Andersons pediatric cardiology 375
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antiapoptosis.404
PostoperativehyperthermiaiscommonafterCPB405andhasbeenassociated
withpoorerneurologicoutcome.406,407Attentiontothecontroloftemperature
duringrewarmingandimmediatelyfollowingbypasscanreducetheincidenceof
undesiredhyperthermia.Limitingthearterialoutflowbloodtemperaturefrom
thebypasscircuitto37°Cisrecommended.408Inductionofpostoperative
hypothermiashouldbestronglyconsideredforpatientsexperiencing
uncontrolledorprolongedperioperativeischemia.409Hypothermiamayafford
protectionindependentofitseffectsoncerebralbloodflowandmetabolism.The
effectsofhypothermiapostinjuryarelikelyduetoreductioninapoptoticcell
deathandthusbothintraoperativeandpostoperativehypothermiamayprovide
antiapoptoticprogramming.Reductioninapoptoticcelldeathhasbeen
demonstratedusingcerebralperfusionasasupportivestrategyasopposedto
hypothermiccirculatoryarrest.324,325Postoperativemildhypothermiaand
administrationofalbuminaresimpleclinicalinterventionscommonlyapplied
thatmayalteroutcomeafterincompleteischemia.285,410Evidenceoffocal
ischemiafromgasembolismorothercausesshouldpromptconsiderationof
hyperbarictreatmentwithoxygen.411,412
Monitoring
Becausearangeofconditionscanaffectcentralhemodynamics,regional
cerebralperfusion,cerebralmetabolism,andflowmetabolismcouplingduring
cardiacsurgery,cerebraloxygenationislikelyalteredinbothpredictableand
unpredictableways.Cerebralhypoxia,measuredbyjugularvenoussaturationor
NIRS,hasbeenshownexperimentallytoberelatedtoinjuryduring
ischemia204,413withsimilarfindingsreportedinhumans.396,414Hypoxicischemicconditionscannotreliablybeidentifiedbystandardhemodynamic
monitoring.Becauseaggressivepreventionofovertandocculthypoperfusion
improvesoutcomes,190,351,415measurementofglobalandregionaloxygenation
isrecommendedasamethodtopreventandtreatunanticipatedand
unappreciatedhypoxic-ischemicconditions.Thisisespeciallycrucialinthe
immediateperioperativeperiodwheninterventiontoimproveoutcomeis
possible.415–417
IntraoperativeEchocardiography
Transesophagealechocardiographyhasbecomeamainstayofintraoperative
managementofthepatientundergoingcardiacsurgery.Specificguidelineshave
beendevelopedastotheindicationsforitsuseinchildren.Thereisgeneral
agreementthatthetechniqueisindicatedineverychildover3kg.Somecenters
usethesysteminanyinfantover2.5kginwhomaprobeiseasilyplaced.An
echoisgenerallyperformedatthebeginningofeverycase,bothtoconfirmthe
anatomypreviouslydetectedbyusingtransthoracicwindowsandtoobtainrealtimeorientationtodynamicstructures.Intraoperatively,echocardiographycan
beimportanttoverifythatairhasbeenclearedfromcardiacchamberspriorto
allowingcardiaccontractionsandemergencefromcardiopulmonarysupport.It
canalsobeveryusefulindelineatingthesourceoffailurewhenachildisnot
abletobeweanedfrombypass(i.e.,residuallesions).Forinstance,
echocardiographyisveryusefulwhendifferentiatinghypovolemiafrom
functionalcompromiseandresidualstructuraldeficits.Attheterminationofthe
procedure,echocardiographyiscriticalinverifyingtheadequacyofmany
repairs.418
PostoperativeExtracorporealSupport
Short-termmechanicalsupportisoccasionallynecessaryfollowingcomplex
cardiacoperations.Theuseofextracorporealmembraneoxygenation(ECMO)
carriesareasonableexpectationofrecoveryforsmallpatientsin
cardiopulmonaryfailure.Inthecurrentera,thetechniqueisanessential
componentofprogramsundertakingcomplexcongenitalcardiacsurgery.419,420
Thecircuitusedbymostcentersisadirectdescendantofthecircuitinitially
developedforsupportoftheneonatewithpulmonaryhypertensionandpersistent
fetalcirculationandhastheadvantageofbeingstandardizedandwell
understoodbythespeciallytrainedstaffwhomanagethecircuit.421,422Keytoits
successwasthedevelopmentofthesiliconemembraneoxygenator,which
extendedthesafedurationofextracorporealsupportfromhourstodays,
providingenoughtimeforrecoveryofmostneonateswithrespiratoryfailure.
Siliconemembraneswerefollowedbyhollowfibermembraneoxygenatorsand
boththeoxygenatorandthecircuitcanbeheparinbonded.423Asaresultthe
requirementforheparinisreduced,whichcanbehelpfulincontrollingbleeding.
Morerecently,polymethylpentenemembraneoxygenatorshavebeendeveloped
thatallbuteliminateissueswithplasmaleakageassociatedwiththehollowfiber
membrane.Thisadvantageallowsforlonger-termuseofanoxygenatorwithout
theneedtoexchangeitduetodecreasedgasexchange.424ECMOisstillofvalue
onlyintheshortterm,butbecausemyocardialdysfunctionislikelytorecover
within96hours,thisdurationofsupportissuitableforthepostoperativepatient.
Survivaltodischargefromhospitalforpatientswhorequiredextracorporeal
supportsubsequenttotheoperationisintherangeof40%.425,426Not
surprisingly,amongpatientsrequiringsuchsupport,alackofresiduallesions
favorssurvival.426Patientswithafunctionallyuniventricularcirculation
sufferingacutethrombosisofashuntarenoteworthyforahighrateof
survival.426Intheearly2000s,manycentersdevelopedarapidresponsesystem
topermitrapidcannulationtosalvagepatientswhosustainedunexpectedcardiac
arrest.427MorerecentlyandasapartofcardiopulmonaryresuscitationtoECMO
processesandprotocols,ECMOcircuitsaremaintainedfortheemergent
initiationofECMO.Thetechnique,however,isstillsuitableonlyforrelatively
shortperiodsoftreatment.Bridgingtotransplantationrequireslong-term,lowmorbiditysupport.
Centrifugalpumpshaverecentlybeenputtousesupportingpatientswith
isolatedcardiacdysfunctionrequiringtemporarysupport.TheThoratec
Centrimag428–430andPedimag431(Thoratec)andtheMaquetRotaflow432
(GetingeGroup)havebeenusedinpatientswithbothbiventricularandsingle
ventriclecirculation.
Providingmechanicalsupportforthefailingheartoverlongerperiodshas
becomeaclinicalrealityinadults,andpermitsbothsupportofthecirculationas
wellastheopportunityforrehabilitationanddecreaseinpulmonaryvascular
resistance.Inchildren,long-termsupportismorechallengingduetochallenges
ofsmallsizeandcongenitalheartdiseaseanatomy.TheBerlinHeart(Berlin
HeartAG)isaparacorporealpneumaticdisplacementpumpwithchambersand
cannulasspecificallydesignedforpediatricuseanditwasapprovedinthe
UnitedStatesin2011.Thepumpingventricleisavailableinavarietyofsizes
from10to80mL.Thesmallestsizeissuitableforsupportofinfants(Fig.
16.15).433Becauseoftheparacorporealorexternalpositionofthepumpandthe
rangeofavailablecannulas,thedeviceaccommodatesarangeofanatomic
variances.Itisevenpossibletosupportpatientswithfunctionallyuniventricular
circulations.434,435Thrombuswithinthedevicecanbeidentifiedbyvisual
inspectionandtheexternalpositionpermitschangingofthepumpwithout
reoperation.ThedownsideoftheBerlinHeartisthehighrateofembolicstroke,
upto29%,butrecentexperiencewiththeuseofbivalirudinispromisingand
