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182 PART IV MANAGEMENT CONSIDERATIONS
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Fleisher LA, Fleischmann KE, Auerbach AD, et al.: 2014 ACC/AHA Guideline on perioperative cardiovascular evaluation and
management of patients undergoing noncardiac surgery: executive summary, Circulation, August 1, 2014. [published online].
Glick M: New guidelines for prevention, detection, evaluation, and treatment of high blood pressure, J Am Dent Assoc
129:1588–1594, 1998.
Goldman L, Caldera DL, Nussbaum SR, et al.: Multifactorial index of cardiac risk in patients in noncardiac surgical proce-
dures, N Engl J Med 297:945–950, 1977.
McCabe JC, Roser SM: Evaluation and management of the cardiac patient for surgery, Oral Maxillofac Surg Clin North Am
10:429–443, 1998.
Muzyka BC, Glick M: The hypertensive dental patient, J Am Dent Assoc 128:1109–1120, 1997. Seres T: Congestive heart failure. In Duke J, editor: Anesthesia secrets, ed 3, Philadelphia, 2006, Mosby. Wilson W, Taubert KA, Gewitz M, et al.: Prevention of infective endocarditis: guidelines from the American Heart Association:
a guideline from the American Heart Association Rheumatic Fever, Endocarditis, and Kawasaki Disease Committee, Council on Cardiovascular.
PaO2= 100.1 − (0.323 × age in years)
RESPIRATORYDISORDERS
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Yedeh Ying, Zachary S. Peacock, Osama Soliman
1. What is the normal adult oxyhemoglobin dissociation curve for blood at 37%, pH of 7.4, and PCO2 of 40 mm Hg?
See Fig. 17-1.
2. What are the general rules concerning the dissociation curve shifts?
• AlowpHorahighPCO2shiftsthecurvetotheright.  • AhighpHoralowPCO2shiftsthecurvetotheleft.  • Elevatedbodytemperatureshiftsthecurvetotheright.  • Lowerbodytemperatureshiftsthecurvetotheleft.  • Carbonmonoxideinthebloodincreasestheafnityofremainingoxygenforhemoglobinandshifts
thecurvetotheleft.
3. How does the interpretation of the curve change when the curve shifts to the left?
TheP50isaconventionalmeasureofthehemoglobinafnityforoxygen.Ifthecurveisshiftedto
theleft,thereislessPO2(mmHg)inthebloodneededtoachievetheP50.Inotherwords,thereisan increasedhemoglobinafnitytoO2withaleftcurveshift.
4. What is 2,3-diphosphoglycerate (2,3-DPG)?
Itisproducedbyerythrocytesandnormallyispresentinfairlyhighconcentrationsinredbloodcells
(RBCs).
5. When is 2,3-DPG produced?
Itisproducedmainlyduringchronichypoxicconditions.Anincreasein2,3-DPGshiftsthecurvetothe
rightandallowsmoreO2tobereleasedfromhemoglobinataparticularO2level.Withadecreasein 2,3-DPG,thecurvewillshifttotheleft,indicatinganincreasedafnityforO2byhemoglobin.Hemo­globindoesnotreleaseO2inthetissuesexceptataverylowPO2.
6. How does 2,3-DPG affect blood supply in blood banks?
Bloodstoredforaslittleas1weekwillhavedepleted2,3-DPGunlessstepsaretakentorestore
normallevelsof2,3-DPG.
7. How does the aging process affect PaCO2?
PaCO2andalveolarventilationareunchangedbytheagingprocess.
8. How does the aging process affect PaO2?
PaO2decreaseswithage.Thisdecreasecanbecalculatedaccordingtothefollowingformula:
CHAPTER 17
ThusthePaO2ofa30-year-oldpersonwouldbecalculatedas100.1−(0.323×30)=90.41.
9. What are the anatomic volumes of the lungs?
TV:tidalvolume,theamountofairmovedwitheachbreath(Fig. 17-2) IRV:inspiratoryreservevolume,themaximumadditionalamountofairthatcanbeinhaledafterthe
endofinspiration IC:inspiratorycapacity,themaximumvolumeofairthatcanbeinspired(VT+IRV) RV:residualvolume,theremainingvolumeofairaftermaximalexpiration ERV:expiratoryreservevolume,themaximumadditionalamountofairthatcanbeexhaledafter
expiration FRC:functionalresidualcapacity,thevolumeinthelungsafterpassiveexpiration(RV+ERV) VC:vitalcapacity,themaximumamountofairthatcanbeexhaledaftermaximuminspiration
(IC+ERV) TLC:totallungcapacity,thevolumeinthelungsatmaximalinspiration(RV+VC)
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184 PART IV MANAGEMENTCONSIDERATIONS
6000mL
Time
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Percent saturation hemoglobin
Increased affinity
Acute alkalosis
100
Decreased PCO Decreased temperature Low levels of 2,3 DPG
90
Carboxyhemoglobin Methemoglobin
80
Abnormal hemoglobin
70
60
50
40
30
20
10
0
2
Normal
Decreased affinity
Acute acidosis High CO
2
Increased temperature High levels of 2,3 DPG Abnormal hemoglobin
200
Figure 17-1. Normaloxyhemoglobindissociationcurve.DPG,Diphosphoglycerate;COHb,carboxyhemoglobin;Hb,hemo­globin. (From Cairo JM, Pilbeam SP: Mosby’srespiratorycareequipment, ed 9, St Louis, 2009, Mosby.)
40 60
PO
(mm Hg)
2
80 100
Maximum
5000mL
4000mL
3000mL
2000mL
1000mL
inspiration
Maximum expiration
Inspiratory
reserve volume
Tidal volume
Expiratory
reserve volume
Residual volume
Vital
capacity
Inspiratory
capacity
Functional
residual capacity
Total
lung
capacity
0
Figure 17-2. Lungvolumesandcapacities. (From Nagelhout JJ, Plaus K: Nurseanesthesia, ed 4, St Louis, 2010, Saunders.)
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10. What are pulmonary function tests (PFTs), and why are they used?
PFTsareanadjuncttohistoryandphysicalexaminationandprovideanoverallassessmentofthe
respiratorysystem.Thetestsinclude(1)measurementsofairow(spirometry),(2)lungvolumes,and (3)diffusingcapacityforinspiredcarbonmonoxide(DLCO).Thetestsarereportedasapercentageof predictednormalvaluesbasedonageandheight.
11. What useful measurements are used in spirometry?
FVC:Forcedvitalcapacity FEV1:thevolumeofairthatcanforciblybeblownoutin1second,afterfullinspiration FVC/FEV1ratio:knownastheTiffeneau-Pinellindex
12. What is the normal FVC/FEV1 ratio?
ThenormalFVC/FEV1ratiois70%to80%.
13. What is the FVC/FEV1 ratio in obstructive and restrictive disease?
Inobstructivepulmonarydisease,expiratoryresistanceincreases,resultinginanincreaseintheFEV1.
TheFVCmayalsoincrease,butnottothesameextent,resultinginadecreasedratiobelow70%.In restrictivediseasesuchaspulmonarybrosis,theFVCandtheFEV1arebothreducedproportionally, resultinginanormalratioorevenincreasedasaresultofdecreasedlungcompliance.
14. How is the forced expiratory volume in 1 second (FEV1) changed with age?
FEV1declineslinearlywithageincrease.
15. What are the most significant changes of pulmonary function associated with aging?
• Lossoflungelasticity,whichleadstoincreasedmeanalveolardiameterandvolumeandreducedFEV  • Decreasedpoweroftherespiratorymusculature
1
• Increasedrigidityofribcage Allthesechangesstartbecomingapparentinthethirddecadeoflife.
16. What is the normal rate of breathing?
Thenormalrespiratoryrate(RR)is10to20breaths/mininadolescentsandadults(>12yearsold),
30to60ininfants(0to1year),24to40intoddlers(1to3years),22to34inthose3to6yearsold, and18to30inthose6to12yearsold.Foradolescentsandadults,anRR>20/minisconsidered tachypneaand<10/minisbradypnea.
17. Where is the respiratory center?
Therespiratorycenterisawidelydispersedgroupofneuronslocatedbilaterallyinthereticular
substanceofthemedullaoblongataandpons.
18. What influences the respiratory center?
ExcessCO2andhydrogenions(H+)affectrespirationmainlybydirectexcitatoryeffectsontherespi-
ratorycenteritself.Oxygendoesnothaveasignicantdirecteffectontherespiratorycenter.O2acts almostentirelyperipherallyonthecarotidandaorticbodies.
19. What does PEEP mean?
PositiveEnd-ExpiratoryPressureduringmechanicalventilation.PEEPaidsinpreventingalveolarand
smallairwaycollapseandmayhelprecruitlungunitsthatwerepreviouslycollapsed.
20. What are the beneficial effects of PEEP?
• Increasedfunctionalresidualcapacity  • Increasedcompliance  • IncreasedPaO  • Increasedventilation–perfusion(V/Q)ratio(wheninitiallylow)
2
• Decreasedpulmonaryshunt
21. What is the effect of PEEP on cardiac output?
BecauseofincreasedintrathoracicpressureanddecreasedvenousreturnwhenusingPEEP,cardiac
outputmaybedecreased.
22. What are the normal blood gas values?
pH7.40±0.05units (H+)40±5mEq/L
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PCO240±5mmHg
A0.1decreaseinpHcorrespondstoa12mmHgofPCO2increase,whichequalsabasechangeof6mEq/L.  • Goldenruleno.1:ApHof0.08=PaCO2of10mmHg.  • Goldenruleno.2:ApHof0.15=basechangeof10mEq/L.
23. What are the common causes of acid–base disorders?
• Respiratoryalkalosis:hyperventilation,sepsis,anxiety,pain  • Respiratoryacidosis:CNSdepression,neuromusculardisorders,upperandlowerairway
abnormalities
• Metabolicalkalosis:emesis,volumedepletion,nasogastrictube(NGT)drainage,diureticuse,
exogenousalkali,mineralocorticoidexcess
• Metabolicacidosis:ketoacidosis,lacticacidosis,renalfailure,ingestionoftoxins(e.g.,methanol
andpropyleneglycol)
24. How is the diagnosis of respiratory acidosis made?
Respiratoryacidosisisusuallyevidentfromtheclinicalexam,especiallyifrespirationisobviously
depressed.Analysesofarterialbloodgases(ABGs)willconrmthediagnosis.ArterialpHwillbe <7.35,andPCO2willbe>45mmHg.
25. What are some causes of respiratory acidosis?
Anydiseaseorconditionthatmayaffecttherespiratoryfunctioncancauserespiratoryacidosis,
including:
• Chronicobstructivepulmonarydisease(COPD)  • Chestwallorairwayinjury  • Drugeffects  • Pulmonaryedema  • Centralnervoussystem(CNS)depression  • Cardiacarrest  • Extremeobesity(e.g.,pickwickiansyndrome)  • Pneumonia
26. How is the diagnosis of respiratory alkalosis made?
Clinically,respiratoryalkalosisusuallymanifestsashyperventilation.However,dependingonitssever-
ityandacuteness,hyperventilationmaynotbeevident,butananalysisofABGswilldemonstratean arterialpHof>7.45andaPCO2of<35mmHg.
27. What are some causes of respiratory alkalosis?
• Hyperventilation  • Pulmonaryembolus  • CNSinjury  • Excessivemechanicalventilation  • Fever
28. What is Cheyne-Stokes breathing?
Periodsofhyperpnea(deepbreathing)alternatingwithperiodsofapnea.Thecrescendo–decrescendo
patternofbreathingisassociatedwithchangesinPO2andPCO2.Childrenandtheelderlynormally showthispatterninsleep.Innormaladults,causesofthispatternofbreathingincludeheartfailure, uremia,drug-inducedrespiratorydepression,andbraindamage.
29. What are the causes of hypoxemia?
• Lowinspiredoxygenconcentration(lowFiO2):wheninadequateoxygenlevelissuppliedoravail-
able(e.g.,asphyxiation)  • Hypoventilation:inadequateminuteventilation(e.g.,sedationorCNSdepression,brainstemstroke)  • Righttoleftshunt:perfusionwithoutventilation;whenbloodbypassesthepulmonarysystemby
owingfromtherighthearttotheleftwithoutexposuretoinhaledoxygen(e.g.,atrialorventricular
septaldefect,pulmonaryedema,pneumonia)  • Ventilation/perfusionmismatch:Ventilation(V)shouldideallymatchperfusion(Q)atthealveolar-
capillarylevel.Areasofventilationwithoutperfusionaretermeddeadspace(e.g.,pulmonary
embolus).  • Diffusionabnormality:abnormalityofthealveolar-capillarymembranecausinginefcientexchange
ofoxygentothebloodstream(e.g.,diseasesofthelungparenchymaorinterstitium)
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30. What causes stridor?
Stridor,anairwayemergencythatdemandsimmediateattention,iscausedbypartialobstruction
oftheairwayatthelevelofthelarynxortrachea.Thishigh-pitchedbreathsoundcanbenotedon inspirationorexpirationorcanevenbebiphasic.
31. What is the definition of acute respiratory failure?
RespiratoryfailureisaninadequateexchangeofO2andCO2secondarytofailureoftheventilatory
apparatusorgasexchangesystem.Itresultsinhypoventilationand,therefore,hypercapniaand hypoxemia.
32. How is the diagnosis of respiratory failure made?
RespiratoryfailureisprimarilybasedonABGs:hemoglobinsaturationof<92%(whichcorrespondsto
aPaO2of<60mmHg,aPaCO2of>50mmHg,andapHof<7.35[respiratoryacidosis]).
33. How is respiratory failure treated?
SecureandmaintainapatentairwaytodeliverappropriateO2therapyusingmechanicalorsupportive
ventilation.Theairwaymaybeintheformoforalandnasalendotrachealintubation,tracheostomy,or cricothyrotomy.
34. What are the indications for elective intubation and mechanical ventilation?
Theindicationsforintubationandmechanicalventilationarebasedonclinicalandlabvalues.These
include:  • Respiratoryrate>30to40breaths/min  • Negativeinspiratorypressure<25cmH2O  • Vitalcapacity<10to15mL/kgoraPaCO2>50mmHgwithapH<7.3
35. What are the guidelines for withdrawing mechanical ventilatory support (weaning
parameters)?
Mechanicalventilationcanbewithdrawnifoneormoreofthefollowingparametersaremet:  • PaO2>60mmHgwithanFiO2<0.4  • Minuteventilation<10L/min  • PaCO2(35to45)acceptablewithnormalpH  • Respiratoryrate<25breaths/min  • Tidalvolume>4to5mL/kg  • Negativeinspiratorypressure>20cmH2O  • Vitalcapacity>10to15mL/kg
36. What is pleural effusion?
Pleuraleffusionoccurswhenuidaccumulatesinthepleuralspace(i.e.,volumeoverload,infection)
andtheair-lledlungseparatesfromthechestwall.
37. What is atelectasis?
Atelectasisoccurswhenmucusoraforeignobjectobstructsairowinamainstembronchuscausing
collapseoftheaffectedlungtissueintoanairlessstate.Ittypicallyoccurs36hourspostoperatively
andpresentswithmilddyspnea.
38. What chest X-ray findings are noted in a patient with atelectasis?
Radiologicsignsoflobaratelectasiscanbecategorizedasdirectorindirect.Directsignsinclude
increasedopacicationoftheairlesslobeanddisplacementofssures.Indirectsignsinclude
displacementofhilarandcardiomediastinalstructurestowardthesideofcollapse,narrowingofthe
ipsilateralintercostalspaces,elevationoftheipsilateralhemidiaphragm,compensatoryhyperination
andhyperlucencyoftheremainingaeratedlung,andobscurationofthestructuresadjacenttothe
collapsedlung.
39. How is postoperative atelectasis managed?
Treatmentofpostoperativeatelectasisisaimedatexpansionofthelung,and,formostpatients,
incentivespirometryisadequate.However,inpatientswithsevereatelectasis,endotrachealsuction
andevenbronchoscopymaybewarranted.
40. What are the signs of pneumothorax?
Pneumothoraxoccurswhenairleaksintothepleuralspace,causingthelungtorecoilfromthechest
wall.Thesignsofintraoperativepneumothoraxincludeunexplainedhypotension,ventilatoryhypoxiawith
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bulgingdiaphragm,jugularvenousdistention,tympanicthorax,andtracheadeviatedtooneside.Inan
awakepatient,apneumothoraxtypicallypresentswithdyspnea,chestpain,absenceofbreathsounds
ontheaffectedside,andevidenceofpneumothoraxonchestX-ray.Trachealdeviationmaybepresent.
41. What is the appropriate treatment of pneumothorax?
Pneumothoraxisdenitivelytreatedwithplacementofathoracostomytubeconnectedtoclosed
suctionof20cmH2O.However,iftensionpneumothoraxissuspected,immediateneedledecompres-
sionthroughthesecondintercostalspaceinthemidclavicularlineusinga14-gaugeneedleshouldbe
performed.
42. What is the mechanism of bronchial asthma?
Asthmaisachronicdisordercharacterizedbyinammationandincreasedresponsivenessofthe
tracheobronchialtreetodiversestimuliresultinginavaryingdegreeofairwayobstruction.
43. What is the clinical presentation of bronchial acute asthma?
Patientspresentwithdyspneaortachypnea,wheezing,hypoxemia,and,occasionally,hypercapnia.
44. How is bronchial asthma classified?
Oneoftheclassicationsofasthmaisbasedontheseverityandfrequencyofattack(Table17-1).
45. What is the appropriate management of an acute asthma attack?
AnacuteasthmaticattackisbesttreatedbyadministrationofsupplementalO2withaninhaledbeta-
adrenergicagonist(albuterol,3.0mL[2.5mg],in2mLofnormalsalineevery4to6hours,inanebulizer).
Ifthepatientisresistanttobetaagonists,theophyllineshouldbeconsidered.Therapyalsomayinclude
parenteralsteroids,suchasmethylprednisolone(50to250mgover4to6hours).Inasevereasthmatic
attackthatisunresponsivetotheabove,administer0.3mgof1:1000epinephrinesubcutaneously.
46. What clinical information is relevant for patients with COPD to risk-stratify prior to
surgery?
• Smokinghistory:numberofpacksperdaysanddurationinyears  • Clinicalsymptoms:dyspnea,wheezing,cough  • Functionalcapacity:assessmentofmetabolicequivalents(METs).Thosewhocannottolerate>4
METs(i.e.,climbing≥1ightofstairs,walkingonetotwoblocksuphill,golf)areconsidered
increasedrisk.  • Hospitalizations:previousintubations/needformechanicalventilation  • Medications:homeO2therapyandow-rate?Needforsystemicsteroids?  • Infections:anyrecentexacerbations,pulmonaryinfections  • Weightloss:mayberelatedtoend-stagelungdiseaseorcancer
47. What is emphysema?
Emphysemaisaninammatoryresponseinthelungsduetocontinuousexposuretoirritantssuchas
airpollutionandsmoking.Thiscausesnarrowingofsmallairwaysandbreakdownofthelungtissue resultingindestructionofairspaces.Theresultantbrosisresultsinairtrapping(hyperination)and ventilation-perfusionmismatch.Patientscompensatethroughhyperventilationandprolongedexpira­toryperiodstomaintainoxygensaturation>90%(i.e.,pinkpuffer).Physicalexaminationrevealsuse ofaccessorymuscles,hyperinatedlungeldsthatarehyperresonanttopercussion,withdistant, diminishedbreathsounds.
Table 17-1. Classifying the Severity of an Asthma Attack
SEVERITY
Intermittent ≤2/week ≤2/month ≥80% ≤2days/week Mild persistent >2/week 3-4/month ≥80% >2days/week
Moderate
persistent
Severe persistent Continuously Frequent(7/week) <60% ≥2/day
SYMPTOM FREQUENCY
Daily >1/week 60-80% Daily
NIGHTTIME SYMPTOMS
% FEV1 OF PREDICTED
SHORT-ACTING BETA-AGONIST USE
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48. What is chronic bronchitis?
Chronicproductivecoughlastingatleast3monthsoveraminimumof2yearsthatishighlyassoci-
atedwithsmoking.Itischaracterizedbyhypertrophyofbronchialmucinousglands.Thishypertrophy leadstoincreasedthicknessofmucusglandsrelativetooverallbronchialwallthickness(Reidindex increasesto>50%;normalis<40%).Theclinicalsignsareaproductivecough(duetoexcessive mucusproduction)andcyanosis(bluebloaters).Theexcessmucuscausesmucousplugs,trapping carbondioxide,increasingPaCO2,anddecreasingPaO2,resultinginanincreasedriskofinfectionand corpulmonale.
49. What is bronchiectasis?
Bronchiectasisisaconditioninwhichthebronchiareabnormallyandirreversiblydilateddueto
destructionofthemuscleandelasticityofthelungparenchymasecondarytoinammation.The disordercanbeassociatedwithcongenitallungdiseasesortheresultofavarietyofpulmonary insultsincludingaspirationorsevereinfection.Theresultantdilationanddestructioncausesthelung toinadequatelyclearsecretionsandbecomecolonizedwithpathogenicbacteria,resultinginrecurrent pulmonaryinfections.
50. What is adult respiratory distress syndrome (ARDS)?
ARDSisaC5a-inducedneutrophilaggregationinthelung.Thisaggregationisoneofthemajor
mechanismsofpathologyofARDS.Thedamagedcapillariesleakprotein-richuidintotheintersti­tium,whichleadstochangesinpulmonaryfunction.
51. What causes ARDS?
ARDSusuallyresultsfromaninjurytothealveolar-capillarymembrane.Italsocanbecausedby
anexistingunderlyingdisease,suchassystemicsepsis,fatembolism,headinjury,aspiration, pancreatitis,orinhalationinjury.Patientstypicallyshowseveredyspneaandhypoxemiarefractoryto supplementalO2withdiffusepulmonaryinltratesonchestradiograph.
52. What is the appropriate management of ARDS?
ManagementofARDSincludesimmediatetransfertoanintensivecareunitandplacementofa
pulmonaryarterycatheterwithmechanicalventilationtomaintainthepulseoximetry(SpO2)>90%, whichcorrespondstoPO2>60mmHg.Inaddition,thepulmonarycapillarypressureshouldbekeptin therangeof12to15mmHg,andthecardiacindexshouldbemaintainedabove3L/min/m2.Treat­mentofARDSisgenerallysupportivetoachieveO2saturationof90%whileminimizingbarotrauma andoxygentoxicity.
53. What are the features of ARDS?
• Historyofmajorinsult  • Increasedrespiratorydistress  • DiffuseinltrationonchestX-ray  • Hypoxemia(PaO2<60mmHgwithFiO2>0.6)  • Respiratoryalkalosis  • Normalpulmonarycapillarywedgepressure(PCWP)  • Decreasedpulmonarycompliance  • Increasedshuntfunction  • Increaseddeadspaceandventilation
54. How often does aspiration occur, and what are the complications?
Aspirationisarelativelyrareoccurrenceaffectingapproximately1outofevery10,000patients
undergoinggeneralanesthesia.Intheoutpatientsetting,deepsedationwithoutasecureairwayhas alsobeenshowntobesafewithoutasignicantincreasedriskforaspiration.Complicationsinclude bronchospasm,pneumonitis,pneumonia,acuterespiratorydistresssyndrome,lungabscess,and empyemaconferringanincreasedriskofmortality.
55. What are common risk factors for aspiration?
• InadequateNPOstatus(emergentcases)orfailuretofollowNPOguidelinesforanesthesia  • Extremesofage(twiceascommoninchildrenandelderly)  • Medicationsthatdecreaselevelofconsciousness(sedative/hypnotics/anxiolytics)andbluntprotec-
tivereexes  • Headtrauma  • Stroke
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• Presenceofanasogastrictube  • Prolongedsupineposition
56. What is the appropriate management of aspiration?
Abaselinechestradiographshouldbeobtainedforanypatientsuspectedofaspiration.Afterimme-
diatesuctioning,supportivecareisthemainstayoftreatmentandincludessupplementaloxygen andmonitoringofoxygensaturationinaninpatientsetting.Ventilatorysupportshouldbeinitiated ifconcernforrespiratoryfailurearises(seequestion12above).Antibioticsshouldnotbeinitiated unlesstheeventleadstopneumoniaandculturescanbetailoredtotargetspecicorganisms. Classically,aspiratedmaterialconsistsofgram-negativeoranaerobicorganisms(oral/gastroin­testinalora).Aspirationofgastriccontentscanleadtochemicalpneumonitisandalsorequires supportivecare.
57. How can aspiration risk be decreased?
Byrecognizingsurgicalpatientswhoarehighrisk,adjunctivestepsandmedicationcanbetakento
minimizetheoverallrisk.Adheringtostandardfastingprotocolspriortoanyprocedurewilloptimize gastricemptying.Gastricacidscanbeneutralizedwithantacidsorhistaminereceptorantagonists. Logically,pro-motilityagentssuchasmetoclopramidewillaidingastricemptying;however,nodata supportsthis.Aspirationcanbepreventedincriticallyillpatientsbymaintainingthehead-of-bed ≥30degrees,minimizingsedatives,andavoidingbolusfeedsinhigh-riskpatients.
58. What drugs interfere (interact) with aminophylline?
Themostcommonlyciteddrugiserythromycin,whichincreasesserumlevelsofaminophylline.
Cimetidinealsoincreasesserumlevelsofaminophylline.
59. What are the signs and symptoms of pulmonary embolism (PE)?
PEcanpresentwithacuteonsetofpleuriticchestpain,dyspnea,syncope,orlegpainandswelling.
Manypatientsmayhavenosymptoms.SignsofaPEincludetachypnea,hypoxemia,rales,unex­plainedtachycardia,elevatedjugularvenouspressure,andlow-gradefever.RiskfactorsforPEinclude stasis(immobility,obesity),recentendothelialinjury(trauma,surgery,recentfracture,anddeepvein thrombosis),andhypercoagulablestate(pregnancy,oralcontraceptiveuse,malignancy).
60. How is the pre-test probability of deep vein thrombosis (DVT) determined?
TheWell’scriteriaisamethodofdeterminingthelikelihoodofDVT.Itisbasedonmajorandminor
criteria.Majorcriteriaincludeactivecancer,immobilization,bedrest>3days,majorsurgerywithin 4weeks,swellingofthethighandcalf,familyhistoryofDVT.Minorcriteriaincluderecenttraumato symptomaticextremitywithin60days,pittingedema,dilatedsupercialveins,erythema,andrecent hospitalizationwithin6months.Ifmorethanthreemajorcriteriaortwomajorandtwominorcriteria aremet,thenthereisahighlikelihoodthatDVT/PEcanbepresent(∼85%+DVT).
61. How is PE diagnosed?
ImmediateABG,electrocardiogram(ECG),andchestX-rayshouldbeobtained.TheABGwill
revealhypoxemia,hypocapnia,andrespiratoryalkalosiswithanincreasedA–agradient.AnECG mayrevealsinustachycardiaoratrialbrillationwithsignsofrightventricularstrain(e.g.,right bundlebranchblockwitht-waveinversionsinleadsV1-V4).ChestX-raymayshowatelectasis, effusion,andaraiseddiaphragm.WithalargePE,thechestX-raymayhaveaHamptom’shump,a wedge-shapeddensityabuttingthepleura,orWestermarksign,whichsharplycutsoffofavessel distaltotheembolus.D-dimerlevelscanbeassessedwithhighsensitivitybutpoorspecicity.If thepatientisexperiencinganyasymmetricswellinginanyextremity,thenDVTshouldberuled outwithanultrasound.BypassingtheselaboratorytestsandobtainingCTangiographymaybe warranted.
62. What is the appropriate management of postoperative PE?
Oncethepatienthasbeenstabilized,treatmentincludesacuteanticoagulationwithintravenousor
subcutaneousheparinoralowmolecularweightheparin.Ifgivenintravenously,heparinshouldbe titratedtoagoalPTTof60to85seconds.Oncesuitableacuteanticoagulationhasoccurredand PTTistherapeutic,thepatientistransitionedtoanticoagulationwithwarfarin(goalINRof2to3for 3to6monthspostevent).Withacontraindicationforanticoagulation,aninferiorvenacavalter shouldbeplaced.ForlargeproximalPEwithhemodynamiccompromise,thrombectomymaybe considered.
CHAPTER 17 RESPIRATORYDISORDERS 191
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