

E. t rue

See early w arning t able in Viva Answ ers, p 226. SCC pp 189–191

A 5.

A. t rue

B. t rue

C. t rue

D. t rue

E. t rue

Early diagnosis and prompt t reat ment improves out come, increased age, illness severit y and decreased physiological reserve are all det riment al. SCC pp 198–201

M CQs

Key Quest ions in Surgical Crit ical Care

133

A 6.

A. f alse

B. t rue

C. f alse

D. t rue

E. t rue

Principles of Intensive Care

Alf ent anil is not sedat ive. Fent anyl unlike morphine does not cause hist amine release. SCC pp 203–205

A 7.

A. t rue

B. f alse

C. f alse

D. f alse

E. t rue

M edian nerve neuropat hy can arise f rom a haemat oma f ollow ing a brachial art ery cat het er. Up t o 50% of radial art ery cat het ers are associat ed w it h Doppler proven int ra-art erial t hromboses. A maximum rat e of 6% f or pneumot horaces af t er cent ral line insert ion has been demonst rat ed. Thoracic duct injury usually resolves w it h compression. SCC pp 205–207

A 8.

A. f alse

B. f alse

C. f alse

D. t rue

E. t rue

Answ ers

The aim of scoring syst ems used clinically is t o evaluat e out come f or diff erent groups of int ensive care unit (ICU) pat ient s. Scoring syst ems, do not predict out come or guide t reat ment planning f or individual pat ient s. They may be used t o det ermine pat ient groups according t o severit y of illness, at t ach risk t o diff erent groups or compare pat ient groups in ICU’s f rom diff erent hospit als. Risk adjust ment t akes int o account t he diff erences bet w een pat ient s t hat aff ect s t heir risk of a part icular out come e.g. age, premorbid illness, severit y of illness or emergency surgery. These f act ors const it ut e t he case-mix, case-mix adjust ment is t he process of account ing f or t hese in t he comparison of any out come measure. SCC pp 198–201

A 9.

A. f alse

B. f alse

C. f alse

D. t rue

E. t rue

The revised t rauma score (RTS) correlat es w ell w it h survival so t hat a high score is bet t er. RTS12 is associat ed w it h 99.5% survival and RTS0 3.7% survival. The scores range f rom 0 t o 12 by a combinat ion of Glasgow coma score (GCS), syst olic blood pressure and respirat ory rat e (RR). SCC pp 198–201

134

M CQs

Key Quest ions in Surgical Crit ical Care

A 10. A. f alse

B. f alse

C. t rue

D. t rue

E. f alse

SCC pp 198–201

A 11. A. f alse

B. f alse

C. t rue

D. f alse

E. t rue

The abbreviat ed injury score (AIS) is calculat ed by t he sum of t he squares of t he t hree highest cat egories f rom t he injury severit y scale (ISS). From AIS t he let hal dose in 50% (LD 50) has been calculat ed.

SCC pp 198–201

A 12. A. f alse

B. t rue

C. t rue

D. f alse

Answ ers

This is age dependent and is 40 f or 15–44 years, 29 f or 45–64 years and 20 f or t hose ⬎65 years. In ISS t here are seven anat omical areas and loss of consciousness (LOC) f or 12 minut es scores 2.

Principles of Intensive Care

APACHE st ands f or acut e physiology and chronic healt h evaluat ion. None of t hese scoring syst ems provides any predict ive pow er over individual t reat ment progression or out come. They are designed t o st rat if y pat ient s int o groups depending on t he acut e physiological insult and t ake int o account some aspect of signif icant chronic medical problems.

E. f alse

Thiopent one is a barbit urat e compound w hich is met abolised in t he liver. Thiopent one t ends t o accumulat e w it h repeat ed doses and t heref ore is not suit able f or prolonged use in general ICU pat ient s. It is occasionally used by inf usion on neuro ICU’s t o reduce t he met abolic demand f or oxygen of t he damaged brain. Prolonged inf usion requires elect roencephalogram (EEG) monit oring. Propof ol is an emulsion in soya f at and t heref ore has a high lipid cont ent . Ket amine is not a convent ional induct ion agent f or anaest hesia because it does not have a clearly def ined sleep point . It t ends t o be used as an analgesic and anaest het ic in f ield condit ions e.g. milit ary campaign. M idazolam is of t en used in long t erm inf usion but it is met abolised in t he liver t o act ive drugs w hich have sedat ive propert ies. Drugs used in ICU f or inf usions should be st opped periodically in order t o assess t heir eff ect on consciousness, t o avoid prolonged coma. SCC pp 203–205

M CQs

Key Quest ions in Surgical Crit ical Care

135

A 13. A. t rue

B. f alse

C. t rue

D. t rue

E. f alse

Principles of Intensive Care

M idazolam is a w at er soluble benzodiazepine w hich is used f or sedat ion as inf usion and bolus. It has a relat ively short durat ion of act ion as a bolus but cumulat es readily w hen given by inf usion leading t o prolonged coma. To prevent t his pat ient s should be assessed f requent ly and t heir sedat ion adjust ed. M idazolam is popular by inf usion because it is cheap, w at er soluble, can be given in relat ively concent rat ed inf usions and is reasonably f amiliar t o use. One arm-brain circulat ion t ime is about 30 seconds and sedat ives used f or rapid sequence induct ion should have t heir eff ect s w it hin t his. SCC pp 203–205

A 14. A. t rue

B. t rue

C. t rue

D. f alse

E. f alse

Answ ers

Despit e t heir similar eliminat ion half lives of about 4 hours, morphine is longer act ing because of t he rapid redist ribut ion of t he more lipid soluble f ent anyl. Alf ent anil has t he short est durat ion of act ion of t he commonly used sedat ives on ICU. Fent anyl and Alf ent anil inf usions can cont inue f or prolonged periods w it hout precipit at ing prolonged coma. M orphine has t w o act ive met abolit es w hich can cause prolonged sedat ion and apnoea. M orphine causes hist amine release and should be used w it h care in ast hmat ic pat ient s. SCC pp 203–205

A 15. A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

All opioids have t he t endency t o cause chest w all rigidit y t o some degree. Fent anyl and t he new ult ra-short act ing opioid remif ent anil seem t o be more responsible t han t he ot hers. All opioid eff ect s are reversed by naloxone including respirat ory depression, euphoria and nausea. M orphine 3 and 6 sulphat e are bot h act ive met abolit es and t end t o accumulat e w it h prolonged inf usions. This is part icularly t rue in pat ient s w it h hepat ic or renal f ailure w here f ent anyl or alf ent anil w ould be a more sensible choice. All opioids cause some degree of vasodilat at ion by a cent ral act ion, t he amount of accompanying hypot ension depends on t he individual drug. M orphine t ends t o cause more hypot ension t han alf ent anil or f ent anyl. SCC pp 203–205

136

M CQs

Key Quest ions in Surgical Crit ical Care

A 16. A. t rue

B. f alse

C. f alse

D. f alse

E. t rue

SCC pp 203–205

A 17. A. t rue

B. f alse

C. f alse

D. t rue

E. f alse

Answ ers

Suxamet honium is a depolarising muscle relaxant w hich ‘act ivat es’ t he neuromuscular junct ion causing visible f aciculat ion bef ore t emporarily paralysing it . It causes depolarisat ion because suxamet honium is st ruct urally relat ed t o t w o acet yl choline molecules joined t oget her, t hereby act ivat ing t he recept or. Suxamet honium is met abolised by plasma cholinest erase, an enzyme produced by t he liver w hich act s locally. Suxamet honium has a number of side-eff ect s including myalgia in young adult s, hyperkalaemia in burns and spinal injury pat ient s and raised int ra-opt ic and int ra-cranial pressure (t hese lat t er t w o are t emporary). Suxamet honium has rapid onset and off set and is primarily used f or rapid sequence int ubat ion.

Principles of Intensive Care

Rocuronium w orks w it hin 60 seconds and can be used as an alt ernat ive t o suxamet honium f or rapid sequence int ubat ion. At racurium is an est er w hich is kept ref rigerat ed because it undergoes spont aneous breakdow n at room t emperat ure, called Hoff mann degradat ion w hich is enzyme independent . At racurium is t he drug of choice f or ICU inf usions and in renal f ailure since it does not accumulat e. Vecuronium is a st eroid w hich is met abolised in t he liver and should be avoided in hepat ic f ailure because of t he risk of accumulat ion and prolonged paralysis. Vecuronium has an onset of 2–3 minut es.

SCC pp 203–205

A 18. A. f alse

B. f alse

C. t rue

D. f alse

E. f alse

Osmolarit y is t he concent rat ion of a solut ion expressed as osmoles of solut e per lit re of solut ion (mosmol/l). Osmolalit y is t he concent rat ion of a solut ion expressed as osmoles of solut e per kg solvent (mosmol/kg). Osmolalit y is independent of t emperat ure and volume t aken up by solut es w it hin t he solut ions. Osmolalit y is t he measure most of t en used clinically, and is est imat ed by depression of f reezing point . Semipermeable membranes allow solvent (f luid) but not solut e (part icles) t o pass t hrough. The osmolalit y of plasma is 290 mosmol/kg H2O. SCC pp 117–122

M CQs

Key Quest ions in Surgical Crit ical Care

137

A 19. A. t rue

B. f alse

C. f alse

D. f alse

E. f alse

Principles of Intensive Care

The kidney has a number of met abolic f unct ions including gluconeogenesis, pept ide hydrolysis and arginine f ormat ion. Each kidney is made up of 1.2 million f unct ional unit s called nephrons. M ost (80% ) of cort ical nephrons have short loops of Henle. The juxt amedullary nephrons (20% ) have long loops of Henle w hich pass int o t he inner medulla, and are primarily concerned w it h t he count ercurrent exchange mechanism t o est ablish a concent rat ion gradient w it hin t he renal medulla. Renal blood f low account s, f or about 20% of cardiac out put (625 ml/min t o each kidney), t his does not change w it h exercise and t here is aut oregulat ion over a range of blood pressures. The cort ex receives t he majorit y of t he renal blood f low, in order t o f orm an ult raf ilt rat e. SCC pp 117–122

A 20. A. f alse

B. f alse

C. f alse

D. t rue

E. t rue

Answ ers

Glomerular f ilt rat ion rat e (GFR) is measured using t he Fick principle f or t he clearance of inulin. Inulin is a polysaccharide of M W 5500 Dalt ons w hich is inject ed int o t he body and f ilt ered. It is not re-absorbed or secret ed by t he kidney, allow ing measurement of urinary inulin t o be used t o calculat e t he f ilt rat ion rat e. Creat inine clearance is used t o give an est imat e of GFR, but since creat inine is secret ed t o a small degree by t he t ubules, it t ends t o over est imat e t he value f or GFR. Renal plasma f low is calculat ed by t he clearance of para-amino hippuric acid (PAH). Renal blood f low is large leading t o small diff erences bet w een art erial and venous blood in oxygen cont ent . Oxygen consumpt ion in t he cort ex is t w ent y t imes t hat in t he medulla due t o act ive t ransport in t he t ubules. SCC pp 117–122

A 21. A. f alse

B. f alse

C. f alse

D. t rue

E. t rue

Renin is released f rom t he juxt aglomerula apparat us in t he renal cort ex. Renin is a prot eolyt ic enzyme t hat is released int o t he plasma w hen t he body sodium cont ent decreases. Renin also exist s in t he brain, heart and adrenal gland. It s subst rat e is an ␣2-globulin, angiot ensinogen, liberat ing an decapept ide (angiot ensin I) and an oct apept ide (angiot ensin II) via 138

M CQs

Key Quest ions in Surgical Crit ical Care

SCC pp 117–122

A 22. A. t rue

B. f alse

C. f alse

D. t rue

E. f alse

Hypert ension can cause a diuresis by increasing medullary blood f low and reducing t he concent rat ion gradient . Carbonic anhydrase inhibit ors e.g. acet ozolamide produce a w eak diuresis w it h high pH, low ammonia and increased bicarbonat e loop diuret ics, such as f rusemide t he Na⫹ Cl ⫺ co-t ransport syst em in t he t hick ascending loop of Henle. Amiloride is not an aldost erone ant agonist (spironolact one is an aldost erone ant agonist ).

Principles of Intensive Care

a convert ing enzyme. Angiot ensin II act s on t he zone glomerulose of the adrenal cortex to liberate aldosterone. This in turn acts on the kidney to increase salt and water retention. Angiotensin II has effects on the cardiovascular, renal and CNS (causing vasoconstriction) and is broken down in the liver.

SCC pp 203–205 Answ ers

M CQs

Key Quest ions in Surgical Crit ical Care

139

Practical Procedures A 1.

A. f alse

B. f alse

C. t rue

Answ ers

D. f alse

E. t rue

Silicone catheters are non-thrombogenic. 10–15% of central venous pressure (CVP) catheters become colonised. The insertion point for a subclavian line is at the junction between the medial 1/3 and the lateral 2/3 of the clavicle. The femoral vein lies within the sheath medial to the artery. SCC pp 211–217

Surgery 2000 18: 2; 56A–C

A 2.

A. t rue

B. t rue

C. t rue

D. t rue

E. f alse

Indicat ions f or int ra-cranial pressure (ICP) monit oring are w hen clinical signs are obscured (drugs), t o assess need f or int ervent ion (head injury, inf ect ion), int ensive care unit (ICU) management of head injury and calculat ion of cerebral perf usion pressure (CPP) CPP ⫽ mean art erial pressure ⫺ ICP

ICP measurement can be ext radural, subdural, subarachnoid or via a lat eral vent ricle cat het er. Surgical Crit ical Care Ashf ord R, Evans N. GM M Lt d. London, 2001.

SCC pp 225–227

A 3.

A. t rue

B. f alse

C. t rue

D. f alse

E. t rue

Tracheo-innominat e art ery erosion (TIAE) carries a mort alit y w hen t reat ed urgent ly by ligat ion of t he TIA of 75% . The ant erior jugular vein is t he vein most likely t o cause bleeding problems. Ot her complicat ions: 䊏 䊏

140

M CQs

IM M ED: haemorrhage, air embolus, local st ruct ure damage, apnoea, misplacement Cont inuing care: inf ect ion, t racheit is, t racheal st enosis & necrosis, t ube blockage/displacement , surgical

Key Quest ions in Surgical Crit ical Care

emphysema, pneumot horax, decannulat ion problems and f ist ulae Surgical Crit ical Care Ashf ord R, Evans N. GM M Lt d. London, 2001.

A 4.

A. f alse

B. t rue

C. t rue

D. t rue

E. f alse

The cricot hyroid membrane is superior t o t he cricoid cart ilage, inf erior t o t he t hyroid cart ilage. Emergency procedures have a complicat ion rat e f ive t imes t hat of elect ive. SCC pp 220–221

A 5.

A. t rue

B. t rue

C. t rue

D. t rue

Practical Procedures

SCC pp 217–220

E. t rue

All t he above plus AV f ist ula, drugs being given in error t hrough it , and compromise t o dist al f low as w ell as inf ect ion. SCC pp 211–217

A. t rue

B. f alse

C. f alse

D. f alse

E. f alse

The int ernal jugular vein (IJV) is int imat ely associat ed w it h t he carot id art ery t hroughout it s course, lying init ially post erior t o it and t hen ant ero-lat eral w it hin t he carot id sheat h. The IJV is superf icial in t he upper part of it s course, covered by st ernomast oid muscle in t he middle t hird is again superf icial in t he low er t hird as it split s t he st ernal and clavicular heads of t hat muscle. Cannulat ion of t he middle t hird requires t he operat or t o t raverse t he st ernomast oid muscle w hich can be unpleasant f or t he pat ient w hen aw ake. Arrhyt hmias occur because of guide w ire st imulat ion of t he right at rium and vent ricle and is equally likely if t he w ire is advanced t oo f ar. Elect rocardiogram (ECG) monit oring should alw ays be available f or t his reason during cent ral line insert ion.

Answ ers

A 6.

SCC pp 211–214

A 7.

A. f alse

B. f alse

C. f alse

D. f alse

E. t rue

In pat ient s w it h cerebral impairment and raised ICP, head neut ral or head dow n t ilt should be limit ed t o t he minimum possible f or t he procedure. How ever cont inuing w it h head up t ilt

M CQs

Key Quest ions in Surgical Crit ical Care

141

Practical Procedures

risks t he development of air embolus, part icularly if t he pat ient is dehydrat ed and should never be at t empt ed. A low approach t o t he IJV reduces t he chance of art erial punct ure but increases t he incidence of pneumot horax. The subclavian approach should not be at t empt ed if t he pat ient has a bleeding diat hesis since it cannot be compressed in cases of vessel rupt ure. The ext ernal jugular vein (EJV) has valves w hich prohibit t he passage of a guide w ire. IJV on t he right side is t he sit e of choice but a cat het er placed t oo f ar w ill risk int ra-cardiac rupt ure. SCC pp 211–214

Answ ers

142

M CQs

Key Quest ions in Surgical Crit ical Care

Section 2 – Vivas Cardiovascular Syst em – Quest ions ..........................................................145 Respirat ory Syst em – Quest ions ................................................................147 Ot her Syst ems and M ult isyst em Failure – Quest ions ..............................149 Problems in Int ensive Care – Quest ions....................................................151 Principles of Int ensive Care – Quest ions ..................................................152 Pract ical Procedures – Quest ions ..............................................................153 Cardiovascular Syst em – Answ ers..............................................................155 Respirat ory Syst em – Answ ers ..................................................................170 Ot her Syst ems and M ult isyst em Failure – Answ ers..................................202 Problems in Int ensive Care – Answ ers ......................................................223 Principles of Int ensive Care – Answ ers......................................................225 Pract ical Procedures – Answ ers ................................................................230

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Cardiovascular System

Quest ions

Q 1.

What clinical features may indicate poor peripheral perfusion?

Q 2.

What complications may arise following thoracic surgery?

Q 3.

What post-operative arrhythmias commonly occur following cardiac surgery and how would you manage them?

Q 4.

What are the causes of pulseless electrical activity (PEA)?

Q 5.

What are the causes of anaemia in the critically ill patient and when would you transfuse them?

Q 6.

What is Starling’s Law of the heart?

Q 7.

What information can be obtained by pulmonary artery catheterisation in the critically ill patient?

Q 8.

What are the indications for pulmonary artery catheterisation in the critically ill patient?

Q 9.

What are the complications of blood transfusion?

Q 10. How would you manage the acute onset of atrial fibrillation (AF)? Q 11. How would you treat acute pulmonary oedema? Q 12. How would you manage the acutely unwell patient with sudden onset chest pain radiating to the back and an absent right brachial and radial pulse? Q 13. Define disseminated intravascular coagulation (DIC). What are the causes and what haematological results would you expect in DIC?

Vivas

Key Quest ions in Surgical Crit ical Care

145

Q 14. What are the indications for an intra-aortic balloon pump (IABP)?

Cardiovascular System

Q 15. What are the potential complications of central vein cannulation? Q 16. How would you optimise cardiac output in the hypotensive patient?

Quest ions

146

Vivas

Key Quest ions in Surgical Crit ical Care

Respiratory System

Quest ions

Q 1.

How would you interpret a chest radiograph in a critically ill surgical patient?

Q 2.

How would you diagnose adult respiratory distress syndrome (ARDS) in a ventilator dependent post-operative surgical patient?

Q 3.

How is respiration controlled?

Q 4.

What is involved in initiating a breath?

Q 5.

How is respiration affected by a) exercise b) general anaesthesia c) hypovolaemia d) altitude?

Q 6.

What is functional residual capacity (FRC) and why is it important?

Q 7.

What is measured using a spirometer?

Q 8.

What dynamic tests of respiratory function do you know?

Q 9.

What is meant by respiratory compliance?

Q 10. How do ventilation and perfusion vary with spontaneous and mechanical ventilation? What do you understand by the terms ‘shunt’ and ‘dead space’? Q 11. How would you go about interpreting arterial blood gas (ABG) analysis? Q 12. How would you classify hypoxia? Q 13. Which patients are at risk of post-operative hypoxaemia? What methods are available to deliver oxygen to a spontaneously breathing patient after surgery? Q 14. How would you classify respiratory failure, and what are the signs? Q 15. What are the indications for intubation and mechanical ventilation?

Vivas

Key Quest ions in Surgical Crit ical Care

147

Q 16. What are the effects of mechanical ventilation? Q 17. What modes of mechanical ventilation do you know? Which of these modes are used for weaning?

Respiratory System

Q 18. Why is it important to maintain adequate lung volume? What methods do you know for optimising lung volume? Q 19. What factors affect the ability to wean from mechanical ventilation? Q 20. What are the causes of airway obstruction? How may these be managed? Q 21. What are the principle causes of ARDS? What clinical findings make up the diagnosis? Q 22. Describe the pathophysiological processes responsible for ARDS? What is the prognosis?

Quest ions

148

Q 23. What are the objectives for respiratory support in a patient with ARDS? What mechanisms are there to maintain adequate oxygenation?

Vivas

Key Quest ions in Surgical Crit ical Care

Other Systems and Multisystem Failure

Quest ions

Q 1.

What are the indications for a computed tomography (CT) scan following a head injury?

Q 2.

What type of injuries are possible to blood vessels and what are their sequelae?

Q 3.

What are the causes of raised intracranial pressure (ICP) after head injury?

Q 4.

What are the indications for urgent surgical exploration in thoracic trauma?

Q 5.

How do you decide how much fluid to give a patient with major burns?

Q 6.

How do you diagnose and treat fat embolism syndrome (FES)?

Q 7.

What features of burn injuries would make you suspect an inhalational injury and how would you manage it?

Q 8.

How would you assess the severity of a head injury?

Q 9.

What are the causes of massive haemoptysis and how would you manage a patient with it?

Q 10. How would you manage a patient with acute hepatic failure (AHF)? Q 11. What are the clinical features of a raised ICP? Q 12. How would you manage a patient with a spinal cord injury? Q 13. What methods are employed to try to prevent multi-organ dysfunction syndrome (MODS)? Q 14. How would you manage a patient with a severe upper gastrointestinal bleed? Q 15. How would you manage a patient with blunt chest trauma?

Vivas

Key Quest ions in Surgical Crit ical Care

149

Other Systems and Multisystem Failure

Q 16. What is systemic inflammatory response syndrome (SIRS) and how would you diagnose it? Q 17. What is MODS? Q 18. What are the principles of management in MODS? Q 19. What are the advantages and disadvantages of enteral nutrition? Q 20. What are the advantages and disadvantages of parenteral nutrition? Q 21. How may nutrition regimens be tailored to patients with organ dysfunction? Q 22. What are the daily nutritional requirements of patients and how may these vary with critical illness?

Quest ions

150

Vivas

Key Quest ions in Surgical Crit ical Care

Problems in Intensive Care

Quest ions

Q 1.

What are the differences between sepsis, severe sepsis and septic shock?

Q 2.

What are the features of occult intra-abdominal sepsis and how would you diagnose and treat it?

Vivas

Key Quest ions in Surgical Crit ical Care

151

Principles of Intensive Care

152

Quest ions

Q 1.

What are the principles for the safe transfer of the critically ill surgical patient?

Q 2.

What are the basics of successful clinical monitoring of the critically ill patient?

Q 3.

What parameters would make you consider early referral to critical care?

Q 4.

What are the principles of analgesia in the multiple injured patient?

Q 5.

What reasons might you want a surgical patient to go to intensive therapy unit (ITU) electively?

Q 6.

What is meant by scoring systems for intensive care unit (ICU) patients? What scoring systems do you know?

Vivas

Key Quest ions in Surgical Crit ical Care

Practical Procedures

Quest ions

Q 1.

What are the complications of inserting an intercostal chest drain?

Q 2.

What are the indications for tracheostomy and what are its advantages?

Q 3.

Describe how you would perform a venous cut-down of the long saphenous vein at the ankle.

Q 4.

What are the findings for a diagnostic peritoneal lavage (DPL) to be positive?

Q 5.

Why might you consider monitoring intra-abdominal pressure (IAP)?

Q 6.

What is a chest drain and how does it function?

Q 7.

What are the indications and potential complications of central venous cannulation?

Q 8.

Outline the relevant anatomy of a) the internal jugular vein (IJV) and b) the subclavian vein. Describe the technique used to cannulate each of these central veins.

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Cardiovascular System

Answ ers

Q 1.

What clinical features may indicate poor peripheral perfusion?

A 1.

Classically poor peripheral perf usion is indicat ed by cool clammy skin w it h poor capillary f illing and collapsed veins. Ot her indicat ors are conf usion, decreased peripheral t emperat ure, oliguria or anuria, met abolic acidosis, a low volume pulse and peripheral cyanosis. SCC pp 15–20

Q 2.

What complications may arise following thoracic surgery?

A 2.

Intrathoracic bleeding Usually occurs f rom lung parenchyma or bronchial vessels and may present w it h clinical f eat ures of hypovolaemia. It is usually det ect able f rom drains. Re-operat ion is required if t here is rapid blood loss via chest drain, a signif icant int rapleural collect ion on chest X-ray, persist ing hypovolaemia despit e t ransf usion or hypoxia due t o compression of t he underlying lung. Sputum retention and atelectasis Present s as t achypnoea and hypoxia. Examinat ion usually show s reduced bilat eral basal air ent ry. Prevent ion is pref erred t o t reat ment . The mainst ay of t reat ment is chest physiot herapy, but t racheost omy and suct ion may be required. Ant ibiot ics are reserved f or t hose w it h proven pneumonia. Air leak These present s as a persist air leak or bubbling of chest drain and usually set t le spont aneously over 2–3 days. They may require suct ion on pleural drains. Apposit ion of lung t o pariet al pleura encourages eff icient healing. Bronchopleural fistula Fist ulae are seen in 2% of pat ient s undergoing pneumonect omy. They usually occur as a result f orm a leak f rom a sut ure line, and

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Cardiovascular System

occurs part icularly in t hose w it h f act ors impairing w ound healing. They most commonly occur 7–10 days af t er surgery present ing w it h sudden breat hlessness and expect orat ion of bloodst ained f luid. Treat ment is t o lie t he pat ient w it h operat ed side dow nw ards, oxygen and chest drain, t horacot omy and repair of f ist ula may also be required. SCC pp 49–55

What post-operative arrhythmias commonly occur following cardiac surgery and how would you manage them?

A 3.

At rial t achyarrhyt hmias occur w it h an incidence of bet w een 17 and 33% , and generally occur bet w een days 2 and 3. At rial f ibrillat ion (AF) is t he most common, is usually sympt omat ic but of t en self -limit ing. It may cause haemodynamic compromise or t hromboembolic event s. The t reat ment depends on haemodynamics. For t he haemodynamically st able a ␤-blocker is indicat ed, f or t he haemodynamically unst able, DC cardioversion is employed f irst t hen rat e cont rol drugs (met oprolol, digoxin, verapamil).

Answ ers

Q 3.

Sust ained vent ricular t achyarrhyt hmias are uncommon af t er surgery (0.4–1.4% ). These arrhyt hmias are associat ed w it h haemodynamic inst abilit y, elect rolyt e dist urbances, hypoxia and graf t occlusion. These are associat ed w it h poorer short and long t erm prognosis w it h a hospit al mort alit y of upt o 50% . Acut e t reat ment may require lidocaine or amiodarone. Vent ricular t achycardia may progress t o vent ricular f ibrillat ion requiring def ibrillat ion. Isolat ed premat ure vent ricular complexes are not uncommon, of t en associat ed w it h elect rolyt e imbalance and do not require acut e t reat ment . SCC p 51

156

Q 4.

What are the causes of pulseless electrical activity (PEA)?

A 4.

Pulseless elect rical act ivit y (PEA) w as know n as elect romechanical dissociat ion (EM D). It is t he presence of an elect rical cardiac rhyt hm in t he absence of a cardiac out put . Causes are divided int o primary and secondary (Table 1.1)

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Table 1.1 Primary and secondary causes of PEA Primary PEA

Tension pneumot horax Hypovolaemic shock Cardiac t amponade Pulmonary embolus Cardiac rupt ure

SCC pp 11–15

What are the causes of anaemia in the critically ill patient and when would you transfuse them?

A 5.

Anaemia can be due t o bleeding (occult or overt ), anaemia of crit ical illness, or in t he very young due t o repeat ed blood sampling. Occult bleeding can be int o t he skull, t horax, abdomen, ret roperit oneal space, pelvis, limbs f or closed long bone f ract ures or at t he scene of an accident . Anaemia of crit ical illness is due t o bone marrow suppression, decreased eryt hropoet in product ion or an impaired bone marrow response t o eryt hropoet in.

Answ ers

Q 5.

Cardiovascular System

M yocardial inf arct ion Drugs 䊏 ␤-blockers 䊏 Calcium ant agonist s Elect rolyt e imbalance 䊏 Hyperkalaemia 䊏 Hypocalcaemia

Secondary PEA

Transfusion is necessary when there is evidence of impaired perfusion. There is no single transfusion trigger figure but the following give an idea when transfusion is necessary: haemoglobin, haematocrit, ongoing haemorrhage, symptomatic anaemia, perfusion impairments and impaired oxygenation. A lower threshold for transfusion is necessary with extremes of age. SCC pp 36–41

Q 6.

What is Starling’s Law of the heart?

A 6.

St arling’s Law describes t he relat ionship bet w een preload or f illing pressure and st roke volume. The f orce of myocardial muscle cont ract ion is proport ional t o t he amount of st ret ch in t he cardiac muscle f ibres prior t o cont ract ion. Thus, in t he normal heart st roke, volume increases as t he end-diast olic volume increases (Fig. 1.1). The vent ricular f unct ion curve is displaced upw ards (increased cont ract ilit y) by sympat het ic act ivat ion including posit ive inot ropes (e.g. dobut amine, adrenaline) and displaced dow nw ards (decreased cont ract ilit y) by hypoxia,

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Sympat het ic act ivat ion

Cardiovascular System

St roke volume Normal heart

Failing heart

Filling Pressure (Pre-load)

Fig. 1.1 Vent ricular f unct ion curves demonst rat ing t he relat ionship bet w een st roke volume and preload in t he normal, f ailing and st imulat ed heart .

Answ ers

acidosis and negat ively inot ropic drugs (e.g. ␤-blockers and calcium ant agonist s). The relat ionship bet w een preload and st roke volume persist s in t he f ailing heart . Indeed, it act s as one of t he compensat ory mechanisms in heart f ailure t hat init ially maint ains st roke volume. A reduced st roke volume result s in an increased amount of blood in t he vent ricle at end-diast ole. The amount of st ret ch w it hin t he vent ricular muscle f ibres is t heref ore increased and t hrough St arling’s Law, myocardial cont ract ilit y is increased, rest oring st roke volume. In t he f ailing heart , how ever, t he lef t vent ricular f unct ion curve is f lat t ened (Fig. 1.1) such t hat increasing lef t at rial f illing pressure, t he preload of t he lef t vent ricle, (above about 20 mmHg) does not produce a f urt her increase in st roke volume, but does predispose t o t he development of pulmonary venous hypert ension and pulmonary oedema. SCC pp 3–4

158

Q 7.

What information can be obtained by pulmonary artery catheterisation in the critically ill patient?

A 7.

During cat het erisat ion of t he right heart and pulmonary art ery, pressures are t ransduced direct ly f rom t he cat het er t ip t hrough

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The CVP and t he PAOP provide an object ive measure of t he f illing pressure or preload of t he right and lef t vent ricles, respect ively. Right vent ricular and pulmonary art ery pressure indicat e w het her or not pulmonary hypert ension is present . A ‘st ep-up’ in blood oxygen sat urat ions bet w een t he right at rium and right vent ricle indicat es t hat oxygenat ed blood is ent ering t he right vent ricle (a lef t t o right shunt ) and is consist ent w it h a vent ricular sept al def ect (VSD), w hich may occur acut ely af t er myocardial inf arct ion.

Answ ers

Cardiac out put is est imat ed by t hermodilut ion. A know n volume (t ypically 10 ml) of cold cryst alloid is inject ed int o t he right at rial port of t he pulmonary art ery cat het er. A t hermist or at t he cat het er t ip measures t he result ant t ransient t emperat ure decrease in t he pulmonary art ery. The area under t he curve w hen f all in t emperat ure is plot t ed against t ime correlat es w it h cardiac out put , w hich is calculat ed by comput er.

Cardiovascular System

t he f luid-f illed lumen: cent ral venous pressure (CVP), right vent ricular pressure, pulmonary art ery pressure, pulmonary art ery occlusion pressure (PAOP). Blood can be aspirat ed f rom t he dist al port or t he right at rial port of t he cat het er t o measure blood oxygen sat urat ions f rom t he right heart and pulmonary art ery. Cardiac out put and syst emic vascular resist ance (SVR) can be est imat ed indirect ly f rom inf ormat ion gained during right heart cat het erisat ion.

SVR can be calculat ed f rom aort ic pressure, right at rial pressure and cardiac out put . SVR =

80 (mean aortic pressure − mean right atrial pressure) cardiac output SCC pp 18–20

Q 8.

What are the indications for pulmonary artery catheterisation in the critically ill patient?

A 8.

The indicat ions f or pulmonary art ery cat het erisat ion can be broadly divided int o scenarios requiring measurement of t he PAOP, cardiac out put and SVR, and blood oxygen sat urat ions (see Quest ion 2 in t his sect ion and Table 1.2).

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Table 1.2 Indicat ions f or pulmonary art ery cat het erisat ion

Cardiovascular System

M easurement of PAOP t o det ermine volume st at us and opt imise cardiac out put : 䊏 Oliguria 䊏 Hypot ension 䊏 RV inf arct ion 䊏 Cardiogenic shock 䊏 Sept ic shock 䊏 Adult respirat ory dist ress syndrome (ARDS) M easurement of cardiac out put /SVR t o guide inot ropic t herapy: 䊏 Cardiogenic shock 䊏 Sept ic shock M easurement of right heart blood O2 sat urat ions: 䊏 Diagnosis of lef t t o right shunt (VSD) 䊏 M ixed venous (PA) O2 concent rat ion needed f or some measures of cardiac out put

Answ ers

PAOP The accurat e assessment of volume st at us is cent ral t o t he appropriat e management of t he crit ically ill pat ient . M easurement of t he PAOP is t heref ore indicat ed w hen volume st at us remains uncert ain af t er clinical evaluat ion. Clinical assessment of volume st at us may be part icularly diff icult in t he presence of chronic lung disease and t ricuspid regurgit at ion. Furt hermore, if t here is a disparit y bet w een t he f unct ion of t he right and lef t vent ricle (right vent ricular inf arct ion, pulmonary embolism, cor pulmonale, lef t vent ricular disease), t he f illing pressure of t he right heart (CVP) may not ref lect t he f illing pressure of t he lef t heart . In t hese circumst ances, t he CVP w ill not be an accurat e guide t o volume st at us and measurement of t he PAOP is indicat ed. A normal PAOP is about 8–12 mmHg. A low value implies hypovolaemia. Pulmonary oedema in t he presence of a low PAOP indicat es ARDS. An elevat ed PAOP implies volume overload. In addit ion t o it s diagnost ic purpose, PAOP can also be used t o guide f luid administ rat ion in pat ient s w ho are at risk of developing volume overload such as t he elderly or t hose w it h a hist ory of heart disease.

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SVR In t he clinical set t ing, t he det erminat ion of SVR is of t en used t oget her w it h cardiac out put and PAOP t o assist in t he diagnosis of t he shocked pat ient (Table 1.3). A low SVR is charact erist ic of sept ic shock, w hile t he SVR is usually raised in cardiogenic shock and hypovolaemia. Serial measurement s of PAOP, cardiac out put and SVR can be used t o monit or t he eff ect s of f luid administ rat ion and inot ropic t herapy.

Answ ers

Blood oxygen saturations The diff erent ial diagnosis of t he pat ient in cardiogenic shock af t er acut e myocardial inf arct ion includes VSD and mit ral regurgit at ion due t o papillary muscle rupt ure. Diff erent iat ing bet w een t he t w o may be diff icult because bot h cause similar clinical present at ions and a pansyst olic murmur. If t he diagnosis cannot be made by echo, t hen blood oxygen sat urat ions can be measured f rom t he right vent ricle and right at rium. A ‘st ep-up’ in oxygen sat urat ion in t he right vent ricle (oxygen sat urat ion higher t han t he right at rium) w ould be consist ent w it h a VSD.

Cardiovascular System

Cardiac output M easurement of cardiac out put is usef ul bot h as a diagnost ic aid and t o monit or t herapy in t he crit ically ill pat ient . A low cardiac out put in t he hypot ensive pat ient is consist ent w it h cardiogenic shock and indicat es t he need f or inot ropic support , w hile a high cardiac out put is consist ent w it h sept ic shock.

M ixed venous (pulmonary art ery) blood oxygen sat urat ion measurement is required f or est imat ion of cardiac out put by t he Fick met hod. Table 1.3 The diff erent ial diagnosis of shock using haemodynamic paramet ers obt ained f rom Sw an-Ganz cat het erisat ion

Hypovolaemia Cardiogenic shock Sept ic shock

PAOP

Cardiac index

SVR

↓ ↑ ↓

↓ ↓ ↑

↑ ↑ ↓

PAOP ⫽ pulmonary art ery occlusion pressure; SVR ⫽ syst emic vascular resist ance; Normal values: PCWP 8–12 mmHg; Cardiac index 2.5–4.0 l/min/m 2; SVR 770–1500 dynes s/cm 5

SCC pp 18–20

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What are the complications of blood transfusion?

A 9.

The possible complicat ions of blood t ransf usion are: precipit at ion of heart f ailure, f ebrile react ion, haemolyt ic t ransf usion react ion, t ransmission of inf ect ion, hyperkalaemia, hypocalcaemia, t hrombocyt openia, disseminat ed int ravascular coagulat ion (DIC), hypot hermia.

Cardiovascular System

Q 9.

Haemolyt ic t ransf usion react ions are usually due t o ABO incompat ibilit y caused by administ rat ive error. They should be managed by st opping t he blood t ransf usion, checking pat ient ident it y against t he blood unit , ret urning t he blood unit t o t he haemat ology laborat ory w it h a sample of clot t ed blood and et hylene diamint et raacet ic acid (EDTA) sample. Severe react ions may require t he administ rat ion of f luid, adrenaline, ant ihist amine and st eroids as f or anaphylact ic shock. M ilder f ebrile react ions are usually due t o ant ibodies against w hit e cells.

Answ ers

A number of inf ect ions (viruses, bact eria, prot ozoa) can be t ransmit t ed by blood t ransf usions. M ost concern surrounds t he t ransmission of viral inf ect ions including hepat it is B & C, human immunodef iciency virus (HIV), Epst ein-Barr virus (EBV), and cyt omegalo virus (CM V). Ant ibodies against hepat it is B & C, and HIV are screened f or in blood donat ed in t he UK. M assive t ransf usion (def ined as a t ransf usion volume equal t o t he pat ient ’s ow n blood volume w it hin 24 hours) may be associat ed w it h several complicat ions. St ored blood cont ains f ew plat elet s and reduced concent rat ions of f act ors V and VIII. ‘Dilut ional’ t hrombocyt openia and clot t ing f act or def iciency may t heref ore occur during massive t ransf usion. The plat elet count , INR and act ivat ed part ial t hromboplast in t ime (APTT) should be monit ored, and t he administ rat ion of plat elet s and f resh f rozen plasma may be required. The plasma pot assium concent rat ion increases during st orage as pot assium leaks out of t he red cells. Plasma calcium levels may be reduced by binding of ionised calcium by cit rat e added t o st ored blood. Hypocalcaemia and hyperkalaemia may t heref ore occasionally result af t er massive t ransf usion. Hypot hermia may result f rom t he rapid t ransf usion of blood and blood w armers should be used during rapid massive t ransf usion. SCC pp 38–41

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Q 10. How would you manage the acute onset of atrial fibrillation (AF)?

M anagement includes t he ident if icat ion and correct ion of reversible causes such as elect rolyt e imbalance. Furt her management depends upon w het her haemodynamic compromise is present and on t he vent ricular rat e. If signif icant haemodynamic compromise is t hought t o be caused by t he new occurrence of AF, t hen DC cardioversion should be perf ormed urgent ly.

I

aVR

V1

V4

II

aVL

V2

V5

III

aVF

V3

V6

Answ ers

If t he pat ient is not signif icant ly compromised, t hen he can eit her be managed w it h vent ricular rat e cont rol or by elect ive cardioversion. Digoxin, ␤-blockers and verapamil can be used f or rat e cont rol. Cardioversion may be at t empt ed chemically or elect rically. A number of ant i-arrhyt hmic drugs can be used t o cardiovert AF t o sinus rhyt hm, but success is limit ed and t hey all carry t he risk of pro-arrhyt hmia, part icularly if t he heart is not st ruct urally normal. Amiodarone and ␤-blockers are t he saf est drugs in t he st ruct urally abnormal heart . DC cardioversion carries a higher success rat e. Cardioversion can be perf ormed w it hout ant icoagulat ion if t he onset of AF occurred w it hin 48 hours, as

Cardiovascular System

A 10. AF is characterised by the absence of a P wave before each QRS complex and irregularity of the ventricular (QRS) response (Fig. 1.2).

II

Fig. 1.2 Elect rocardiogram (ECG) demonst rat ing at rial f ibrillat ion.

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t he risk of lef t at rial t hrombus f ormat ion is low w it hin t his t ime f rame. Thereaf t er, 4 w eeks of w arf arin prior t o cardioversion (as an out pat ient ) is recommended. All pat ient s w it h persist ent AF, except t hose aged ⬍65 years w it h lone AF, should be considered f or w arf arin t o prevent st roke. SCC pp 20–21

Q 11. How would you treat acute pulmonary oedema?

Answ ers

A 11. Reassure t he pat ient . Sit him up. M onit or ECG and oxygen sat urat ions. Administ er high f low oxygen via a rebreat hing bag. Give int ravenous opiat e (e.g. diamorpine 2.5–5 mg) and ant i-emet ic (e.g. met aclopramide 10 mg). Opiat es act as venodilat ors, reducing preload, and also as an anxiolyt ic. Administ er int ravenous diuret ic (e.g. f rusemide 40 mg). Acut ely, t his act s as a venodilat or prior t o t he onset of it s diuret ic eff ect . If t he pat ient is not hypot ensive, init iat e an int ravenous nit rat e inf usion. Again, t his causes vasodilat at ion and reduces preload. As pulmonary venous pressure f alls t o t he t hreshold at w hich plasma oncot ic pressure f avours resorpt ion of f luid, pulmonary oedema begins t o resolve. If t he pat ient is hypot ensive (cardiogenic shock), inot ropes (e.g. dobut amine 2.5–15 ␮g/kg/min) should be init iat ed. The dose is t ailored t o achieve a blood pressure capable of perf using t he major organs. Clinically, t his is ref lect ed by a sat isf act ory urine out put . SCC pp 33–35

Q 12. How would you manage the acutely unwell patient with sudden onset chest pain radiating to the back and an absent right brachial and radial pulse? A 12. The likely diagnosis is aort ic dissect ion, but myocardial ischaemia w it h right subclavian art ery st enosis due t o at herosclerosis, and emboli t o t he brachial art ery and a coronary art ery due t o lef t at rial t hrombus or endocardit is, are possible. M onit oring of vit al signs, ECG and oxygen sat urat ions should be perf ormed. Oxygen and opiat e analgesia should be administ ered. Examinat ion of t he pat ient should f ocus on det ermining t he cont ralat eral BP, t he presence or absence of t he ot her peripheral pulses and of aort ic regurgit at ion. 164

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Answ ers

The def init ive diagnosis is usually made by eit her cont rast enhanced CT scan, magnet ic resonance imaging (M RI) or t ransoesophageal echo (TOE). This depends largely on local availabilit y and expert ise. CT scanning is readily available and non-invasive. M RI t ends t o be less readily available and it present s diff icult ies in monit oring of t he acut ely ill pat ient . TOE requires an experienced operat or, but can be perf ormed on t he w ard or in t he anaest het ic room and provides addit ional inf ormat ion about t he presence of aort ic regurgit at ion, pericardial eff usion, lef t vent ricular f unct ion and relat ionship of t he coronary ost ea t o t he dissect ion f lap. Aort ography is now rarely used because it is invasive and pot ent ially complicat ed by cat het ers ent ering t he f alse lumen.

Cardiovascular System

Blood t est s w ill include f ull blood count (FBC), U & E, and cross-mat ch. Init ial invest igat ions may provide support ive evidence f or t he diagnosis of aort ic dissect ion. A 12-lead ECG should be perf ormed. How ever, any of t hese scenarios may produce ST segment changes of ischaemia or inf arct ion. In aort ic dissect ion, t his is caused if a coronary art ery ost ium is disrupt ed by t he dissect ion f lap. Transt horacic echo may demonst rat e t he dissect ion f lap, and w ill also demonst rat e t he presence of aort ic regurgit at ion and pericardial eff usion, bot h consist ent w it h aort ic dissect ion. CXR may reveal a w idened mediast inum and/or a pericardial eff usion in cases of aort ic dissect ion.

Furt her management is dependent upon t he sit e of t he dissect ion. St anf ord t ype A dissect ions involve t he ascending aort a and are managed surgically, w hile t ype B dissect ions do not involve t he ascending aort a and are managed medically unless complicat ions ensue. The mainst ay of medical management is cont rol of blood pressure using agent s such as int ravenous labet alol and sodium nit roprusside t o obt ain acut e cont rol of BP (t arget 100–120 mmHg syst olic), w it h t he addit ion of oral agent s (e.g. ␤-blockers, calcium blockers, ACE inhibit ors) t hereaf t er. If dist al dissect ion is complicat ed by rupt ure, aneurysm f ormat ion, vit al organ or limb ischaemia, cont inued pain, or ret rograde progression int o t he ascending aort a, t hen surgery is indicat ed. SCC pp 26–27

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Q 13. Define disseminated intravascular coagulation (DIC). What are the causes and what haematological results would you expect in DIC?

Cardiovascular System

A 13. DIC is charact erised by act ivat ion of t he clot t ing cascades w it h generat ion of f ibrin, consumpt ion of clot t ing f act ors and plat elet s, and secondary act ivat ion of f ibrinolysis leading t o product ion of f ibrinogen degradat ion product s (FDPs). Clinically, it may be asympt omat ic manif est only on blood invest igat ions, or may cause bleeding, or t issue ischaemia due t o vessel occlusion by f ibrin and plat elet s. DIC may be caused by Gram-negat ive, meningococcal and st aphylococcal sept icaemia, t issue damage af t er t rauma, burns or surgery, malignancy, haemolyt ic blood t ransf usion react ions, f alciparum malaria, snake bit es, and obst et ric condit ions such as placent al abrupt ion and amniot ic f luid embolism.

Answ ers

The prot hrombin t ime (or INR), APTT, and t hrombin t ime are prolonged. The f ibrinogen level and plat elet count are low. High levels of FDPs are present . There may be f ragment ed red cells on t he blood f ilm due t o red cell damage during passage t hrough f ibrin w ebs in t he circulat ion. SCC pp 47–49

Q 14. What are the indications for an intra-aortic balloon pump (IABP)? A 14. The int ra-aort ic ballon pump (IABP) augment s diast olic pressure and reduces af t erload result ing in increased coronary and cerebral perf usion and a reduct ion in myocardial oxygen demand. The main indicat ion f or an IABP is support ive t herapy prior t o a def init ive procedure. M ost commonly, t his is in t he haemodynamically compromised pat ient w it h a post -myocardial inf arct VSD or mit ral regurgit at ion due t o papillary muscle rupt ure, or in a pat ient w it h ongoing myocardial ischaemia despit e maximal medical t herapy as a bridge t o coronary angioplast y or coronary art ery bypass graf t surgery. IABP may also be used post -operat ively, usually af t er cardiac surgery, in pat ient s w it h lef t vent ricular dysf unct ion. IABP may also be placed prophylact ically in high-risk coronary angioplast y. IABP is

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cont ra-indicat ed in pat ient s w it h signif icant aort ic regurgit at ion (w hich it exacerbat es), aort ic dissect ion, aort ic aneurysm, and severe peripheral vascular disease. SCC p 8

A 15. These are: 䊏 䊏 䊏 䊏 䊏 䊏

art erial punct ure, w hich may result in haemot horax pneumot horax inf ect ion (localised or syst emic) endocardit is (w it h chronic cent ral venous cannulat ion) neurological injury air embolism.

Cardiovascular System

Q 15. What are the potential complications of central vein cannulation?

SCC pp 211–214 Answ ers

Q 16. How would you optimise cardiac output in the hypotensive patient? A 16. The specif ic management of t he hypot ensive pat ient is clearly part ly dependent upon t he cause of t he haemodynamic compromise. For example, if t he hypot ension is secondary t o haemorrhage, t hen volume replacement w it h blood is t he t reat ment . The commonest cause of cardiogenic shock is acut e myocardial inf arct ion, w hich is managed w it h aspirin, coronary reperf usion by t hrombolysis or angioplast y, and inot ropes. In t he crit ically ill pat ient , hypot ension may be mult if act orial w it h hypovolaemia, sepsis and lef t vent ricular dysf unct ion cont ribut ing. Cert ain principles of support ive management can be out lined. Assess and optimise volume status Clinical assessment of volume st at us comprises searching f or a hist ory of blood or volume loss, examining t he pat ient f or signs of hypovolaemia or volume overload, examining f luid balance chart s, and review ing a CXR (Table 1.4).

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Table 1.4 Clinical assessment of volume st at us in t he hypot ensive or oliguric pat ient Hypovolaemia

Volume overload

Cardiovascular System

Hist ory

Poor int ake or volume loss, e.g. GI bleed, vomit ing

Know n heart f ailure or suggest ive hist ory

Examinat ion

Post ural hypot ension, jugular venous pressure (JVP)↓, clear lungs, no oedema

JVP↑, S3, crepit at ions, oedema

Fluid balance

Negat ive

Posit ive

CXR

No pulmonary oedema

Pulmonary oedema

S3 ⫽ t hird heart sound.

Answ ers

Invasive monitoring If volume st at us remains uncert ain af t er clinical assessment , CVP and/or Sw an-Ganz cat het er insert ion is indicat ed. In most circumst ances, a right -sided f illing pressure (CVP) of 10–12 mmHg and a lef t -sided f illing pressure (PAOP) of 16–18 mmHg indicat es an appropriat e preload t o opt imise cardiac out put . If t he f illing pressure is t oo low, f luid should be administ ered unt il t he PAOP is opt imised. Assess the need for inotropes Inot ropes are indicat ed if hypot ension is present in t he presence of a high PAOP (i.e. t he pat ient is volume overloaded or in cardiogenic shock), or if hypot ension persist s af t er correct ion of hypovolaemia. Assessment of cardiac out put and SVR may assist in t he diagnosis of t he cause of shock (Table 1.3) and in t he choice of t he appropriat e inot ropes. In cardiogenic shock, t he cardiac out put is low and SVR high. In t heory t heref ore t he ideal inot rope in t hese circumst ances w ould increase cardiac out put w hile decreasing SVR. Dobut amine has t hese propert ies, at least at low er doses. At higher doses, vasoconst rict ion and an increase in SVR can occur. In sept ic shock, cardiac out put is usually high and SVR low. Vasoconst rict ing inot ropes e.g. adrenaline or noradrenaline are appropriat e.

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Treat associated arrhythmias Arrhyt hmias, part icularly AF, are common in t he crit ically ill pat ient . If t he main cause of haemodynamic compromise is t hought t o be t he new occurrence of AF, t hen DC cardioversion should be perf ormed urgent ly. Agent s such as amiodarone can be used in an at t empt t o maint ain sinus rhyt hm. M ore commonly, AF is one of a number of cont ribut ing f act ors and can be managed by cont rol of t he vent ricular response rat e w it h drugs such as digoxin.

Cardiovascular System

Assess the need for IABP IABP insert ion is part icularly indicat ed as support ive t herapy prior t o a def init ive procedure e.g. in a pat ient w it h a post -myocardial inf arct VSD or mit ral regurgit at ion due t o papillary muscle rupt ure.

Table 1.5 Summary of t he opt imisat ion of cardiac out put in t he crit ically ill pat ient If hypovolaemic, replace f luids If volume overloaded, IV glyceryl t rinit rat e (GTN) and IV f urosemide

Opt imise af t erload

Sodium nit roprusside or hydralazine

Indicat ions f or inot ropes

If remains hypot ensive despit e adequat e f illing pressures: Dobut amine ⫾ dopamine f or cardiogenic shock Noradrenaline/adrenaline f or sept ic shock

Indicat ions f or IABP

Acut e mit ral regurgit at ion or VSD

Treat AF

Cont rol vent ricular response rat e Preserved LV f unct ion: ␤-blockers, verapamil, dilt iazem Impaired LV f unct ion: digoxin, amiodarone

Answ ers

Opt imise preload

SCC pp 15–20

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Respiratory System

Answ ers

Q 1.

How would you interpret a chest radiograph in a critically ill surgical patient?

A 1.

A syst em is necessary t o ensure t hat all t he appropriat e part s of a chest X-ray are review ed and not hing is missed. 䊏 䊏 䊏

䊏

䊏

䊏

䊏

Is t his t he correct pat ient ? Are t here any pot ent ially lif e t hreat ening abnormalit ies (e.g. large pneumot horax) Assess ext ernal lines and leads — Cent ral line — Endot racheal t ube (ETT) — Elect rocardiogram (ECG) — Chest drains — Pacemaker Assess t echnical aspect s — Lef t and right correct ly labelled — Cent ering of t he f ilm — Lung volumes — Penet rat ion The lungs — Pulmonary vascular pat t ern — Hila — Cost ophrenic region The mediast inum — Trachea cent ral or deviat ed — Lef t and right heart borders — Heart size The sof t t issue and bones — Fract ures — Free air under t he diaphragm SCC pp 75–76

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How would you diagnose adult respiratory distress syndrome (ARDS) in a ventilator dependent post-operative surgical patient?

A 2.

Adult respirat ory dist ress syndrome (ARDS) is part ly det ermined by t he underlying or precipit at ing condit ion. The pat hology is an increase in permeabilit y of t he alveolar capillary membrane. The diagnost ic crit eria f or ARDS are given in t he Table 2.1. Table 2.1 Diagnost ic crit eria f or ARDS Acut e onset Oxygenat ion PaO2/FIO2 ⱕ 200 CXR – bilat eral inf ilt rat es Pulmonary art ery occlusion pressure (PAOP) ⬍ 18 mmHg No clinical evidence of increasing lef t at rial pressure

Respiratory System

Q 2.

SCC pp 91–96

How is respiration controlled?

A 3.

Respirat ion is under t he cont rol of t he cent ral nervous syst em (CNS), volunt ary cont rol by t he cort ex and aut omat ic cont rol by t he medulla. Inspirat ory and expirat ory neurones in t he ret icular f ormat ion of t he medulla provide t he ‘pacemaker’ f or t he respirat ory cycle. The aim of respirat ion is t o adjust vent ilat ion t o maint ain appropriat e levels of PaO2, PaCO2 and pH. There are several mechanisms providing t he CNS w it h f eedback about t hese respirat ory paramet ers:

Answ ers

Q 3.

1. The cent ral chemorecept ors lie close t o t he f loor of t he f ourt h vent ricle and are int imat ely associat ed w it h t he respirat ory cent re. 䊏 These recept ors are sensit ive t o changes in t he pH of t he int erst it ial f luid t hat surrounds t hem 䊏 Hydrogen (H⫹) and bicarbonat e (HCO⫺ 3 ) diff use slow ly bet w een blood and t he cerebrospinal f luid (CSF), but carbon dioxide (CO2) moves f reely, allow ing rapid ref lect ion of blood CO2 in t he CSF 䊏 ↑ CO2 t ranslat es t o an exaggerat ed ↓ pH (since t he CSF has lit t le buff ering capacit y) 䊏 The pH change is det ect ed by t he cent ral chemorecept ors and st imulat es t he respirat ory cent re t o increase minut e volume

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The CO2 change in CSF is event ually buff ered by t he slow er diff usion of HCO⫺ 3 across t he blood brain barrier 2. The peripheral chemorecept ors in t he aort a and carot id bodies are sensit ive t o t he PaO2 of art erial blood and st art discharging once t he PaO2 f alls below 13 kPa (in healt hy adult s), causing an increase in t he minut e vent ilat ion. 䊏

Respiratory System

CO2 homeost asis is usually t he predominant inf luence on t he cont rol of vent ilat ion. The role of O2 becomes import ant during acut e hypoxia e.g. chest inf ect ion or pat ient s w it h CO2 ret ent ion e.g. chronic bronchit is, w ho may rely on hypoxic drive (t his, how ever represent s only t he minorit y of pat ient s w it h COPD). The eff ect s of hypercarbia and hypoxia summat e in increasing minut e volume. The cerebral cort ex is able t o exert volunt ary cont rol over brainst em aut omat ic vent ilat ion. This can be modif ied by: 䊏 䊏

Answ ers

䊏 䊏

Speech, eat ing, drinking and sleeping Sneezing, yaw ning and vomit ing Act ivit y and ant icipat ion of exercise Fever and hypot hermia

There are ot her f eedback mechanisms t o t he CNS w hich inf luence respirat ion: 䊏

䊏 䊏

M echanorecept ors – t hese occur t hroughout t he lungs and upper airw ay. The pulmonary st ret ch recept ors prot ect against overdist ent ion of t he lung in t he Hering-Breuer ref lex. Impulses are carried in t he vagus nerve t o t he CNS w hen lung volume reaches a crit ical level, prevent ing f urt her inspirat ory eff ort . Propriocept ors – t hese co-ordinat e muscular act ivit y and vent ilat ion Temperat ure recept ors – are responsible f or t he increase in respirat ory rat e w it h f ever SCC pp 60–61

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Q 4.

What is involved in initiating a breath?

A 4.

Inspirat ion is an act ive process, init iat ed by inspirat ory neurones in t he respirat ory cent re, locat ed in t he f loor of t he f ourt h vent ricle in t he brainst em. To init iat e a breat h t he respirat ory cent re st imulat es t he respirat ory muscles via t he cranial and spinal nerves.

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Answ ers

The lungs and chest w all cont ain st ret ch and mechanorecept ors, w hich signal t he inspirat ory cent re via t he vagus nerve t o end inspirat ion. The st ret ch recept ors are also responsible f or t he Hering-Breuer ref lex, w hich inhibit s f urt her inspirat ion w hen t he lung is already inf lat ed.

Respiratory System

1. The diaphragm is t he principle muscle of respirat ion, account ing f or about t hree quart ers of t he volume change. 䊏 As it cont ract s, it f lat t ens, displacing t he abdominal cont ent s f orw ard and dow nw ard. It can move up t o 7 cm on deep inspirat ion. 䊏 ↑ Int ra-t horacic volume leads t o a ↓ int ra-t horacic pressure (sub-at mospheric) 䊏 The t ranspulmonary pressure diff erence bet w een at mospheric at t he lips and t he negat ive pressure in t he alveoli drives t he air int o t he lungs during inspirat ion 2. The accessory muscles of respirat ion are responsible f or prevent ing t he collapse of t he airw ays caused by t he negat ive int ra-t horacic pressure during inspirat ion. 䊏 The ext ernal int ercost al muscles cont ract t o st abilise t he chest w all, and cont ribut e t o t he ‘bucket handle’ out er expansion of t he low er ribs, w hich f urt her increases int ra-t horacic volume 䊏 The dilat or muscles of t he upper airw ay cont ract , maint aining pat ency during inspirat ion

Expirat ion is usually a passive process of elast ic recoil. 䊏 䊏

This is f acilit at ed by t he st ored energy of t he expanded chest w all f ollow ing inspirat ion Inspirat ory neurones in t he brainst em t hen st art f iring in response t o aff erent input f rom t he st ret ch recept ors on expirat ion

Expirat ion can also be act ive e.g. f orced expirat ion during a cough, or increased airw ay resist ance. Cont ract ion of t he abdominal muscles increases int ra-abdominal pressure t hrust ing t he diaphragm int o t he t horacic cavit y. This process is enhanced by cont ract ion of t he int ernal int ercost al muscles, reducing t he capacit y of t he t horacic cavit y. Air is moved by convection from the lips to the terminal bronchioles and then by diffusion across the alveoli into the capillary network. SCC p 59

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How is respiration affected by a) exercise b) general anaesthesia c) hypovolaemia d) altitude?

A 5.

Exercise Exercise st imulat es ref lex mechanisms w hich enhance cardiorespirat ory perf ormance. Ant icipat ion of physical act ivit y by t he cort ex st imulat ed increases respirat ory cent re act ivit y. Pulmonary vent ilat ion rises f rom a rest ing value of 6–8 l/min t o values of upt o 100 l/min in t rained individuals. This increase in capacit y is mediat ed by an increase in bot h respirat ory f requency and t idal volume. Peripheral chemorecept ors play lit t le role during t his process as art erial pH, PaCO2 and PaO2 remain normal. Cardiac out put also increases upt o 30 l/min. Oxygen ext ract ion increases secondary t o met abolic acidosis produced by lact ic acid f ormat ion f rom anaerobic met abolism in t he t issues (mainly muscles). The accompanying t emperat ure rise shif t s t he oxygen dissociat ion curve t o t he right . These measures combine t o increase t he t issue oxygen consumpt ion f rom 300 ml/min at rest t o up t o 5 l/min during ext reme exercise.

Respiratory System

Q 5.

Answ ers

General anaesthesia General anaest hesia produces a dose-dependent depression of respirat ion. The overall minut e volume is reduced, mainly by a decreased t idal volume but w it h compensat ory increase in respirat ory rat e. The respirat ory pat t ern becomes almost exclusively diaphragmat ic w it h lit t le cont ribut ion f rom t he accessory muscles of respirat ion. This result s in elevat ed CO2 levels in spont aneously breat hing individuals. There is also a t endency t ow ards hypoxaemia since f unct ional residual capacit y (FRC) and hypoxic pulmonary vasoconst rict ion (HPV) are bot h reduced. The chemorecept or f eedback t o hypoxia and hypercarbia is depressed, f urt her reducing abilit y of t he CNS t o respond t o t hese changes. Hypovolaemia Loss of blood volume leads t o t issue hypoxaemia due t o hypoperf usion. The result ant met abolic acidosis secondary t o circulat ory f ailure produces a compensat ory respirat ory alkalosis by increasing t he dept h and rat e of respirat ion. Peripheral chemorecept ors in t he carot id body are direct ly st imulat ed by severe hypot ension (syst olic BP ⬍ 60 mmHg). Hypot ension cont ribut es t o increased mismat ch of vent ilat ion : perf usion

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rat ios and shunt f ormat ion, t his exacerbat es any exist ing hypoxaemia and f urt her st imulat es t he respirat ory cent re by posit ive f eedback.

䊏 䊏

䊏 䊏

SCC pp 60–65

Q 6.

What is functional residual capacity (FRC) and why is it important?

A 6.

FRC ⫽ 2.2 l: t he volume of air remaining in t he lung af t er t idal (Vt ) expirat ion. This volume of air cont inues t o t ake part in gaseous exchange at t he end of expirat ion and allow s a met hod f or cont inuous oxygenat ion t hroughout t he respirat ory cycle. It s import ance t heref ore is as an oxygen reserve, part icularly w hen vent ilat ion has st opped or is ineff icient . A capacit y is made up of t w o or more volumes. FRC is made up of residual volume (RV ⫽ 1.2 l) and expirat ory reserve volume (ERV ⫽ 1 l). RV is t he volume of air remaining in t he lung af t er a maximal expirat ion, and is t he minimum amount of air t hat can be lef t in t he lung. ERV is t he maximal volume of air t hat can be expelled af t er t idal (Vt ) expirat ion.

Answ ers

䊏

Polycyt haemia ↑ levels of 2,3-diphosphoglycerat e (2,3-DPG) (causes right shif t of ODC) Increased HPV (↑ pulmonary art ery pressures) Increased mit ochondrial densit y Increased maximum vent ilat ory capacit y

Respiratory System

Altitude High alt it ude decreases baromet ric pressure, w hich in t urn reduces t he inspired oxygen part ial pressure. This is a f orm of hypoxic hypoxaemia, and has a similar eff ect t o breat hing oxygen of low (⬍21% ) concent rat ion. The physiological changes t hat t ake place in order t o adapt t o t hese condit ions is t ermed acclimat isat ion. Art erial hypoxaemia is det ect ed by t he peripheral chemorecept ors, w hich st imulat e t he respirat ory cent re. Alveolar vent ilat ion can increase f ivef old t o levels above 20 l/min, reducing t he PaCO2 level by upt o 80% . People living at high alt it ude have ot her ‘adapt ed’ physiological changes:

Closing capacit y (CC): t his is t he lung volume w here small airw ays begin t o collapse on expirat ion. Normally CC is great er t han FRC.

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How ever, if CC is less t han FRC t hen t here w ill be airw ay closure, leading t o collapse during t idal (quiet ) vent ilat ion, result ing in art erial hypoxaemia. Thus, any f act or t hat decreases FRC w ill increase t he risk of airw ay closure and collapse (Table 2.2).

Respiratory System

Table 2.2 Fact ors aff ect ing FRC Fact ors increasing FRC

Fact ors decreasing FRC

PEEP/CPAP

Ext remes of age (very young and old)

Obst ruct ive airw ays disease e.g. ast hma, emphysema

Supine post ure Anaest hesia Obesit y Abdominal/Thoracic surgery* Pulmonary disease e.g. oedema or f ibrosis

* The eff ect s of surgery on lung volume can last f or up t o 2 w eeks, causing: ↓ Vit al capacit y (VC) by 45% and ↓ FRC by 25% These eff ect s are seen most signif icant ly in upper abdominal and t horacic operat ions.

SCC pp 65–67 Answ ers

Q 7.

What is measured using a spirometer?

A 7.

Lung volumes can be measured direct ly by spiromet ry and vary depending on age, sex, and size (height being a closer correlat e t han w eight ) (Fig. 2.1). Definitions: 䊏

Tot al lung capacit y (TLC ⫽ 4.2–6 l): t his is t he volume of air in t he lungs at t he end of a maximal inspirat ion. TLC ⫽ IRV ⫹ ERV ⫹ Vt ⫹ RV ⫽ VC ⫹ RV

䊏 䊏

䊏 䊏

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Tidal volume (Vt ⫽ 0.5 l): t his is t he volume of air inspired and expired during quiet breat hing. Inspirat ory reserve volume (IRV ⫽ 1.9–3.3 l): t his is t he maximal volume of air t hat can be inspired above t idal (Vt ) inspirat ion. ERV ⫽ 0.7–1 l: t his is t he maximal volume of air t hat can be expelled af t er t idal (Vt ) expirat ion. VC ⫽ 3.1–4.8 l: t his is t he maximal volume of air t hat can be expired f ollow ing a maximal inspirat ion i.e. Vt ⫹ IRV ⫹ ERV. SCC pp 61–67

Key Quest ions in Surgical Crit ical Care

6.0

Inspirat ory reserve volume

Inspirat ory capacit y

Volume

Expirat ory reserve volume

Tot al lung capacit y Funct ional residual capacit y

Respiratory System

Vit al capacit y

Tidal volume

Residual volume 0

Fig. 2.1 Spiromet er t race of lung volumes (Source: Pinnock, Lin and Smit h (Eds): Fundament als of Anaest hesia (1st Ed): GM M Lt d. London, 1999, p 413).

What dynamic tests of respiratory function do you know?

A 8.

Test s of dynamic lung perf ormance assess f orced expirat ion, and are measured w it h a spiromet er.

Answ ers

Q 8.

Uses: 䊏 䊏 䊏 䊏

Aid diagnosis Quant if y pulmonary impairment M onit or t he disease process M onit or t he response t o t herapy

Forced expiration 䊏

䊏

Forced vit al capacit y (FVC) – t his is t he volume of gas t hat can be f orcibly expired af t er a maximal inspirat ion. This volume is of t en less t han t hat achieved by measurement f rom slow expirat ion, due t o compression of t he int ra-t horacic airw ays. Forced expirat ory volume (FEV1) – t his is t he volume of t he vit al capacit y breat h expired in t he f irst second.

The FEV1/FVC rat io can be used t o help dist inguish obst ruct ive f rom rest rict ive limit at ion t o expired airf low. Normally t he FEV1/FVC rat io is 0.8–0.9.

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7

6

Expired volume (I)

Respiratory System

5 FVC 4 FEV 3

2

1

0 0

1

2

3

4

5

6

Time (s)

Answ ers

Fig. 2.2 Lung f unct ion t est s (Source: Pinnock, Lin and Smit h (Eds): Fundament als of Anaest hesia (1st Ed): GM M Lt d. London, 1999, p 415).

1. In rest rict ive condit ions bot h t he FEV1 and FVC are reduced but t he rat io is t ypically normal or increased e.g. pulmonary condit ions such as f ibrosis or chest w all rest rict ions such as kyphoscoliosis or f lail chest . This is because t he vit al capacit y is ‘rest rict ed’ i.e. reduced t o a larger degree t han obst ruct ive and t he limit at ion is overall VC rat her t han t he t ime t aken t o expel t his volume. 2. In obst ruct ive condit ions t he FEV1 is reduced t o a f ar great er degree t han t he FVC, hence t he rat io is much low er e.g. ast hma, emphysema or any cause of obst ruct ion such as f oreign object or paralysis of t he vocal cords. In t his case t he VC is less reduced but is ‘obst ruct ed’ f rom being expelled by t he narrow ed airw ays (Table 2.3). Table 2.3 The variat ion in dynamic lung f unct ion t est s in obst ruct ive and rest rict ive condit ions

Rest rict ive Obst ruct ive

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FEV 1

FVC

Rat io

↓↓ ↓↓↓

↓↓ ↓

Normal or ↑ ↓

Key Quest ions in Surgical Crit ical Care

Peak expiratory flow rate (PEFR) This is used in obst ruct ive airw ay condit ions t o assess t reat ment eff ect s and reversibilit y. It is measured w it h a peak f low met er (t he best of at least t hree at t empt s is t he value recorded).

䊏 䊏 䊏 䊏 䊏

Ast hma COPD Upper airw ay obst ruct ion Tracheal st enosis Poor expirat ory eff ort e.g. musculoskelet al problems aff ect ing t he chest w all SCC pp 61–67

What is meant by respiratory compliance?

A 9.

Compliance is t he change in volume caused by a unit change in pressure: Compliance =

change in volume L change in pressure kPa

Answ ers

Q 9.

Respiratory System

PEFR is reduced w it h:

This measurement gives an indicat ion of dist ensabilit y of t he lungs, and t heref ore t he amount of w ork needed t o expand t hem during inspirat ion. Compliance curves f orm a charact erist ic sigmoid-shape w it h increasing pressure (Fig. 2.3). The slope of t he line gives t he measure of compliance. The st eeper t he slope of t his line t he great er t he compliance, so less pressure is required t o produce a unit rise in volume or alt ernat ively more volume can be inspired f or unit change in pressure. Respirat ory compliance consist s of chest w all and lung compliance. The t endency of t he lungs t o collapse by elast ic recoil is count ered by t he t endency of t he t horacic cage (chest w all) t o expand out w ards. The normal rest ing lung volume (FRC) is t he equilibrium bet w een t hese t w o opposing f orces. Bot h lung and chest w all compliance are 200 ml/cmH2O. Tot al respirat ory compliance is a sum of t he reciprocal of t hese t w o values and is usually about 100 ml/cmH2O.

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100 Chest w all

Respiratory System

Vit al capacit y (% )

Respirat ory syst em

FRC Lung 0 ⫺2

0

⫹2

Int rapulmonary pressure (kPa)

Fig. 2.3 Lung and chest w all compliance (Source: Pinnock, Lin and Smit h (Eds) Fundament als of Anaest hesia (1st Ed): GM M Lt d. London, 1999, p 417).

Fact ors decreasing compliance: Answ ers

䊏

䊏 䊏 䊏 䊏 䊏 䊏 䊏

Ext remes of lung volume (at low lung volumes t here is collapse of small airw ays and alveoli and at high lung volumes t he elast ic f ibres of t he lung are f ully st ret ched and large pressures are required t o f urt her increase volume) Ext remes of age Supine post ure Pregnancy (because of diaphragmat ic splint ing) ARDS Pulmonary oedema/f ibrosis Ankalosing spondylit is Kyphoscoliosis

Vent ilat ion of pat ient s w it h decreased lung compliance leads t o large increases in airw ay pressure per unit change in volume. This risks barot rauma, damaging t he lungs and f urt her reducing t he compliance. Dynamic compliance is measured during gas f low and f orms a charact erist ic loop. This is caused by t he increased eff ort needed during inspirat ion t o overcome t he elast ic f orces resist ing lung expansion. Normal expirat ion is a passive process driven by t he st ored energy f rom inspirat ion. The diff erence bet w een t he curves is t ermed hyst eresis (Fig. 2.4). SCC pp 62–64 180

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50

0 ⫹0.5

FRC

0

⫺0.5

⫺1.0

⫺1.5

Respiratory System

Lung volume (% )

100

Int rapleural pressure (kPa)

Fig. 2.4 Compliance during spont aneous vent ilat ion (Source: Pinnock, Lin and Smit h (Eds): Fundament als of Anaest hesia (1st Ed): GM M Lt d. London, 1999, p 419).

Answ ers

Q 10. How do ventilation and perfusion vary with spontaneous and mechanical ventilation? What do you understand by the terms ‘shunt’ and ‘dead space’? A 10. Dist ribut ion of vent ilat ion is uneven during t he respirat ory cycle. During spont aneous respirat ion, t he majorit y of inspired gas passes t o t he low er (dependent ) part s of t he lung. This is because t here is more negat ive pressure generat ed at t he base t han at t he apex, f avouring great er expansion. Blood f low is also great er at t he base of t he lung, ow ing t o t he increased hydrost at ic pressure. Thus during spont aneous respirat ion t here is good mat ching of vent ilat ion (V) and perf usion (Q). Vent ilat ion increases at a slow er rat e t o perf usion dow n t he lung, w it h t he best mat ching of V/Q at t he level of t he 3rd t o 4t h ribs. M at ching of vent ilat ion t o perf usion prevent s t he development of hypoxaemia, w hich may result f rom: 䊏 䊏

Shunt – perf used areas w it h inadequat e vent ilat ion Dead space – vent ilat ed areas w it h inadequat e perf usion

The sit uat ion is reversed during mechanical (posit ive pressure) vent ilat ion w here pref erent ial vent ilat ion t ends t ow ards t he upper (non-dependent ) areas of t he lung. This decreases t he

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dependent lung volume and increases V/Q mismat ch, leading t o art erial hypoxaemia.

Respiratory System

The lung has a mechanism w hereby it can improve mat ching of V/Q by divert ing blood aw ay f rom area w it h poor vent ilat ion. This is t ermed as HPV and result s in decreasing t he amount of shunt ed blood, t hereby improving art erial hypoxaemia. 䊏 䊏

Hypoxaemia t hat occurs as a result of shunt cannot be improved by increasing t he oxygen concent rat ion. General anaest het ics oblit erat e HPV and t his is one reason w hy supplement al oxygen is required in pat ient s during and af t er anaest hesia. SCC p 65

Q 11. How would you go about interpreting arterial blood gas (ABG) analysis? A 11. Normal values: Answ ers

pH PCO2 PO2 SBC/HCO3 ABE/SBE SAT

7.35–7.45 4.4–5.8 kPa (33–44 mmHg) 10.0–13.3 kPa (75–100 mmHg) 20–30 mmol/l ⫺2.5 t o ⫹2.5 mmol/l 95–98 %

Check individual depart ment al values f or normal range.

Def init ion of t erms used: pH – Negat ive logarit hm (base10) of t he H⫹ cont ent in blood. The pH is inversely proport ional t o t he blood H⫹ concent rat ion; t heref ore, as pH decreases so H⫹ concent rat ion rises, f or example: pH

H⫹ concent rat ion (nmol/l)

7.0 7.2 7.4 7.6

100 63 40 25

St andard bicarbonat e (SBC) – It is t he measure of plasma bicarbonat e correct ed t o a PCO2 of 5.3 kPa, removing t he inf luence of respirat ory eff ect s on pH. 182

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Key Quest ions in Surgical Crit ical Care

Act ual base excess (ABE) – It is an in vit ro measurement of met abolic acidosis (⫺ve) or alkalosis (⫹ve). PCO2 is correct ed t o 5.3 kPa, t heref ore t his represent s t he non-respirat ory component s only.

Temperat ure has a signif icant eff ect on t he result s of art erial blood gas (ABG) analysis. 䊏 䊏

Decreasing t emperat ure decreases pH (normal pH at 27⬚C is 7.25) Decreasing t emperat ure decreases PO2

Respiratory System

St andard base excess (SBE) – It is an in vivo assessment of acid-base balance since it adjust s f or t he buff ering of haemoglobin and plasma prot eins in w hole blood compared w it h int erst it ial f luid.

Theref ore:

Acid-base dist urbances: Acidosis Alkalosis

Answ ers

1. It is essent ial t o key t he correct body t emperat ure int o t he blood gas analyser w hen processing samples 2. Samples should be analysed as soon as possible af t er t hey have been t aken t o improve t he accuracy of t he result s

pH ⬍ 7.35 pH ⬎ 7.45

Primary change in PaCO2 is respirat ory Primary change in HCO⫺ 3 is met abolic (non-respirat ory)

These changes can eit her be: 䊏 䊏 䊏

Uncompensat ed – The pH def icit remains uncorrect ed Part ially compensat ed – The pH is ret urned t ow ards normal Fully compensat ed – The pH is ret urned t o normal

Overcorrect ion is not usually possible; t heref ore a pat ient w it h met abolic acidosis cannot become alkalot ic by compensat ion unless t here is a compounding f act or present t o account f or it e.g. mechanical vent ilat ion. Int erpret at ion of result s: 䊏 䊏 䊏

Vivas

Look at t he pH – Is t his alkalosis or acidosis? Look at t he PCO2 – Is t his primarily respirat ory? Look at t he SBC – Is t his primarily met abolic?

Key Quest ions in Surgical Crit ical Care

183

The primary dist urbance is t hat w hich explains t he observed pH. 䊏 䊏

Respiratory System

Look at t he base excess is t here compensat ion? Ot her inf ormat ion obt ained f rom t he ABG analysis can give f urt her clues: — Is t here anaemia? — Is t here hypoxaemia? — Is t here hyperglycaemia? — Is t he lact at e elevat ed?

There are of t en ot her clues f rom t he hist ory and clinical examinat ion. There may be a mixed pict ure of respirat ory and met abolic compromise, compounding t he eff ect s of t he original def icit . SCC pp 66–75

Q 12. How would you classify hypoxia? A 12. Hypoxia is reduced oxygen delivery t o t he t issues of t he body: Answ ers

DO2 ⫽ CO % [(Hb %

Sat

/100 % 1.34) ⫹ (PaO2 % 0.003)]

w here, DO2 is t he oxygen delivery; CO is t he cardiac out put ; Hb % Sat /100 % 1.34 represent s t he amount of oxygen carried by haemoglobin in t he blood (1.34 is a calculat ion const ant ); PaO2 % 0.003 represent s t he amount of oxygen dissolved in blood, and is usually negligible compared t o t hat combined w it h haemoglobin. There are several t ypes of hypoxia depending on w here t he reduct ion in oxygen delivery occurs. Hypoxic hypoxia This result s in ↓ Sat and ↓ PaO2 and is caused by: 䊏 䊏

䊏 䊏 䊏

184

Vivas

Low oxygen concent rat ion of t he inspired gas mixt ure e.g. at alt it ude Hypovent ilat ion e.g. at elect asis and airw ay collapse, airw ay obst ruct ion, drugs (opioids and anaest het ic agent s), cent ral depression of vent ilat ion Diff usion f ailure bet w een t he alveolus and capillary e.g. pulmonary oedema and f ibrosis or pneumonia Vent ilat ion/perf usion imbalance e.g. ARDS Shunt ing of blood f rom t he venous t o art erial circulat ion e.g. cyanot ic heart disease

Key Quest ions in Surgical Crit ical Care

Anaemic hypoxia This is t he result of low Hb w hich may be caused by: 䊏

䊏 䊏

At rest , anaemic hypoxia is not usually a problem, unless t he pat ient has co-exist ing ischaemic heart disease. During exercise, t here can be severe limit at ion. St agnant hypoxia This is due t o a low cardiac out put and causes high oxygen ext ract ion leading t o low er venous oxygen cont ent . There is also decreased removal of w ast e product s of met abolism leading t o t he accumulat ion of lact at e (met abolic acidosis).

SCC pp 76–78

Answ ers

Hist ot oxic hypoxia Here t he delivery of oxygen t o t he t issues is adequat e but t hey are unable t o ut ilise it e.g. cyanide poisoning.

Respiratory System

䊏

↓ Red blood corpuscle (RBC) f rom ↓ product ion, blood loss or ↑ dest ruct ion ↓ Hb per RBC e.g. hypochromic anaemia of iron def iciency Abnormal f orms of Hb e.g. sickle cell disease Reduced binding of oxygen t o Hb e.g. carbon monoxide poisoning

Q 13. Which patients are at risk of post-operative hypoxaemia? What methods are available to deliver oxygen to a spontaneously breathing patient after surgery? A 13. Hypoxaemia can occur w it h any pat ient af t er surgery. Some groups of pat ient s are at higher risk, and should receive prolonged oxygen t herapy (at least 72 hours): 䊏 䊏 䊏 䊏 䊏 䊏 䊏 䊏

Vivas

Ischaemic heart disease Anaemia M ajor abdominal (esp. upper gast roint est inal t ract (GIT)) and t horacic operat ions Hypot ension/low CO (it is import ant t o t reat t he cause) Hypot hermia Obese pat ient s t hese have an increased oxygen Hypert hermia/sepsis demand Shivering

}

Key Quest ions in Surgical Crit ical Care

185

Respiratory System

Variable performance oxygen delivery systems The oxygen concent rat ion delivered t o t he pat ient is not const ant and depends on t he minut e volume (M V), or more specif ically t he peak inspirat ory f low rat e (PIFR). As t he PIFR increases more air w ill be ent rained f rom t he surroundings and t he oxygen concent rat ion delivered t o t he pat ient w ill decrease, unless t he oxygen f low rat e is increased. The f ollow ing are t w o examples of syst ems commonly used af t er surgery (Table 2.4): Table 2.4 The diff erent syst ems f or delivering variable concent rat ions of oxygen Hudson mask O2 f low (l/min) 2 4 6 8 10

Nasal specs

O2 conc. (% )

O2 f low (l/min)

O2 conc. (% )

24–38 35–45 51–61 57–67 61–73

1 2 4

25–29 29–35 32–39

Answ ers

Fixed-performance oxygen delivery systems (Venturi masks) These deliver a const ant oxygen concent rat ion independent of t he pat ient ’s respirat ory pat t ern (M V and PIFR). The oxygen supply ent rains air at a f ixed rat e via a jet built int o t he mask. The t ot al f low rat e is t heref ore higher t han t he PIFR and dilut ion of t he oxygen supply does not occur. The jet ent rainment devices are coloured coded and higher f low rat es must be dialled w hen increased oxygen concent rat ions are required (Table 2.5). Table 2.5 The syst em f or delivering a know n concent rat ion of oxygen Colour code Whit e Yellow Red Green

O2 supply f low rat e (l/min)

Delivered O2 conc. (% )

4 8 10 15

28 35 40 60 SCC pp 76–78

186

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Key Quest ions in Surgical Crit ical Care

Q 14. How would you classify respiratory failure, and what are the signs?

Type I: ↓ PaO2 w it h normal or ↓ PaCO2 (t here may be respirat ory alkalosis) 䊏 䊏 䊏 䊏 䊏

Pulmonary embolism Fibrosing alveolit is Pneumonia w hen severe, t hese condit ions may be Ast hma Early ARDS associat ed w it h Type II f ailure

Respiratory System

A 14. Respirat ory f ailure occurs w hen t he PaO2 and PaCO2 can no longer be maint ained w it hin normal limit s. If unt reat ed t his leads on t o cellular hypoxaemia and acidosis by decreasing t he capacit y f or gaseous exchange. Respirat ory f ailure may be split up int o t w o t ypes, depending on t he CO2 concent rat ion present in blood. Pat ient s may progress f rom one t ype t o t he ot her:

}

Type II: Vent ilat ory Failure

䊏 䊏 䊏 䊏 䊏 䊏 䊏

M echanical obst ruct ion t o t he airw ay e.g. vomit , blood, f oreign body or t umour Obst ruct ive airw ays disease e.g. COPD, severe ast hma Advanced ARDS Severe pneumonia Neuromuscular disorders e.g. cervical cord injury, polio, Guillain Barré, mot or neurone disease Chest w all def ormit ies e.g. chest t rauma (f lail chest ), ankalosing spondylit is, kyphoscoliosis Cent ral depression of respirat ory drive e.g. drugs (especially sedat ives), head injury, brain t umours

Answ ers

↓ PaO2 w it h ↑ PaCO2 (respirat ory acidosis)

Signs of respiratory failure 䊏 䊏 䊏 䊏

Vivas

Tachypnoea Dyspnoea Tachycardia The use of accessory muscles of respirat ion — int ercost al recession — subcost al recession — t racheal t ug

Key Quest ions in Surgical Crit ical Care

187

䊏 䊏 䊏

Respiratory System

Inabilit y t o speak in sent ences (leading on t o t ot al inabilit y t o speak) Impaired consciousness (t his is a grave sign) Cyanosis is a blue/purple discolourat ion of t he skin caused by t he presence of deoxyhaemoglobin (in amount s ⬎5 g/dl). This is a not oriously unreliable sign, part icularly in areas w it h poor or art if icial light ing. It is possible t o observe: — Cyanosis w it hout hypoxia (polycyt haemia) — Hypoxia w it hout cyanosis (anaemia) SCC pp 79–80

Q 15. What are the indications for intubation and mechanical ventilation? A 15. Posit ive pressure vent ilat ion may be required f or signs of respirat ory f ailure. The decision w het her t o inst it ut e vent ilat ory support should be t aken by a senior clinician, and is based on several f act ors, including: 䊏

Answ ers

䊏

The pre-morbid healt h st at us of t he pat ient is an import ant index of survivabilit y f ollow ing admission t o t he int ensive care unit (ICU). There should be pot ent ial reversibilit y of t he admit t ing condit ion.

Indications for mechanical ventilation Inadequat e vent ilat ion: 䊏 䊏 䊏 䊏 䊏

Apnoea RR ⬎ 35/min VC ⬍ 15 ml/kg TV ⬍ 5 ml/kg PaCO2 ⬎ 8 kPa

(Normal range is 12–20/min f or adult s) (Normal range is 65–75 ml/kg) (Normal range is 5–7 ml/kg) (This depends on t he pat ient s normal PaCO2)

Inadequat e oxygenat ion: 䊏

PaO2 ⬍ 8 kPa

(Breat hing ⬎ 60% oxygen)

Specif ic surgical indicat ions: Head injury – If t his result s in an unprot ect ed airw ay, t here is an increased risk of gast ric aspirat ion w it h t he development of chemical pneumonit is. Ot her indicat ions are a low ered Glasgow coma score (GCS) (t his is usually t aken as below 8) or if t here are sympt oms and signs of raised int racranial pressure (in order t o cont rol t he PaCO2). 188

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Key Quest ions in Surgical Crit ical Care

Facial t rauma – Bleeding int o t he airw ay makes breat hing laboured and may obst ruct t he airw ay complet ely. Sw allow ed blood is ext remely emet ogenic and may lead t o aspirat ion of st omach cont ent s. There may be disrupt ion of t he airw ay archit ect ure result ing in part ial or complet e airw ay compromise. There may also be an associat ed head injury (or neck injury).

Answ ers

High spinal injury – Pat ient s w it h injuries t o t he spinal cord below t he level of C5 may have relat ively lit t le in t he w ay of respirat ory compromise, as t he diaphragm cont inues t o provide much of t he inspirat ory excursion required. Above t his, how ever t here w ill be respirat ory diff icult ies since t he phrenic nerve arises f rom C3, 4, 5. There may also be pot ent ial respirat ory compromise f rom gast ric aspirat ion, or any associat ed head injury or f acial t rauma described above.

Respiratory System

Chest injury – This may be required w it h a f lail chest , t he dyskinet ic segment cont ribut ing lit t le t o t he eff iciency of vent ilat ion. There may be a pneumot horax, w hich should be drained prior t o int ubat ion and posit ive pressure vent ilat ion. Undrained pneumot horaces have t he pot ent ial t o t amponade w it h int ermit t ent posit ive pressure vent ilat ion (IPPV). The presence of a pulmonary cont usion may reduce t he eff iciency of gas exchange and require vent ilat ion.

Burns – Circumf erent ial burns t o t he neck or t he chest need prompt int ubat ion and vent ilat ion since severe respirat ory compromise can occur. The airw ay may be obst ruct ed and respirat ory excursion may be severely limit ed, requiring simult aneous escharot omy. Smoke or st eam inhalat ion requires int ubat ion as soon as possible t o prevent subsequent airw ay compromise. The only signs may be t he presence of soot on t he nose or mout h. The t rachea should be int ubat ed in t he f ollow ing circumst ances: 䊏 䊏 䊏

Risk of gast ric aspirat ion in t he unprot ect ed airw ay (t o prot ect t he low er airw ay) Upper airw ay obst ruct ion To f acilit at e t he use of posit ive pressure vent ilat ion SCC pp 80–87

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Key Quest ions in Surgical Crit ical Care

189

Q 16. What are the effects of mechanical ventilation?

Respiratory System

A 16. The principle f or gas f low w it h IPPV is t he same as f or spont aneous vent ilat ion. Gas f low s dow n a pressure gradient f rom t he mout h t o t he alveoli. The diff erence, how ever, lies in t hat t he proximal driving pressure is posit ive rat her t han at mospheric, and t he dist al pressure is zero rat her t han negat ive. Work is st ill done t o expand t he lung and chest w all and t his is st ored and used t o drive expirat ion, w hich is passive. IPPV eff ect s many body syst ems: Respirat ory 䊏

䊏 䊏

Answ ers 䊏

FRC is recovered, improving t he eff iciency of vent ilat ion. The inspired oxygen concent rat ion can be adjust ed t o opt imise oxygenat ion, and CO2 removal is improved in pat ient s w it h respirat ory f ailure. Lung w at er can be reduced, f urt her improving oxygenat ion The high pressures somet imes needed t o expand t he lung can cause damage due t o barot rauma, leading t o pneumot horax f ormat ion. This is especially t rue w hen t he respirat ory compliance is reduced e.g. w it h ARDS. Subsequent vent ilat ion w it h drained pneumot horaces can be diff icult and ineff icient , due t o air leaks. Reduct ion of HPV, w it h result ant increased mismat ching of vent ilat ion

Cardiovascular There is an overall reduct ion in BP and CO: 䊏 䊏

䊏 䊏

Reduced pre-load (↓ venous ret urn t o t he right vent ricle) due t o loss of negat ive pressure int ra-t horacic pump Increased pulmonary vascular resist ance (PVR) – t his leads init ially t o right vent ricular dilat at ion result ing in inadequat e lef t vent ricular f illing (because of volume increase in RV) Sedat ion reduces t he art erial BP Correct ion of hypoxia, hypercarbia and acidosis decreases endogenous cat echolamine drive on t he cardiovascular syst em (CVS)

Renal 䊏

190

Vivas

Decreased cardiac out put result s in: — ↓ Renal blood f low — ↓ Renal perf usion pressure

Key Quest ions in Surgical Crit ical Care

— ↓ Glomerular f ilt rat ion rat e — ↓ Urine out put Cerebral

䊏

Increased int ra-t horacic pressure is t ransmit t ed t hrough t he venous syst em t o ↑ int ra-cranial pressure (ICP) Conversely reduct ion of CO2 by vent ilat ion reduces cerebral blood volume t hereby ↓ ICP

M et abolic 䊏

Tit rat ion of PaCO2 can be used t o compensat e f or acid-base dist urbances SCC pp 80–87

Respiratory System

䊏

Q 17. What modes of mechanical ventilation do you know? Which of these modes are used for weaning? A 17. Controlled mandatory ventilation (CMV)

䊏 䊏

䊏

The vent ilat or w ill deliver a set t idal volume (Vt ) at a set respirat ory rat e (RR) No inspirat ory eff ort is made by t he pat ient Any at t empt t o breat he or cough by t he pat ient during inspirat ion can result in dangerously high peak airw ay pressures (PAWP), leading t o barot rauma The pat ient must be deeply sedat ed and is of t en paralysed

Answ ers

䊏

Synchronised intermittent mandatory ventilation (SIMV) 䊏

䊏

䊏

The minut e volume is composed of a mixt ure of mandat ory Vt breat hs (init iat ed by t he vent ilat or) and some spont aneous breat hs (init iat ed by t he pat ient ) There is co-ordinat ion (synchronisat ion) bet w een t he vent ilat or-init iat ed breat hs and t he pat ient -init iat ed breat hs, so t hat bot h are not delivered simult aneously. This prevent s t he high PAWP somet imes seen w it h CM V The pat ient s may be less deeply sedat ed and muscle paralysis is rarely required

SIM V has a number of advant ages over CM V: 䊏 䊏

Vivas

↓ level of sedat ion required ↓ incidence of ↑ PAWP (hence ↓ incidence of barot rauma)

Key Quest ions in Surgical Crit ical Care

191

䊏 䊏 䊏

Respiratory System

䊏

↓ mean airw ay pressure (M AWP) ⇒ less ↓ in CO and BP (great er haemodynamic st abilit y) Bet t er mat ching of vent ilat ion and perf usion Easier assessment of spont aneous breat hing act ivit y Improved w eaning f rom vent ilat ion (less disuse at rophy of t he respirat ory muscles since spont aneous vent ilat ion is not discouraged)

Pressure control ventilation (PCV) CM V and SIM V are examples of volume-cont rolled vent ilat ion, w here a pre-set volume is delivered t o t he pat ient . PCV diff ers in t hat t he pressure is set and t he volume delivered t o t he pat ient w ill vary depending on t he compliance (see previous sect ion) of t he lungs and t he inspirat ory t ime. 䊏 䊏 䊏

Answ ers

䊏 䊏 䊏

Pat ient s w it h ↓ lung compliance w ill receive a ↓ Vt f or any set pressure Square w ave pressure t race M AWP is higher f or any level of PAWP — ↑ M AWP equat es w it h ↑ oxygenat ion ↓ PAWP ⇒ ↓ risk of barot rauma RR set on vent ilat or St art w it h pressure of 30 cmH2O t o give Vt of 10–12 ml/kg (depends on lung compliance)

Pressure support ventilation (PSV) This is somet imes ref erred t o as pressure assist ed vent ilat ion: 䊏 䊏 䊏 䊏

The pat ient t riggers t he vent ilat or t o deliver a pre-set pressure t o t he lungs RR det ermined by t he pat ient Vt depends on t he level of pressure support (PS) and t he lung compliance Set level of PS t o give Vt of 10–12 ml/kg (usually 15–30 cmH2O)

This mode of vent ilat ion can be used in isolat ion or in conjunct ion w it h PCV or SIM V. It s main use is f or w eaning f rom vent ilat ion, w it h t he level of PS reduced as t he mechanics of respirat ion improve: 䊏 䊏

192

Vivas

M inimal sedat ion needed (only t o t olerat e t he ETT). Has t he advant age of maint aining muscular act ivit y, t hereby minimising t he risks of disuse at rophy.

Key Quest ions in Surgical Crit ical Care

SCC pp 80–87

Respiratory System

SIM V and PSV are t he main w eaning modes. SIM V diff ers in t hat t he vent ilat or w ill alw ays give some mandat ory breat hs, w it h spont aneous breat hs being ‘t riggered’ by t he pat ient . PSV has no mandat ory breat hs and ‘pat ient -t riggered’ breat hs makes up t he ent ire minut e volume. Wit h bot h of t hese modes any inspirat ory eff ort by t he pat ient (t riggering), is sensed and t he vent ilat or is inst ruct ed t o assist t he breat h. As w eaning progresses, t he level of inspirat ory eff ort required t o t rigger an assist ed breat h is increased and t he level of support is decreased, increasing t he pat ient ’s cont ribut ion unt il t hey are event ually able t o breat he unaided.

Q 18. Why is it important to maintain adequate lung volume? What methods do you know for optimising lung volume? Answ ers

A 18. M anoeuvres designed t o opt imise lung volume aim t o increase FRC by alveolar recruit ment , re-expanding collapsed areas of t he lung. This places t he lung on a more eff icient (st eeper) part of t he compliance curve, generat ing maximum volume change per unit increase in pressure. M aint aining lung volume prevent s airw ay collapse and alveolar at elect asis, t hus minimising shunt and reducing t he eff ect ive dead space per breat h. This reduces t he w ork of breat hing and opt imises art erial oxygenat ion f or any given inspired oxygen concent rat ion (FIO2). The FIO2 should be set at a level t hat is as low as possible t o prevent hypoxaemia. The proport ion of nit rogen in t he lungs is import ant since t his inert gas does not t ake part in gaseous exchange. Oxygen is readily absorbed f rom t he alveoli int o t he capillary net w ork leading t o absorpt ion at elect asis. A higher FIO2 reduces t he rat io of nit rogen t o oxygen, increasing t his t endency t o collapse. The f ollow ing met hods may be employed t o opt imise lung volume: 䊏 䊏

Vivas

Cont inuous posit ive airw ays pressure (CPAP) is used during spont aneous vent ilat ion Posit ive end expirat ory pressure (PEEP) is used during vent ilat or delivered breat hs

Key Quest ions in Surgical Crit ical Care

193

Respiratory System

Typically 5–10 cmH2O is used. M ore may be used w it h mechanical vent ilat ion and pat ient s w it h uncompliant lungs e.g. ARDS may require upt o 15 cmH2O of PEEP. Bot h t hese met hods increase t he risk of barot rauma and volut rauma and should be used w it h caut ion in ast hmat ic pat ient s (risk of ext remely high airw ay pressures). 䊏

Inverse rat io vent ilat ion (IRV). The usual I:E rat io of 1:2 gives adequat e t ime f or expirat ion, w hich is passive. Reversing t he rat io t o 1:1, 2:1 or 3:1 w ill progressively decrease t he t ime f or expirat ion, w hich w ill generat e AUTOPEEP. This increases t he M AWP w it hout increasing t he PAWP. This improves oxygenat ion, w it hout any increased risk of barot rauma. IRV requires deep sedat ion and paralysis since it is a very unnat ural and uncomf ort able mode of vent ilat ion.

Associat ed eff ect s of t hese manoeuvres t o opt imise lung volume: 䊏

Answ ers

䊏 䊏

The increased int ra-t horacic pressure is t ransmit t ed via t he venous syst em t o t he CNS, increasing ICP The increased int ra-t horacic pressure reduces venous ret urn low ering CO and BP CO2 eliminat ion is reduced result ing in respirat ory acidosis SCC pp 80–87

Q 19. What factors affect the ability to wean from mechanical ventilation? A 19. The ‘w eaning’ process is re-inst it ut ion of independent spont aneous respirat ion af t er a period of vent ilat ory support . The w it hdraw al of art if icial vent ilat ion is achieved gradually and success depends on several f act ors: Durat ion of mechanical vent ilat ion – The w eaning process is quicker w it h post -operat ive cases (⬍24 hours vent ilat ed). Past medical hist ory – Respirat ory and cardiovascular disease can pose a signif icant hurdle t o rapid successf ul w eaning. Current medical problems – Act ive chest inf ect ion, signif icant areas of collapse or consolidat ion, and heart f ailure great ly decrease t he chances of success. These condit ions are relat ive cont ra-indicat ions t o act ive w eaning. Nut rit ional st at e and muscle pow er 194

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Key Quest ions in Surgical Crit ical Care

Drugs – Residual levels of opioids, sedatives and muscle relaxants will determine the effectiveness and speed of the weaning process. Signs of f ailure during w eaning 䊏 䊏 䊏

Tachypnoea and dyspnoea Hypoxia and hypercarbia Use of accessory muscles of respirat ion Exhaust ion and f at igue leading t o reduced conscious level

Weaning pre-condit ions 䊏 䊏 䊏 䊏 䊏

Pract ical aspect s of w eaning f rom vent ilat ory support 䊏 䊏 䊏 䊏 䊏 䊏

Weaning plan should be st art ed as early as possible in t he day – ideally af t er t he morning w ard round M inimise sedat ion and opioid analgesia – how ever bear in mind t hat pain increases oxygen demand and risk of f ailure Decrease mandat ory respirat ory rat e delivered by t he vent ilat or – gradually t ow ards zero Decrease t he pressure support level – maint aining adequat e Vt Decrease PEEP When: SIM V rat e ⫽ 0 PS ⫽ 10 cmH2O PEEP ⫽ 5 cmH2O

Answ ers

䊏

St art s only af t er recovery f rom t he pat hology t hat required vent ilat ory support Haemodynamic st abilit y Opt imisat ion of oxygen delivery t o t he t issues – Hb and cardiac out put Opt imisat ion of nut rit ional st at us t o prevent muscle f at igue Act ive sepsis and pyrexia should be excluded since t hese increase oxygen demand and may lead t o early f ailure FIO2 should be ⬍0.6

Respiratory System

䊏

Then t he pat ient may be put on a T-piece (⫾ CPAP of 5 cmH2O) f or a f ew hours at a t ime, alt ernat ing w it h PS via t he vent ilat or. Good clinical and ABG monit oring is required unt il t he pat ient is able t o maint ain adequat e vent ilat ion independent ly. This process may t ake w eeks t o complet e. There is current ly no reliable predict or of successf ul w eaning. SCC pp 80–87

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Key Quest ions in Surgical Crit ical Care

195

Q 20. What are the causes of airway obstruction? How may these be managed?

Respiratory System

A 20. Airw ay obst ruct ion usually occurs in t he unconscious pat ient and may be part ial or complet e. It may occur anyw here f rom t he nose or mout h dow n t o t he t rachea. There are many causes of an obst ruct ed airw ay: 䊏 䊏 䊏 䊏 䊏

䊏

Answ ers

Relaxat ion of t he sof t t issues (especially t he t ongue) in t he oropharynx Vomit , blood or ot her f oreign body Laryngospasm Facial t rauma Oedema of t he airw ay secondary t o burns or smoke inhalat ion, inf ect ion or inf lammat ion, and anaphylact oid react ions Low er airw ay obst ruct ion (sub-laryngeal) is less common and associat ed w it h: — Pulmonary secret ions and mucous plugging (common in ICU pat ient s) — Thoracic t rauma — Obst ruct ive airw ays – ast hma or emphysema (expirat ion) — Pulmonary oedema — Large pneumot horax/haemot horax

Clinical 䊏 䊏 䊏

Complet e obst ruct ion is silent Part ial obst ruct ion is noisy There may be paradoxical (see-saw ) movement s of t he chest and abdomen caused by uncoordinat ed movement s of t he respirat ory muscles

M anoeuvres designed t o keep t he upper airw ay pat ent aim t o achieve t he ‘sniff ing t he morning air’ posit ion w it h t he neck f lexed and head ext ended: 䊏 䊏 䊏

196

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Head t ilt – avoid in t rauma pat ient s Chin lif t Jaw t hrust – t his is t he saf est met hod f or pat ient s w it h suspect ed neck injury (in conjunct ion w it h in-line st abilisat ion)

Key Quest ions in Surgical Crit ical Care

These t echniques may be supplement ed by: 䊏 䊏

Definitive airway Endo-t racheal t ube: 䊏 䊏

Nasal is more comf ort able and t heref ore requires less sedat ion Oral makes suct ioning and f ibreopt ic examinat ion of t he low er airw ay easier

Respiratory System

䊏

Oropharyngeal (Guedel) airw ay Nasopharyngeal airw ay (not w it h suspect ed base-of -skull f ract ure) Laryngeal mask airw ay (LM A) – is relat ively easy t o insert and rest s in t he hypopharynx cushioned by an air-f illed cuff . Alt hough not a def init ive airw ay, t his can be used f or posit ive pressure vent ilat ion f or short periods or in an emergency (w it h a variable leak around t he cuff ).

Tracheost omy: 䊏

䊏

Answ ers

䊏

M ini-t racheost omy – usually as an emergency procedure f or vent ilat ion or expect orat ion and suct ioning of excessive low er airw ay secret ions. It is not suit able f or prolonged vent ilat ion since t he narrow bore of t he t ube does not allow adequat e CO2 clearance. Percut aneous – using a Seldinger t echnique. A f ibreopt ic scope may also be used t o aid visualisat ion. Surgical

Indications for a definitive airway 䊏

䊏 䊏 䊏

Prot ect ion of t he low er airw ay f rom aspirat ion by f ood, blood, secret ions or vomit (any pat ient w it h a GCS ⬍ 8 w ill need airw ay prot ect ion) Facilit at ion of posit ive pressure vent ilat ion By-passing any upper airw ay obst ruct ion Allow s regular suct ion of t he low er airw ay and aspirat ion of samples f or cult ure SCC pp 87–91

Q 21. What are the principle causes of ARDS? What clinical findings make up the diagnosis? A 21. ARDS is t he pulmonary component of t he syst emic inf lammat ory response syndrome (SIRS).

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Direct (pulmonary) causes 䊏 䊏 䊏

Respiratory System

䊏 䊏

Cont usion f rom blunt t rauma Aspirat ion of st omach cont ent s Near drow ning Inf ect ion Smoke or t oxic inhalat ion

Indirect (extra-pulmonary) causes 䊏 䊏 䊏 䊏 䊏 䊏 䊏 䊏

Sepsis M ajor t rauma Embolic episodes (t hrombot ic, f at or amniot ic) Pancreat it is M assive blood t ransf usion Severe or prolonged haemorrhage/hypot ension Disseminat ed int ravascular coagulopat hy (DIC) Cardio-pulmonary bypass

Answ ers

The incidence varies f rom 3 t o 6 per 105 in t he UK, upt o 80 per 105 of t he populat ion in t he USA. This variabilit y has much t o do w it h diff erences in diagnosis bet w een t he t w o count ries, w hich led t o a consensus conf erence f ormulat ing t he f ollow ing crit eria: 䊏 䊏 䊏 䊏 䊏

There must be a know n precipit at ing cause The onset of sympt oms must be acut e There must be hypoxia ref ract ory t o oxygen t herapy There must be new bilat eral, f luff y inf ilt rat es on t he CXR (t his sign may lag behind t he clinical pict ure by 12–24 hours) There must be no cardiac f ailure or f luid overload (t his is t o exclude t hese causes of t he t ypical CXR appearance in ARDS, and is t aken as a PAWP of ⬍18 mmHg)

The severit y of t he hypoxic insult can be quant if ied int o acut e lung injury (ALI) or ARDS depending on t he f ract ion of inspired oxygen t hat t he subject is breat hing: 䊏 䊏

In ALI t he PaO2:FIO2 rat io is ⬍40 kPa (300 mmHg) In ARDS t he PaO2:FIO2 rat io is ⬍27 kPa (200 mmHg)

The f ollow ing are associat ed clinical f indings (but are not included as diagnost ic crit eria): 䊏 䊏

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The need f or mechanical vent ilat ion Low lung compliance

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䊏

High airw ay pressures during posit ive pressure vent ilat ion SCC pp 91–96

A 22. The pat hophysiology of ARDS revolves around t he prot ect ive inf lammat ory response t o invasion by chemical or inf ect ive t oxins. This response is subject t o posit ive f eedback result ing in an uncont rolled and damaging series of event s t hat result in t he clinical f indings of ARDS.

Answ ers

In t he early st ages (w it hin 24 hours of t he precipit at ing event ) t here is neut rophil act ivat ion leading t o t he release of inf lammat ory mediat ors such as cyt okines, t umour necrosis f act or (TNF), plat elet act ivat ing f act or (PAF), int erleukin (IL1 and IL6) and prot eases. These inf lammat ory mediat ors cause direct capillary endot helial cell damage result ing in increased capillary permeabilit y. This leads t o a ‘leakage’ of prot ein rich exudat e, w hich f ills t he alveoli. The f luid f illed alveoli do not t ake part in gaseous exchange result ing in shunt f ormat ion and hypoxaemia. As t he f luid is reabsorbed t here is at elect ic collapse of t he aff ect ed alveoli w it h t he result ing loss of f unct ional lung unit s. Art erial hypoxaemia is compounded by direct damage t o lung parenchyma by t he inf lammat ory mediat ors.

Respiratory System

Q 22. Describe the pathophysiological processes responsible for ARDS? What is the prognosis?

The lat e st ages of ARDS are charact erised by f ibroblast prolif erat ion int o t he aff ect ed lung unit s, result ing in f ibrosis and collagen deposit ion. This leads t o microvascular oblit erat ion compounding t he vent ilat ion/perf usion mismat ch. Event ually t he pat ient may develop a clinical pict ure similar t o f ibrosing alveolit is, w it h rest rict ive lung disease sympt oms. The disease process is not unif orm w it hin t he lung, w it h some areas being spared and capable of gas exchange. Prognosis This is ext remely variable and t he mort alit y is increased by: 䊏 䊏

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Increasing age Signif icant past medical hist ory – especially renal or hepat ic f ailure

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199

䊏

䊏

Precipit at ing cause – sepsis has t he highest mort alit y and polyt rauma (provided t he pat ient survives t he init ial event ) has t he low est Associat ed complicat ions increase morbidit y and can w orsen mort alit y

Respiratory System

Early deat hs are of t en relat ed t o t he precipit at ing cause, lat e deat hs are f requent ly associat ed w it h mult i-organ f ailure (M OF). M any survivors have lit t le or no residual problems; ot hers w ill have a range of disabilit y f rom a reduced exercise t olerance t o sympt oms and signs of f ibrot ic lung disease. SCC pp 91–96

Q 23. What are the objectives for respiratory support in a patient with ARDS? What mechanisms are there to maintain adequate oxygenation?

Answ ers

A 23. The aim is t o achieve reasonable levels of oxygenat ion and CO2 removal w it hout any f urt her damage t o t he lungs. This may require a compromise bet w een adequat e vent ilat ion and prot ect ion of t he healt hy lung. This may be achieved by: 䊏 䊏

Permissible hypercapnia t o PaCO2 of 10–15 kPa (if no signs of acidosis of cerebral oedema) Accept able hypoxaemia t o PaO2 of 8 kPa (if no signs of ischaemia)

Methods of ventilatory support Collapsed areas of t he lung may be expanded by alveolar recruit ment manoeuvres designed t o increase t he FRC, t hereby improving oxygenat ion: 䊏

䊏

CPAP (5–10 cmH2O) can be used in spont aneously breat hing pat ient s in t he early st ages of t he disease, and may be administ ered via a nasal or f acemask. It is seldom eff ect ive f or long-t erm t herapy and is usually a holding measure. PEEP (10–15 cmH2O) can be used during mechanical vent ilat ion but is associat ed w it h haemodynamic inst abilit y.

Convent ional volume-cont rolled vent ilat ion w it h t idal volumes of 10–12 ml/kg can cause barot rauma and volut rauma t o t he healt hy areas of t he lung. These can be avoided by t he f ollow ing

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manoeuvres:

IRV – Normal inspirat ory (I) t o expirat ory (E) rat io is 1:2, but t his can lead t o high inf lat ion pressures because of t he relat ively short inspirat ory t ime and t he st iff lungs. The I:E rat io may be prolonged t o 1:1, 2:1 or 3:1. This w ill f urt her opt imise t he M AWP, so improving oxygenat ion f or any given PAWP. There are several problems associat ed w it h t hese met hods of vent ilat ion: 䊏 䊏 䊏

Haemodynamic inst abilit y Decrease in CO2 eliminat ion leading t o f urt her hypercapnia Deep sedat ion and paralysis are required since t his is a very unnat ural and uncomf ort able mode of vent ilat ion.

䊏

䊏

Prone ventilation (usually for 4–8 hours at a time). This strategy aims to decrease the collapse seen in the dependant areas of the lung by reducing the time that the patient spends in one position. Gradually the dependent areas in the new position will collapse and contribute towards hypoxaemia, and the position will need to be changed again. This can be very labour intensive for the nursing staff. Vent ilat ion on a rot at ing bed. By cont inuously moving t he pat ient t hrough 90⬚ areas of t he lung w ill only become dependent t ransient ly and t heref ore reduce t he incidence of collapse.

Answ ers

Resist ant hypoxaemia may benef it f rom improved mat ching of vent ilat ion (V) and perf usion (Q) by changing t he posit ion of t he pat ient :

Respiratory System

PCV – This generat es a charact erist ic square w avef orm so opt imising M AWP w it hout increasing (PAWP). The upper pressure is limit ed t o t hat set on t he vent ilat or. This is usually set t o 30–40 cmH2O.

Bot h of t hese manoeuvres are made more hazardous by t he use of mult iple inf usion lines or haemof ilt rat ion. Prost acyclin and nit ric oxide (NO) also know n as endot helium derived relaxant f act or (EDRF). When delivered via a specialised circuit t hese agent s select ively vasodilat e t he pulmonary vascular beds t hat are adequat ely vent ilat ed, t hus improving V/Q mat ching and improving hypoxaemia. SCC pp 91–96

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Other Systems and Multisystem Failure

Answ ers

Q 1.

What are the indications for a computed tomography (CT) scan following a head injury?

A 1.

Wit h t he advent of high-speed spiral scanners, comput ed t omography (CT) scans are used liberally in t he management of head injury. General guidelines f or a CT scan are: 䊏 䊏 䊏 䊏 䊏 䊏

Det eriorat ion in conscious level as assessed by t he Glasgow coma score (GCS) or development of pupillary signs Development of f ocal neurological signs Skull f ract ure The pat ient remains conf used or in a st at e of unconsciousness The pat ient is diff icult t o assess e.g. alcohol Penet rat ing injury SCC pp 99–107

Q 2.

What type of injuries are possible to blood vessels and what are their sequelae?

A 2.

Bot h art eries and veins can be injured by eit her t ransect ion (incomplet e or complet e), lacerat ion or closed injuries. Incomplet e t ransect ion: 䊏 䊏 䊏 䊏 䊏 䊏

Pulsat ile haemat oma Delayed haemorrhage False aneurysm Rupt ure Thrombosis and embolism Art eriovenous f ist ula

Complet e t ransect ion: 䊏 䊏 䊏 䊏 䊏

202

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Cont ract ion Ret ract ion Haemat oma Dist al ischaemia Pulse def icit

Key Quest ions in Surgical Crit ical Care

The ext ent of injury is of t en great er t han t he def ect . Pat ches are of t en required 䊏 䊏 䊏 䊏

Dist al t hrombosis Dist al ischaemia Haemat oma (pulsat ile) False aneurysm

Closed injury: 䊏 䊏 䊏 䊏 䊏

Thrombosis Int imal f lap or t ear Dissect ion Occlusion Spasm SCC pp 146–151

What are the causes of raised intracranial pressure (ICP) after head injury?

A 3.

The causes of raised int racranial pressure (ICP) af t er head injury are: 䊏 䊏 䊏 䊏 䊏

Answ ers

Q 3.

Other Systems and Multisystem Failure

Complicat ed lacerat ion w it h loss of t issue:

Haemat oma Focal cerebral oedema (cont usion or haemat oma) Diff use oedema Diff use brain sw elling Cerebrospinal f luid (CSF) obst ruct ion (rare)

Raised int racranial pressure (ICP) jeopardises cerebral perf usion (Cerebral perf usion pressure (CPP) ⫽ M ean art erial pressure (M AP) ⫺ ICP). SCC pp 99–107

Q 4.

What are the indications for urgent surgical exploration in thoracic trauma?

A 4.

Thoracic t rauma can result in eit her int rat horacic injury or int ra-abdominal injury, and t heref ore surgical explorat ion can be eit her t horacot omy or laparot omy (Table 3.1).

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Other Systems and Multisystem Failure

Table 3.1 Indicat ions f or surgical explorat ion in t horacic t rauma Indicat ions f or t horacot omy Init ial drainage ⬎1500 ml

Obvious int ra-abdominal injury

Drainage ⬎500 ml f or 3 or more hours

Posit ive DPL

Signs of occult haemorrhage w it h no ot her injury

Obvious diaphragmat ic injury

M assive air leak

Suspect ed penet rat ing diaphragmat ic injury

Praecordial penet rat ing injury Rupt ured aort a M assive chest w all def ect SCC pp 146–151

Answ ers

Q 5.

How do you decide how much fluid to give a patient with major burns?

A 5.

Fluid replacement with either colloid or crystalloid should be instigated as soon after a major burn as possible, and should be in line with one of the recommended regimens: e.g. Parkland (ATLS®). Weight (kg) ⫻ % Burn surf ace area ⫻ (2 t o 4)

This replacement is f rom t he t ime of t he burn and represent s f luid load f or t he f irst 24 hours. SCC pp 151–157

204

Q 6.

How do you diagnose and treat fat embolism syndrome (FES)?

A 6.

Signs and symptoms The signs and sympt oms of f at embolism syndrome (FES) can be divided int o respirat ory, cent ral nervous syst em (CNS) and ot her (Table 3.2).

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Key Quest ions in Surgical Crit ical Care

Respirat ory

CNS

Ot her

Dyspnoea Anxiet y Pet echial rash Tachypnoea Irrit at ion Ret inal haemorrhages Hypoxaemia* Conf usion Tachycardia CXR – Bilat eral inf ilt rat es Convulsions Fever Adult respirat ory dist ress CT – Cerebral oedema syndrome (ARDS) * Hypoxaemia can persist up t o 14 days

Diagnosis Diagnosis is made based on t he crit eria of Gurd and Wilson (Table 3.3). One major and f our minor crit eria are required, including f at macroglobulinaemia (⬎8 ␮m). Table 3.3 Gurd and Wilson’s Diagnost ic Crit eria f or FES M ajor

M inor

Laborat ory

Tachycardia

Acut e ↓ haemoglobin

Respirat ory sympt oms, signs or X-ray changes

Pyrexia

Sudden t hrombocyt openia

Cerebral signs unrelat ed t o head injury

Ret inal changes ↑ Eryt hrocyt e sediment at ion rat e (ESR)

Answ ers

Pet echial rash on upper ant erior body

Renal changes

Other Systems and Multisystem Failure

Table 3.2 Signs and Sympt oms of FES

Fat macroglobulinaemia

Jaundice Source: Gurd AR, Wilson RI. J Bone Joint Surg 1974: 58; 408–416

Treatment The mainst ay of t reat ment of FES is support ive. Respirat ory support (oxygen, cont inuous posit ive airw ay pressure (CPAP), int ermit t ent posit ive pressure vent ilat ion (IPPV)), cardiovascular support (maint enance of int ravascular volume and oxygen delivery w hich may require inot ropes), CNS support (cont rol ICP) and musculoskelet al support by immobilisat ion of f ract ures. SCC pp 158–160

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Other Systems and Multisystem Failure

Q 7.

What features of burn injuries would make you suspect an inhalational injury and how would you manage it?

A 7.

Inhalat ional injury is charact erised by evidence of laryngeal oedema (cough, st ridor, hoarse voice, carbon deposit s around mout h). Smoke inhalat ion is invest igat ed by measurement of carboxyhaemoglobin levels, art erial blood gases and f ibreopt ic bronchoscopy t o assess t he upper airw ay. Treat ment is principally of respirat ory support ; int ubat e and 100% oxygen, CPAP and posit ive end expirat ory pressure (PEEP), regular bronchodilat ors and chest physiot herapy. Complicat ions of smoke inhalat ion include airw ay compromise, oedema and obst ruct ion, w hich is an emergency. Ot her complicat ions include airw ay irrit at ion leading t o bronchospasm and mucus product ion, decreased lung compliance and increased lung lymph product ion.

Answ ers

SCC pp 151–157

Q 8.

How would you assess the severity of a head injury?

A 8.

First priorit ies are t o st abilise circulat ion and respirat ion (i.e. oxygenat ion, vent ilat ion and perf usion). This prevent s secondary damage. Assessment is by t he GCS – not just at one point in t ime but also t rends in t he GCS. Hist ory of t he injury including durat ion of amnesia (bot h ant egrade and ret rograde), mechanism of injury, and AM PLE (advanced t rauma lif e support – ATLS® ) hist ory. Examinat ion including f ull secondary survey, t reat ment of concomit ant injuries. Radiological invest igat ions including skull X-ray and CT scan as indicat ed. ICP monit oring is necessary in severe head injuries. SCC pp 99–107

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What are the causes of massive haemoptysis and how would you manage a patient with it?

A 9.

M assive haemopt ysis account s f or only 1.5% of all haemopt ysis. Any bleeding originat ing f rom t he bronchial art eries may cause lif e-t hreat ening haemopt ysis because of t he high pressure in t he bronchial art eries. The overall mort alit y rat e at t ribut ed t o massive haemopt ysis is largely inf luenced by malignant aet iologies and by t he rat e of bleeding. Causes include neoplasm, bronchiect asis, inf ect ions, vascular, vasculit is but ot hers also occur. Establish the source of the bleeding 䊏 䊏 䊏

Clinical history Salient point s in t he hist ory include: 䊏

䊏 䊏 䊏 䊏

䊏 䊏

Vivas

Answ ers

䊏

Haemorrhagic sit es f rom t he nasopharynx or t he gast roint est inal t ract should be excluded. M ajorit y of haemopt ysis prevalence originat es f rom t he bronchial art eries (90% ). Pulmonary art eries may be t he cause in only 5% . Bleeding t ends t o be more signif icant w hen coming f rom t he bronchial art eries because of high syst emic pressure.

Other Systems and Multisystem Failure

Q 9.

Ant icoagulant t herapy or coagulopat hies may cause haemopt ysis in pat ient s w it h no prior hist ory of lung diseases or haemopt ysis. Pulmonary t uberculosis may lead t o haemopt ysis caused by erosion of blood vessels. Prior diagnosis of cavit ary diseases such as t uberculosis, sarcoidosis, or chronic obst ruct ive pulmonary diseases. Bronchogenic carcinoma should be high in t he list among smokers ⬎40 years of age. Bronchial adenoma, vascular anomalies, and aspirat ion of f oreign bodies are very common causes of haemopt ysis among children. Pat ient s w it h congest ive heart f ailure secondary t o mit ral st enosis are at risk f or haemopt ysis. A hist ory of deep vein t hrombosis may lead t o pulmonary inf arct and embolism.

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Other Systems and Multisystem Failure

䊏

Febrile condit ions w it h pulmonary inf ect ions (lung abscess, necrot ising pneumonia) may be complicat ed by massive haemopt ysis.

Physical examination 䊏 䊏 䊏

The presence of st ridor or w heezing should raise t he suspicion of t racheolaryngeal t umours or f oreign body. Concomit ant haemat uria suggest s a diagnosis of Goodpast ure’s syndrome. Clubbing may be a sign of lung carcinoma or bronchiect asis.

Diagnostic studies 䊏

Answ ers

䊏 䊏

䊏

Sput um examinat ion – Sput um should be examined f or t he presence of bact eria (Gram st ain and acid-f ast bacillus). A smear f or cyt ology should be done if t he pat ient is ⬎40 years of age and a smoker. A specimen should also be obt ained f or cult ure, especially f or mycobact erium and f ungus. Chest radiography – M ay ident if y lung parenchymal pat hologies (e.g. t umours). Bronchoscopy – Rigid bronchoscopy is recommended in t he event of massive haemopt ysis because of it s great er suct ioning abilit y and maint enance of airw ay pat ency. Failure t o visualise t he upper lobes or peripheral lesions remains a major limit at ion w it h rigid bronchoscope. Inst illat ion of a vasoact ive drug direct ly int o t he bleeding bronchus t hrough t he bronchoscope channel may st op t he haemorrhage. CT – CT may demonst rat e lesions t hat may not be visible in t he chest radiograph, such as bronchiect asis or small bronchial carcinoma. When perf ormed w it h cont rast mat erial, CT may det ect t horacic aneurysm or art eriovenous malf ormat ions.

Management 䊏 䊏 䊏

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Resuscit at ion Vit al signs and oxygen sat urat ion should be monit ored in t he int ensive t herapy unit (ITU). Blood invest igat ions including f ull blood count , art erial blood gas, coagulat ion prof ile, elect rolyt es, t ype and cross-mat ch (minimum of 6 unit s of packed red cells), renal and liver f unct ion t est s.

Key Quest ions in Surgical Crit ical Care

䊏

䊏

䊏

䊏

Answ ers

Int ubat ion is necessary f or lif e-t hreat ening haemopt ysis, hypovolemic shock, w orsening hypoxemia in spit e of supplement al oxygen or an elevat ed CO2 concent rat ion. Surgery and ot her invasive met hods: — Surgery remains t he procedure of choice in t he t reat ment of massive haemopt ysis caused by leaky aort ic aneurysm, art eriovenous malf ormat ions, iat rogenic pulmonary rupt ure, chest injuries, and bronchial adenoma. Endobronchial t amponade (occluding t he bleeding bronchus w it h a balloon cat het er). The insert ion of t hese cat het ers necessit at es t he use of a rigid or f lexible bronchoscope. Bronchial art ery embolisat ion (BAE) is now considered t he most eff ect ive non-surgical t reat ment in massive haemopt ysis because of immediat e and long-t erm result s. Select ive angiography should be perf ormed init ially t o locat e t he bleeding bronchial art ery bef ore inject ion. Conservat ive management . Invasive t herapeut ic measures are not indicat ed in t he cont rol of haemopt ysis caused by ant icoagulant t herapy or blood dyscrasia. These condit ions can be t reat ed by appropriat e medical t herapy.

Other Systems and Multisystem Failure

䊏

Q 10. How would you manage a patient with acute hepatic failure (AHF)? A 10. The aims of management of acut e hepat ic f ailure (AHF) are t he prevent ion of complicat ions, namely inf ect ion, cerebral oedema and mult iple organ f ailure and t o opt imise condit ions f or hepat ic regenerat ion. The ot her principle is t he ident if icat ion of pot ent ial t ransplant recipient s. Early t ransf er t o a specialist unit is recommended. The mainst ay is support ive t herapy. Precipit at ing f act ors f or AHF should be reversed w here possible (GI bleed, renal f ailure). Oral lact ulose should be administ ered and diet ary prot ein decreased. Ot her syst ems should be support ed; f luid replacement – 5% dext rose is f luid of choice, inot ropes f or cardiovascular syst em (CVS), mechanical vent ilat ion ⫾ PEEP f or RS and M annit ol 0.5 g/kg ⫾ Frusemide f or cerebral oedema. 䊏

Vivas

Inf ect ion should be cont rolled, considering select ive decont aminat ion of t he gut w it h neomycin.

Key Quest ions in Surgical Crit ical Care

209

Other Systems and Multisystem Failure

䊏 䊏

Support ot her syst ems. Liver assist devices are undergoing st udies at present . SCC pp 135–139

Q 11. What are the clinical features of a raised ICP? A 11. Normal ICP is approximat ely 10 mmHg. Pressures over 40 mmHg are severely abnormal and associat ed w it h poorer out comes. The ICP may remain normal unt il decompensat ion occurs. Det eriorat ion f ollow ing head injury is almost alw ays due t o increased ICP. Increased ICP may be caused by eit her cerebral oedema or ext ra-cerebral compression (ext radural or subdural haemat omat a). Compression is usually associat ed w it h a progressive course, w hich may be rapid.

Answ ers

As w ell as neurological det eriorat ion, ot her indicat ions of raised ICP include pupillary dilat at ion, hemiparesis, hemiplegia and decrebrat ion. Raised ICP due t o ext ernal compression requires rapid decompression and raised ICP due t o cerebral oedema usually requires medical management w it h mannit ol. SCC pp 99–107

Q 12. How would you manage a patient with a spinal cord injury? A 12. At t he scene of accident it is necessary t o maint ain in-line spinal immobilisat ion w hich requires support ing of neck w it h st iff collar and sandbags and t he pat ient should be t ransport ed on spinal board. The init ial priorit ies of hospit al management of spinal injury pat ient s remain ABC. History A spinal injury should be suspect ed if any major accident , unconscious pat ient , f all f rom a height , sudden jerk of neck af t er rear end car collision, f acial injuries or head injury. Direct ly ask about neck or back pain, numbness, t ingling, w eakness, abilit y t o pass urine. 210

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Key Quest ions in Surgical Crit ical Care

䊏

䊏

Answ ers

Primary survey — Int ubat ion if necessary requires maint enance of in-line immobilisat ion. — Pharyngeal st imulat ion w it h airw ay can cause vagal discharge and cardiac arrest . — Cervical spine injuries reduce sympat het ic out f low. — Pat ient s may be bot h hypot ensive and bradycardic (not a f eat ure of hypovolaemia t heref ore suspect spinal cord injury). — Aggressive f luid resuscit at ion can induce pulmonary oedema. Secondary survey — Logroll – look f or bruising, palpat e f or a st ep, t enderness. — Repeat ed neurological examinat ion t o det ermine neurological damage and it s progression/resolut ion. — Syst emat ic examinat ion f or f ract ures as pat ient may not f eel pain. — In t et raplegic pat ient s respirat ory f ailure may be due t o int ercost al paralysis, part ial phrenic nerve palsy, impaired abilit y t o cough or a vent ilat ion-perf usion mismat ch. — In paraplegic pat ient s respirat ory f ailure may be due t o variable int ercost al nerve paralysis or associat ed chest injuries. — M ay develop as a lat e f eat ure due t o ascending oedema in t he cervical cord. — Abdomen may be f laccid w it h absence of sensat ion (f eat ures of perit onism may be absent ). — Priapism may develop.

Other Systems and Multisystem Failure

Examination

Imaging 䊏

䊏

Vivas

X-rays – Cervical spine AP, lat eral including C7/T1 (sw immers view or pull arms dow n t o visualise), open mout h view of odont oid peg. AP and lat eral view of ot her t ender areas of spine. Image t he ent ire spine if a spinal f ract ure is present . CT scan show s bony injury, magnet ic resonance imaging (M RI) scan show s sof t t issue involvement .

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Other Systems and Multisystem Failure

If neurological damage: 䊏 䊏 䊏 䊏

䊏

Insert a urinary cat het er. Not e reduced BP and bradycardia due t o neurogenic shock. Exclude hypot ension due t o haemorrhage elsew here. Invasive monit oring is required. Give met hylprednisolone int ravenous 30 mg/kg over 15 minut es t hen 5.4 mg/kg/hr f or next 23 hours. Needs t o be given w it hin 8 hours. Discuss w it h local spinal injuries unit . Pressure area care – regular t urning. SCC pp 108–112

Q 13. What methods are employed to try to prevent multi-organ dysfunction syndrome (MODS)? A 13. Prevent ion can be grouped int o t hree broad t ime periods; t he resuscit at ion phase, t he operat ive phase and t he int ensive care phase.

Answ ers

Resuscit at ion

Along t he lines of ATLS principles: Airw ay, breat hing, circulat ion, w it h t he object ives being t o maint ain organ perf usion and oxygenat ion.

Operat ive t reat ment

Early, appropriat e operat ive int ervent ion, w it h clear object ives. This is t he saf est w ay. A planned second procedure is of t en bet t er t han w ait ing unt il complicat ions occur.

Int ensive care unit (ICU) management

St andard ICU pract ice of vent ilat ory support , renal support , ant ibiot ics t hat are appropriat ely t arget ed and appropriat e nut rit ion. SCC pp 112–116

Q 14. How would you manage a patient with a severe upper gastrointestinal bleed? A 14. The principles are resuscit at e, invest igat e and t hen endoscopy. Resuscit at ion t akes t he f orm of circulat ory support w it h t w o large-bore cannulae, and f luid t herapy w it h cryst alloid or t ransf usion. Normal saline should be avoided in pat ient s w it h suspect ed liver disease. 212

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Endoscopy should be perf ormed on t he next list af t er resuscit at ion unless t he bleeding is prof use. Non-variceal bleeding can be t reat ed endoscopically using t hermal probes, inject ion of epinephrine or sclerosant s, clips, st aples or sut ures, or a combinat ion. Variceal bleeding can necessit at e t he insert ion of a Sengst akenBlakemore t ube as a t emporising measure. A t ransjugular int rahepat ic port osyst emic shunt (TIPSS) may be necessary. Surgery is reserved f or f ailure of endoscopic t herapy. SCC pp 129–131

Q 15. How would you manage a patient with blunt chest trauma?

Answ ers

A 15. The physiological consequences of blunt chest t rauma are alt ered vent ilat ory mechanics, decreased oxygenat ion, increased shunt ing and painf ul breat hing result ing in inhibit ion of coughing leading t o sput um ret ent ion and decreased t idal volume.

Other Systems and Multisystem Failure

Invest igat ions include haemoglobin w hich may remain normal unt il haemodilut ion occurs, urea and elect rolyt es (urea is elevat ed in severe bleeds), cross-mat ch, liver f unct ion t est s and prot hrombin t ime.

The eff ect s of t he chest injury and t hese physiological changes are hypoxia and hypercarbia leading pot ent ially t o ARDS. Treat ment is aimed at prevent ing ARDS and reversing t hese physiological changes. Oedema is prevent ed by f luid rest rict ion, physiot herapy can help prevent at elect asis. Oxygenat ion is increased by increasing FIO2. Lif e t hreat ening injuries such as t ension or open pneumot horax, massive haemot horax and f lail chest need t o be excluded. This should be done during t he primary survey. A chest radiograph w ill reveal most abnormalit ies. During t he secondary survey art erial blood gases should be measured and an elect rocardiogram (ECG) is perf ormed. Blunt cardiac and lung injuries should be sought . A chest t ube should be considered f or haemot horaces, pneumot horaces or any pat ient undergoing posit ive pressure vent ilat ion or aerial evacuat ion. Analgesia f or rib f ract ures w ill f acilit at e breat hing. SCC pp 146–151

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Q 16. What is systemic inflammatory response syndrome (SIRS) and how would you diagnose it? A 16. The syst emic inf lammat ory response syndrome (SIRS) is a prot ect ive response by t he body t o at t ack f rom pat hogens or ot her insult result ing in t issue damage. Posit ive f eedback perpet uat es t he response leading t o an unopposed inf lammat ory st at e giving t he t ypical clinical pict ure of SIRS. The primary precipit at ing event result s in t issue injury t hrough inf ect ion, t rauma, t umour invasion, hypoxia or ischaemia. The main causes are: 䊏 䊏 䊏 䊏 䊏

Localised or generalised sepsis Perit onit is (especially associat ed w it h pancreat it is) Burns Trauma Haemorrhage (part icularly w hen associat ed w it h hypot ension and hypoperf usion)

Answ ers

There t hen f ollow s a secondary inf lammat ory response. The immune syst em is alert ed t o t he t hreat posed by t he t issue damage and react s by inst it ut ing an inf lammat ory response t o prot ect t he body. This becomes exaggerat ed and subject t o repeat ed posit ive f eedback, leading t o uncont rolled propagat ion by t he inf lammat ory mediat ors involved. This result s in endot helial cell damage and breakdow n, causing t he det riment al eff ect s observed in SIRS. This cascade involves several inf lammat ory mediat ors w hich are represent ed in Table 3.4. Table 3.4 Inf lammat ory M ediat ors in SIRS Cyt okines Tumour Necrosis Fact or (TNF) Int erleukins (IL1, IL6) Plat elet Act ivat ing Fact or (PAF)

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Arachidonic acid derivat ives

St ress hormones

Ot her mediat ors

Prost aglandins

Cat echolamines

Hist amine

Leukot rienes

St eroids

Serot onin

Thromboxanes

Insulin

Bradykinin

Key Quest ions in Surgical Crit ical Care

䊏 䊏 䊏 䊏

Core t emperat ure ⬎38⬚C or ⬍36⬚C Heart rat e (HR) ⬎90/min Respiratory rate (RR) ⬎ 20/min or PaCO2 ⬍ 4.26 kPa (32 mmHg) Whit e cell count (WCC) ⬎12 ⫻ 109/l or ⬍4 ⫻ 109/l (w it h ⬎10% neut rophils or immat ure f orms)

Gast roint est inal t ract (GIT) bact erial t ranslocat ion and t he t ransf er of endot oxin via t he hepat ic port al venous syst em may be an import ant f act or as a const ant t riggering mechanism in t he propagat ion of t his exaggerat ed response. Nit ric oxide (NO) also ref erred t o as endot helium-derived relaxing f act or (EDRF) is involved in t he t onic relaxat ion of vascular smoot h muscle, opposing t he myogenic cont ract ion of t he vessel w alls. Wit h t he onset of SIRS, t he homeost asis of vascular t one is alt ered, and NO mediat ed vasodilat at ion predominat es, leading t o t he clinical eff ect s seen in t his condit ion.

Answ ers

Clinical effects of SIRS These w ill vary depending on t he precipit at ing cause and degree of involvement .

Other Systems and Multisystem Failure

The diagnosis of SIRS is made by t he pat ient f ulf illing t w o or more of t he f ollow ing crit eria:

There may be: 䊏 䊏 䊏 䊏 䊏 䊏 䊏

Overt or occult inf ect ion Flushed, w arm peripheries Hypot ension (part icular diast olic) Tachycardia Hypoxia M et abolic acidosis on art erial blood gas (ABG) (due t o hypoperf usion and lact ic acid accumulat ion) Deranged clot t ing f unct ion (since t he coagulat ion cascade may be involved in t he inf lammat ory response) SCC pp 112–116

Q 17. What is MODS? A 17. M ult i-organ dysf unct ion syndrome (M ODS) is a progression f rom SIRS, result ing in end-organ dysf unct ion. It is diagnosed by dysf unct ion of t w o or more organ syst ems. The inf lammat ory

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process result s in hypoperf usion and ischaemia of t he t issues. The clinical pict ure w ill depend on t he organ syst ems aff ect ed. Respiratory Of t en involved since t hey receive all of t he cardiac out put . Acut e lung injury (ALI) and ARDS may occur f ollow ing SIRS. The pat ient w ill be hypoxic, and show signs and sympt oms of respirat ory f ailure. Cardiovascular Endot helial damage leads t o ext raversat ion of f luid f rom t he vessels int o t he int erst it ium result ing in oedema. Vasodilat at ion of art eries and veins result in hypot ension, w it h t issue hypoxia and lact ic acidosis. There may be myocardial dysf unct ion result ing f rom t he direct eff ect s of inf lammat ion on t he heart and circulat ing mediat ors or endot oxin (in sepsis).

Answ ers

Renal There is oliguria (⬍0.5 ml/kg/hr of urine product ion) because of reduced renal perf usion and f ilt rat ion of inf lammat ory mat t er. Urea and creat inine may be elevat ed. Hepatic Hypoperf usion result s in reduced met abolism of drugs and hormones, poor cont rol of glucose homeost asis, synt het ic f ailure e.g. coagulat ion f act ors and f ailure t o conjugat e bilirubin (jaundice). The immunological role of t he liver may be compromised; reducing t he abilit y t o det oxif y t ranslocat ed bact eria f rom t he GIT, t hereby w orsening SIRS. Test s of ext rinsic coagulat ion and liver f unct ion may be abnormal. GIT Hypoperf usion and ischaemia result s in at rophy. This increases t he risk of bact erial t ranslocat ion, t hereby cont inuously t riggering t he inf lammat ory response. Cerebral There may be conf usion, sedat ion or agit at ion. Haematological There may be anaemia, t hrombocyt openia, leucopenia, or leucocyt osis. The t est s of coagulat ion may show a range of

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If M ODS is allow ed t o cont inue unchecked t hen t he organ dysf unct ion w ill become irreversible. At t his st age, mult i-organ f ailure is said t o have occurred. This progression is pot ent ially avoidable w it h appropriat e t reat ment . SCC pp 112–116

Q 18. What are the principles of management in MODS? A 18. The t reat ment aims are t o support t he organ-syst ems aff ect ed, and improve t issue perf usion and oxygenat ion. Opt imisat ion of oxygen delivery (DO2) t o t he t issues: DO2 ⫽ CO ⫻ (1.34 ⫻ Hb ⫻ Sat /100) ⫹ dissolved f ract ion

DO2 can be maximised by maint aining adequat e: 䊏 䊏 䊏 䊏 䊏 䊏

Preload – f luid opt imisat ion t o increase st roke volume (SV). Af t erload – ␣-agonist s t o increase syst emic vascular resist ance (SVR). Inot ropic f unct ion – ␤-agonist s t o increase SV. Chronot ropic f unct ion – ␤-agonist s t o increase HR. Haemoglobin concent rat ion – t his should be maint ained above 10 g/dl. Haemoglobin sat urat ion should be maint ained above 94% . This may require mechanical vent ilat ion.

Answ ers

w here CO (cardiac out put ) ⫽ SV ⫻ HR and BP ⫽ SVR ⫻ CO dissolved f ract ion ⫽ (PaO2 ⫻ 0.003)

Other Systems and Multisystem Failure

abnormalit ies f rom prolonged int rinsic (APPT) and ext rinsic (PT) clot t ing t imes t o f rank disseminat ed int ravascular coagulopat hy (DIC).

Searching f or and t reat ing sources of sepsis: These may be t he primary precipit at ing cause responsible f or SIRS or secondary colonisat ion, part icularly in an immunocompromised host . Despit e t he act ive inf lammat ory response, t he body’s abilit y t o deal w it h act ive inf ect ion is of t en low. The use of rout ine ant ibiot ics cannot be recommended. Frequent t issue samples should be cult ured and ant imicrobial t herapy direct ed at posit ively ident if ied pat hogens. In overw helming or part ially t reat ed inf ect ion, posit ive cult ures may be impossible t o isolat e. Blind t herapy should be inst it ut ed

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only w it h t he close involvement of t he microbiology depart ment . Inappropriat e t herapy may generat e resist ant st rains and make f urt her t reat ment diff icult . M aint ain adequat e urine out put (⬎0.5 ml/kg/hr): This w ill require caref ul f luid t it rat ion, of t en w it h invasive monit oring of cent ral venous pressure (CVP or PAOP). Haemof ilt rat ion may be required. Prevent ion of malnut rit ion: These pat ient s are cat abolic and have increased energy requirement s, t heir increased subst rat e demand should be ref lect ed in nut rit ional regimens. The aim of t he t reat ment out lined above is t o avoid progression t o mult i-organ f ailure syndrome (M OFS), w hich is a progression f rom M ODS. This implies t hat irreversible damage has been done t o t he organ syst ems aff ect ed causing t hem t o f ail.

Answ ers

Prognosis The risk of mort alit y depends on many f act ors (Table 3.5): 䊏 䊏 䊏 䊏 䊏

Age Pre-morbid healt h Severit y of disease The presence of sepsis Number of organ syst ems aff ect ed and t he durat ion of f ailure

Table 3.5 M ort alit y rat es in M OFS Number of f ailed organ syst ems

M ort alit y on 1st day of organ f ailure

M ort alit y on 4t h day of organ f ailure

50% 80%

65% 95%

2 3

SCC pp 112–116

Q 19. What are the advantages and disadvantages of enteral nutrition? A 19. Ent eral nut rit ion can t ake many f orms: 䊏 䊏

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Oral supplement s Ent eral t ube f eeding

Key Quest ions in Surgical Crit ical Care

Advantages 䊏 䊏

䊏 䊏

䊏 䊏

Cheap and simple t o implement No cent ral venous access required — ↓ risk of inf ect ion — ↓ risk of mechanical complicat ions of insert ion M aint ains t he physiological role of t he GIT Improved GIT blood f low : — prevent s breakdow n of mucosal lining — prevent s t ranslocat ion of GIT bact eria — prevent s t he development of SIRS and M ODS

Disadvantages 䊏 䊏 䊏

䊏 䊏 䊏 䊏 䊏

Answ ers

Prot ect s against st ress ulcerat ion Early commencement (w it hin t he f irst 24 hours) — ↓ ICU st ay — ↓ sept ic complicat ions — part icularly t rue in mult i-t rauma

Other Systems and Multisystem Failure

— Nasogast ric — Nasojejunal — Percut aneous gast rost omy (PEG) (unusual in t he crit ically ill) — Percut aneous jejunost omy (PEJ) (usually af t er surgery)

Need f unct ioning GIT ↑ risk of nosocomial pneumonia Delivery syst em (t ubes) are source of morbidit y: — Nasal ulcerat ion — Sinusit is — Traumat ic removal (poorly t olerat ed by some pat ient s) — Tube occlusion — Displaced t ubes — Perit onit is w it h percut aneous t ubes — Bact erial colonisat ion Low er oesophageal sphinct er (LOS) dysf unct ion can lead t o regurgit at ion and aspirat ion of f eed ↑ incidence of diarrhoea ↑ incidence of nausea and vomit ing M alabsorpt ion leads t o malnourishment , w hich can be diff icult t o det ect Hyperglycaemia SCC pp 140–146

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Q 20. What are the advantages and disadvantages of parenteral nutrition? A 20. Advantages 䊏 䊏 䊏

All of prescribed f eed reaches t he bloodst ream Rest s damaged areas of t he GIT Fluid input may be precisely recorded

Disadvantages 䊏

䊏 䊏

Answ ers

䊏 䊏

Cent ral venous access required — Invasive — expert ise needed — inf ect ion risk — associat ed morbidit y Expensive Unphysiological — f at t y liver may result f rom lipid load — ↑ insulin requirement s GIT at rophy No prot ect ion f rom st ress ulcerat ion SCC pp 140–146

Q 21. How may nutrition regimens be tailored to patients with organ dysfunction? A 21. Cardiac Low Na⫹ and low H2O t o decrease t he risk of f luid overload and oedema product ion. Respiratory Aim t o decrease t he respirat ory quot ient (RQ) by increasing f at and reducing carbohydrat e cont ent . RQ is t he amount of CO2 produced per unit O2 ut ilised. RQ f or carbohydrat e is 1 and 0.7 f or f at . A high f at /low carbohydrat e diet w ill reduce CO2 product ion by t he t issues, t hereby decreasing t he w orkload of t he respirat ory syst em. Renal Reduce prot ein cont ent t o decrease urea product ion in t he liver. Renal pat ient s also have poor handling of high f at diet s. There should be reduced volume (↓H2O and ↓Na⫹ ) t o prevent f luid 220

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Liver Decreased H2O and Na⫹ cont ent t o prevent t he development of f luid overload, part icularly in pat ient s w it h ascit es. Nit rogen cont ent should be low ered in encephalopat hic pat ient s. There should be an adequat e carbohydrat e load since t here is a t endency t ow ards hypoglycaemia, due t o reduced glycogen st orage. Cerebral Glucose is t he main subst rat e in t he brain. Close blood sugar cont rol is required, as hyperglycaemia w orsens cerebral oedema, and hypoglycaemia result s in t issue damage.

SCC pp 140–146

Answ ers

St ressed pat ient have a t endency t o hyperglycaemia due t o t he eff ect s of adrenaline and noradrenaline on glucose handling. The ‘f ight ’ or ‘f light ’ response liberat es glucose f rom glycogen st ores in preparat ion f or act ion. Limit glucose t o 5 g/kg/day. Insulin sliding scale may be required.

Other Systems and Multisystem Failure

overload. Since t hey have a t endency t ow ards hyperkalaemia K⫹ should be avoided and monit ored regularly.

Q 22. What are the daily nutritional requirements of patients and how may these vary with critical illness? A 22. This depends on: 䊏

Size w hich is assessed by body mass index (BM I) (also know n as t he Quat elet index) BMI =

䊏 䊏

Weight (kg) Height 2 (m2 )

— 20–25 is normal — ⬍19 is malnourished — 25–30 is overw eight — 30–35 is obese — ⬎35 is morbidly obese Pre-morbid nut rit ional st at us Current clinical condit ion and met abolic demands

Daily requirements These are divided int o prot ein and non-prot ein (carbohydrat e and f at ) energy. The proport ions of t hese w ill vary depending on

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t he individual needs of t he pat ient . It should be not ed t hat pat ient s receiving inf usions of propof ol require less f at added t o t heir f eed. Nit rogen balance ⫽ Int ake ⫺ Loss g N/day Prot ein Intake = (g N/ day) 6.25

Nit rogen requirement is 0.2 g/kg/day. This is usually 9 g N/day f or males and 7.5 g N/day f or f emales. 䊏 䊏

In non-cat abolic pat ient s, t his represent s 1 g N per 200 kcal energy In cat abolic pat ient s, t his represent s 1 g N per 80–100 kcal energy

Glut amine is an essent ial amino acid and it is import ant f or w ound healing and gluconeogenesis. It must be added t o f eed since it is unst able in solut ion. Energy requirement s are calculat ed f rom basal met abolic rat e (BM R), t his is usually 20–30 kcal/kg/day:

Answ ers

䊏 䊏

2500 kcal f or males 2000 kcal f or f emales

Table 3.6 Variabilit y in energy requirement s during crit ical illness Energy requirement s

Energy requirement s

Pat ient s being conscious, sit t ing or ambulat ory

Pat ient s being unconscious and sedat ed

Pyrexia

M echanical vent ilat ion

M alnut rit ion Sepsis and burns SCC pp 140–146

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Problems in Intensive Care

Answ ers

Q 1.

What are the differences between sepsis, severe sepsis and septic shock?

A 1.

Sepsis The syst emic response t o inf ect ion manif est ed by t w o or more of t he f ollow ing: 䊏 䊏 䊏 䊏

Temperat ure ⬎ 38 or ⬍36⬚C Heart rat e (HR) ⬎ 90 beat s per minut e Respirat ory rat e (RR) ⬎ 20 breat hs per minut e or hypervent ilat ion PaCO2 ⬍ 4.25 kPa WBC ⬎ 12 ⫻ 109/l or ⬍4 ⫻ 109/l or ⬎10% immat ure f orms

Severe sepsis Sepsis w it h organ dysf unct ion, hypoperf usion or hypot ension (Syst olic BP ⬍ 90 mmHg or a drop of more t han 40 mmHg). Septic shock Def ined as sepsis w it h hypot ension, despit e adequat e f luid resuscit at ion, along w it h t he presence of perf usion abnormalit ies. SCC pp 163–165

Q 2.

What are the features of occult intra-abdominal sepsis and how would you diagnose and treat it?

A 2.

The clinical f eat ures are abdominal dist ension, pain, rebound, guarding and perit onism. Also, t he presence of a mass, pyrexia (especially a sw inging pyrexia), a met abolic acidosis, neut rophilia and t hrombocyt openia. Diagnosis can be assist ed by ult rasound and comput erised t omography (CT) but essent ially is surgical t hrough a laparot omy. Sw abs and samples should be sent f or cult ure including blood,

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urine, f aeces, abdominal drain f luid and any rect al or vaginal discharge.

Problems in Intensive Care

Treat ment is laparot omy (t his can be a diagnost ic procedure). Ant ibiot ics should be appropriat ely t arget ed w it h microbiological advice. Radiological drainage may be appropriat e under eit her ult rasonic or CT guidance.

Answ ers

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Principles of Intensive Care

Answ ers

Q 1.

What are the principles for the safe transfer of the critically ill surgical patient?

A 1.

The principles f or t he saf e t ransf er of t he crit ically ill surgical pat ient are: 䊏 䊏

䊏

䊏

䊏 䊏

䊏 䊏

䊏 䊏 䊏

Planning and communicat ion bet w een specialist s at bot h ref erring and receiving unit s Experienced st aff f or t he t ransf er – one experienced int ensive t herapy unit (ITU) doct or and one qualif ied ITU nurse/operat ing depart ment pract it ioner (ODP)/t echnician Appropriat e equipment and vehicle w it h good access, light ing and t emperat ure cont rol and a pow er supply f or t he relevant monit oring Full assessment and invest igat ion prior t o t ransf er – including elect rocardiogram (ECG), art erial blood gas (ABG), cent ral venous pressure (CVP), urine out put and chest X-ray. A pneumot horax should be excluded prior t o aerial t ransf er. Ext ensive monit oring t hat is robust , light w eight and bat t ery pow ered M et iculous st abilisat ion of t he pat ient including int ubat ion prior t o t ransf er. Vascular access should also be secure. Cont inual reassessment Cont inuing care during t ransf er – monit oring SaO2, CO2, heart rat e (HR), t emperat ure and int ra-art erial blood pressure (non-invasive blood pressure is diff icult t o measure w hilst in an ambulance or a helicopt er) Direct handover Communicat ion w it h relat ives Document at ion and audit SCC pp 189–191

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Principles of Intensive Care

Q 2.

What are the basics of successful clinical monitoring of the critically ill patient?

A 2.

Invasive and non-invasive measures For adequat e monit oring t he f ollow ing t ubes, lines and machines are necessary. 䊏

䊏 䊏 䊏 䊏 䊏

Venous access – t w o large bore peripheral cannulae, venous cut dow n or f emoral lines, t aking blood f or haemoglobin, biochemical prof ile and cross-mat ch Urinary cat het erisat ion allow ing monit oring of urine out put ECG – monit oring f or arrhyt hmias or ischaemia Pulse oximet ry (t ranscut aneous est imat ion of oxygen sat urat ion) Cent ral venous cat het erisat ion – CVP measurement Temperat ure measurement – core or peripheral

Answ ers

Clinical measurements St andard clinical measurement s include general appearance, respirat ory rat e (RR), pulse rat e, blood pressure, urine out put and CVP measurement . Regular investigations These include (but not exclusively) urea and elect rolyt es, haemoglobin, haemat ocrit , w hit e cell count , ABG, t emperat ure, pulmonary art ery occlusion pressure and a sepsis check. SCC pp 205–207

Q 3.

What parameters would make you consider early referral to critical care?

A 3.

Most hospitals have an early warning scoring system. An example is shown below. A score of three or more indicates a need to refer, but do not forget that trends are just as important as individual values. 3

2

1

0

HR ⬍40 41–50 51–100 M ean BP ⬍70 71–80 81–100 101–199 RR ⬍8 9–14 Temp ⬍35 35.1–36.5 AVPU* A

1

2

3

111–130 ⬎130 ⬎200 15–20 21–29 ⬎30 36.6–37.4 ⬎37.5 V P U 101–110

* A ⫽ Alert , V ⫽ Responds t o verbal commands, P ⫽ Responds t o pain, U ⫽ Unresponsive.

SCC pp 189–191

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What are the principles of analgesia in the multiple injured patient?

A 4.

Analgesia should be adequat e, appropriat e and observed. It can be syst emic or regional. Adequat e analgesia can f acilit at e breat hing (rib f ract ures). Appropriat e analgesia is int ravenous or int ramuscular opioid init ially. Non-st eroidal ant i-inf lammat ory drugs (NSAIDs) may also be appropriat e acut ely. Regional t echniques are usef ul in some cases but may mask compart ment syndrome and t heref ore liaison bet w een specialit ies is essent ial. Pat ient cont rolled analgesia (PCA) is also a usef ul t echnique. Monitoring of analgesic requirements is mandatory. If a patient’s analgesic requirement suddenly increases then think why – is it infection, an occult injury or a developing compartment syndrome?

Simple splint age of f ract ures w ill also reduce analgesic requirement s. SCC pp 203–205 Q 5.

What reasons might you want a surgical patient to go to intensive therapy unit (ITU) electively?

A 5.

The reasons are eit her f or monit oring or f or support . ABCDE is once again t he mnemonic: A B C D E

Answ ers

Syst emic opioids should be given in small quant it ies f requent ly. An NSAID may reduce opioid requirement s. Regional anaest hesia decreases respirat ory depression.

Principles of Intensive Care

Q 4.

Airw ay monit oring f or head and neck surgery Breat hing monit oring af t er cardiot horacic or upper abdominal surgery Circulat ory monit oring af t er cardiac and vascular surgery or in pat ient s w it h cardiovascular disease Disabilit y monit oring af t er neurosurgery Elect ive vent ilat ion f ollow ing cardiac or major abdominal surgery

The management plan should be f ormulat ed bet w een bot h anaest het ist and surgeon. Adequat e re-w arming and analgesia should be ensured and blood should be monit ored. SCC pp 189–191

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Principles of Intensive Care

Q 6.

What is meant by scoring systems for intensive care unit (ICU) patients? What scoring systems do you know?

A 6.

The principle aim of int ensive care is t o provide t he highest level and best qualit y of care available. This w ill involve evaluat ing t he out come af t er ICU t reat ment , w hich is diff icult f or t his group of pat ient s. The most f requent ly used det erminant of successf ul t reat ment is t he hospit al mort alit y rat e (w hich is t he deat h rat e bef ore discharge f rom hospit al of pat ient s w ho have been t reat ed in ICU). This does not t ake int o account t he qualit y of lif e t hereaf t er f or t he pat ient or t heir f amily. The aim of scoring syst ems used clinically is t o evaluat e out come f or diff erent groups of ICU pat ient s. These may be used t o: 䊏 䊏

Answ ers

䊏

Det ermine diff erent pat ient groups according t o t he severit y of illness At t ach risk t o each diff erent group: — For mort alit y rat e (survivabilit y) — For division int o separat e groups f or clinical t rials Compare diff erent ICUs in diff erent hospit als

These scoring syst ems do not predict out come or guide t reat ment planning f or individual pat ient s. Problems with scoring systems 1. Risk adjust ment t akes int o account t he diff erences bet w een pat ient s t hat aff ect t heir risk of any part icular out come, w hich is independent of t he care t hat t hey receive. Risk is increased by: 䊏 Increasing age 䊏 Signif icant pre-morbid illness 䊏 The admit t ing diagnosis 䊏 The severit y of t he present ing illness 䊏 Emergency surgery These f act ors const it ut e t he case mix, and case mix adjust ment is t he process of account ing f or t hese in t he det erminat ion and comparison of any out come measure (usually t he hospit al mort alit y rat e). 2. Select ion bias is an error in t he predict ive pow er if t he dat abase populat ion diff ers f rom t he sample populat ion, i.e. it has t o be validat ed f or t hat populat ion.

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The commonly used ICU scoring syst ems are: APACHE SAPS MPM

Acut e Physiology and Chronic Healt h Evaluat ion Simplif ied Acut e Physiology Score Mort alit y Probabilit y Models

These syst ems assign diff erent scores (w eight ing) t o t he measured variables. Scores are not only applied t o assess severit y of illness, but also severit y of t raumat ic injury sust ained. Those commonly used include: 䊏

䊏

Answ ers

䊏

Revised t rauma score (RTS) – t his correlat es w ell w it h survival. An RTS of 12 is associat ed w it h 99.5% survival, 6 w it h 63% survival and 0 w it h 3.7% survival Injury severit y scale (ISS) – scores seven body areas f rom 1 (minor) t o 5 (crit ical) Abbreviat ed injury score (AIS) – t his is calculat ed f rom t he sum of t he squares of t he t hree highest cat egories f rom t he ISS. From t his AIS score, t he let hal dose in 50% (LD 50) has been calculat ed as: — 40 (ages 15–44) — 29 (ages 45–64) — 20 (age ⬎ 65)

Principles of Intensive Care

3. Lead-t ime bias is t he eff ect of t reat ment (including t reat ment durat ion) on t he pat ient bef ore ent ering t he ICU. 4. There needs t o be a complet e and accurat e dat a set t o prevent errors f rom mult iplying.

SCC pp 198–201

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Answ ers

Q 1.

What are the complications of inserting an intercostal chest drain?

A 1.

The complicat ions are: 䊏 䊏 䊏

䊏

䊏

䊏

䊏

Damage t o t horacic or abdominal st ruct ures – t his is almost universally done by insert ing t he chest t ube w it h a t rocar Inf ect ion (empyema) Neurovascular damage — Bleeding leading t o haemot horax — Int ercost al neurit is Incorrect t ube posit ion — Ext ra-pleural — Sub-diaphragmat ic Tube complicat ion — Blockage — Dislodgement — Disconnect ion Persist ent pneumot horax — Large primary leak — Incomplet e seal at skin — Inadequat e underw at er seal Subcut aneous emphysema — Leak t hrough pariet al pleura but not t hrough skin SCC pp 221–223

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Q 2.

What are the indications for tracheostomy and what are its advantages?

A 2.

M ajor indicat ions are airw ay obst ruct ion, prot ect ion of t he t racheo-bronchial t ree and vent ilat ory insuff iciency. Airw ay obst ruct ion can be due t o t rauma (e.g. severe maxillo-f acial t rauma, severe head injury or severe f acial burns), inf ect ion (acut e epiglot t it is) or oedema. Prot ect ion of t he t racheobronchial t ree is necessary f or airw ay cont rol af t er major

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Advant ages of t racheost omy include decreased dead space, decreased w ork of breat hing, decreased sedat ive requirement s, increased eff iciency of suct ioning, it allow s speaking and eat ing, w eaning is quicker and int ensive t herapy unit (ITU) st ay is decreased. SCC pp 217–220

Describe how you would perform a venous cut-down of the long saphenous vein at the ankle.

A 3.

Venous cut -dow n is principally used f or emergency vascular access in t he t rauma sit uat ion. It may also be used w hen cent ral venous access is impossible. Any large vein is suit able alt hough t he long saphenous vein at t he ankle is t he f avoured sit e.

Answ ers

Q 3.

Practical Procedures

oropharyngeal surgery, or f ollow ing supraglot t ic surgery or head injury. Tracheost omy is usef ul f or vent ilat ory insuff iciency f or prolonged vent ilat ion (⬎2 w eeks) e.g. severe chest t rauma, coma or pulmonary diseases. M iscellaneous indicat ions f or t racheost omy include t o decrease anat omic dead space, t o f acilit at e t racheo-bronchial lavage and t o assist in vent ilat or w eaning.

The t echnique is similar f or all sit es. A t ransverse skin incision is made 2 cm ant erior and superior t o t he medial malleolus. The vein is dissect ed f ree by blunt dissect ion. Tw o t ies are placed around t he vein, t he dist al one secured t ight ly, and t he proximal loose. A vent omy is perf ormed. Insert a large 14G cannula int o t he venot omy and f lush t he cannula w it h 0.9% NaCl. The cannula is secured by t ight ening t he upper ligat ure. SCC pp 216–217

Q 4.

What are the findings for a diagnostic peritoneal lavage (DPL) to be positive?

A 4.

Diagnost ic perit oneal lavage (DPL) det ect s f ree int raperit oneal blood w it h 97% accuracy. A posit ive t est is indicat ed by any of t he f ollow ing: 䊏 䊏

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⬎10 ml f rank blood ⱖ 100,000 RBC/ml

Key Quest ions in Surgical Crit ical Care

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䊏 䊏 䊏 䊏

ⱖ 500 WBC/ml Bile/Bow el cont ent s drained f rom cat het er Gram st ain posit ive f or bact eria Perit oneal lavage f luid drained f rom cat het er or chest t ube

Practical Procedures

False posit ive result s may arise f rom haemorrhage f rom t he surgical incision or f rom bleeding f rom pelvic f ract ures. SCC pp 223–225

Q 5.

Why might you consider monitoring intra-abdominal pressure (IAP)?

A 5.

Int ra-abdominal pressure (IAP) is an import ant measure of underlying abdominal problems and an indicat or of a pat ient ’s physiological st at us. M onit oring of IAP in t he crit ically ill is gaining f avour. Slight increases in IAP have been show n t o have delet erious eff ect s on organ f unct ion. Clinical import ance of IAP: 䊏

Answ ers 䊏

IAP great er t han 10 mmHg has been demonst rat ed t o be inst rument al in organ dysf unct ion. Int ra-abdominal hypert ension (IAH) ⬎ 25 mmHg is delet erious t o bot h int ra- and ext ra-abdominal organs. IAH is an independent risk f act or f or int ensive care unit (ICU) mort alit y and has been demonst rat ed in 30% of a surgical ICU populat ion. Raised IAP aff ect s chest w all mechanics and decompression has benef icial eff ect s on respirat ory mechanics and oxygenat ion. SCC pp 228–229

Q 6.

What is a chest drain and how does it function?

A 6.

A chest drain is a conduit t o remove air or f luid (blood, pus or a pleural eff usion) f rom t he pleural cavit y. It allow s re-expansion of t he underlying lung and prevent s t he ent ry of air or drained f luid back int o t he chest . A chest drain must t heref ore have t hree component s, it must be unobst ruct ed, have a collect ing cont ainer below chest level and a one-w ay mechanism such as w at er seal or Heimlich valve. M echanism of act ion: Drainage occurs during expirat ion w hen pleural pressure is posit ive. Fluid w it hin pleural cavit y drains int o t he w at er seal

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t hrough w hich air bubbles. The lengt h of drain below t he f luid level is import ant : more t han 2–3 cm increases resist ance t o air drainage. SCC pp 221–223

What are the indications and potential complications of central venous cannulation?

A 7.

The Indicat ions are: 䊏 䊏 䊏 䊏 䊏 䊏 䊏 䊏 䊏

Complicat ions: 䊏 䊏 䊏

䊏 䊏 䊏 䊏 䊏 䊏

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Pneumot horax/haemot horax (more common w it h subclavian or low int ernal jugular approaches) Art erial punct ure (can be cat ast rophic w it h subclavian art ery rupt ure since t here is no w ay t o occlude t his vessel) Nerve injury — Phrenic, vagus and sympat het ic chain in t he neck — Femoral nerve in t he groin Cardiac arrhyt hmias Air embolus w it h neck cannulat ion in hypovolaemic pat ient s Erosion t hrough vessel w all (including myocardium) Format ion of A-V f ist ula Thoracic duct injury in t he neck (w it h lef t sided cannulat ion) Inf ect ion: — Use caref ul asept ic t echnique f or insert ion — Avoid sit es w it h skin eryt hema — TPN increases t he risk of inf ect ion and should be inf used via a dedicat ed line. Sit es should be changed regularly (every 5–7 days)

Key Quest ions in Surgical Crit ical Care

Answ ers

䊏

M onit oring of cent ral venous pressure (CVP) Fluid inf usion Drug inf usions (most inot ropes have t o be given cent rally) Blood sampling PA cat het er insert ion Triphosphopyridine nucleot ide (TPN) Haemof ilt rat ion Transvenous cardiac pacing Chemot herapy No possibilit y of peripheral venous access

Practical Procedures

Q 7.

233

䊏

Ect opic placement – t his is not alw ays avoidable but should be recognised: — Ensure t hat f ree aspirat ion of blood is possible — Check posit ion w it h CXR

Practical Procedures

Cont ra-indicat ions t o insert ion: 䊏 䊏

Bleeding diat heses (especially w it h t he subclavian rout e, since occlusion of a bleeding vessel is more diff icult ) Localised inf ect ion

These are relat ive and clinical need must be considered f or each individual case. SCC pp 211–214

Outline the relevant anatomy of a) the internal jugular vein (IJV) and b) the subclavian vein. Describe the technique used to cannulate each of these central veins.

A 8.

Internal jugular vein (IJV) Anat omy:

Answ ers

Q 8.

䊏 䊏

䊏

䊏 䊏

The IJV is f ormed f rom t he jugular bulb, w hich drains blood f rom t he brain via t he sigmoid sinus. It passes t hrough t he jugular f oramen and t hen f ollow s a st raight line t o t he st ernoclavicular joint , w here it joins t he subclavian vein t o f orm t he brachiocephalic vein. The IJV is int imat ely associat ed w it h t he int ernal carot id art ery t hroughout it s course – init ially post erior and f inally ant ero-lat eral t o it . The IJV, int ernal carot id art ery and vagus nerve all t ravel w it hin t he carot id sheat h. The IJV is superf icial in t he upper part of it s course, covered by t he st ernomast oid muscle in t he middle part and split s t he st ernal and clavicular heads of t hat muscle in t he low er part .

Cannulat ion t echnique: 䊏 䊏 䊏 䊏

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Head dow n posit ion Clean skin Inf ilt rat e w it h local anaest het ic A syringe should be at t ached t o needle at all t imes t o reduce t he risk of pneumot horax — M id/high approach – lat eral t o carot id art ery at t he level of t he cricoid cart ilage

Key Quest ions in Surgical Crit ical Care

䊏

Subclavicular vein (SCV) Anat omy: 䊏 䊏 䊏 䊏 䊏

Cont inuat ion of t he axillary vein Runs f rom t he lat eral border of t he f irst rib, and arches upw ards over t he rib It ’s most cephalad point is at t he mid-clavicular line Joins t he IJV t o f orm t he brachiocephalic vein behind t he st ernoclavicular joint The ext ernal jugular vein drains int o SCV

Practical Procedures

䊏

— Low approach – bet w een t he heads of st ernomast oid (reduced risk of art erial punct ure but increase risk of pneumot horax) Insert t he needle, and advance aiming t ow ards t he ipsilat eral nipple Once blood is aspirat ed cont inue w it h t he Seldinger t echnique

Cannulat ion t echnique: 䊏 䊏 䊏 䊏 䊏 䊏

Head dow n posit ion Clean skin Local anaest het ic inf ilt rat ion A syringe should be at t ached t o needle at all t imes t o reduce t he risk of pneumot horax The needle is insert ed at t he mid-clavicular line or junct ion of medial t hird and lat eral t w o t hirds of clavicle ‘Walk off ’ t he clavicle aiming t ow ards t he suprast ernal not ch Once blood is aspirat ed cont inue w it h t he Seldinger t echnique

Answ ers

䊏

Seldinger t echnique: 䊏 䊏

䊏 䊏 䊏 䊏 䊏 䊏 䊏

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Needle w it h syringe at t ached Once blood is f reely aspirat ed, det ach t he syringe and f eed t he guide w ire (w it h t he f lexible J t ip f irst ) f or approximat ely 15 cm Remove t he needle (t aking care not t o displace w ire) Ext end t he skin incision w it h a scalpel blade Advance t he dilat or over t he w ire (and remove) Insert t he cat het er over t he w ire Remove t he w ire Aspirat e blood and f lush all lines w it h heparinised saline CXR t o conf irm posit ion SCC pp 211–214

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