Andersons pediatric cardiology 1827

Duringstagedreconstruction,perhapsthemostabruptphysiologicchangetothe
circulationoccursimmediatelyafterthesuperiorcavopulmonaryconnection
(SCPC)orbidirectionalGlenn.Priortotheprocedure,thefUVHdistributes
pulmonarybloodflow(Qp),systemicbloodflow(Qs),and,ifpresent,the
regurgitantvolume(Qr).Immediatelyaftertheprocedure,moststudiesreport
thatventricularvolumedecreasessignificantly(onlyQs+Qr)whereasmass
doesnot(Fig.70.3),althoughtheseresultshavebeenvariabledependingon
ventricularmorphology,age,andotherfactors.Thisresultsinanacutemass-tovolumemismatchandtransientlymildlydecreasedventricularfunction.49–53In
addition,theupperbodyhasanacuteelevationincentralvenouspressure,andit
hasbeenspeculatedthatthisacutechangeinvenouspressureresultsinincreased
intracranialpressure(similartowhatisseenintraumaticbraininjury)toexplain
thetransientirritabilityandCushingresponse—systemichypertensionand
relativebradycardia—sofrequentlyseenfollowingthisprocedure.

FIG.70.3 Schematicrepresentationofthechangesinthemass-tovolumeratioimmediatelyfollowingthesuperiorcavopulmonaryconnection.
Immediatelyaftersurgery,ventricularmassisunchangedwhileventricular
volumeisdecreased.

Ingeneral,arterialflowtotheupperbodyaccountsfor40%to60%ofthe
ventricularoutput.FollowingthebidirectionalGlenn,thepulmonarybloodflow
isessentiallyobligate;thatis,intheabsenceofdecompressingvenovenous
collaterals(discussedfurtheron),theupperbody'sarterialflowtothebrain,
neck,andarmsmustreturntothepulmonaryarteriesthroughthesuperiorcaval
vein(Fig.70.4).Thesuperiorcavopulmonaryconnectioncoupledwiththe
eliminationofothersourcesofpulmonarybloodflowresultsinanimmediate


decreaseinventricularworkandventricularstrokevolumeby30%to60%.The
physiologicbenefitsofthisstepinsurgicalmanagementareapparentwithin
weeksofsurgery,asmostbabiesexperienceaconsiderableclinicalimprovement
ingrowthanddevelopment.Analternativestrategyistoleaveanadditional

sourceofpulmonarybloodflow(shunt,antegradeflow,etc.)inadditiontothe
superiorcavopulmonaryconnection.Theadvantagesofthisstrategyare
improvedpulmonaryarterygrowth,higheroxygensaturations,andacontinued
supplyof“hepaticfactor”tothepulmonaryvascularbed.Disadvantagesinclude
persistentvolumeloadingofthefUVHand,inmoststudies,alongerhospital
lengthofstayandahigherincidenceofpleuraleffusionsandchylothorax.54–57

FIG.70.4 Schematicrepresentationofupperbodyflowfollowingthe
superiorcavopulmonaryconnection.Thearrowsrepresentdirectionof
bloodflow.Intheabsenceofvenouscollateralsfromtheupperbodytothe
lowerbody(decompressingvenovenouscollaterals),thepulmonaryblood
flowisidenticaltothebrachiocephalicoutflowfromtheheart,or
approximately50%to60%ofthecardiacoutputinaninfant.

Importantly,itisatthisstageofstagedreconstruction,aswellasbetweenthe
GlennandFontan,thatadditionalprocedures,ifnecessary,aremostsafely


performed.Theseincludecardiacprocedures(e.g.,pulmonaryarterioplasty,
atrioventricularvalvuloplasty)andnoncardiacsurgery(e.g.,gastrointestinal,
facial,orthopedic,andotherprocedures—seealsoChapter90).51,58–60

TotalCavopulmonaryConnection(Fontan
Procedure)
FollowingthebidirectionalGlennprocedure,lower-bodyvenousreturnenters
thefUVHinanunobstructedmanner,thusmaintainingadequateventricular
preloadwithlowvenouspressureinthelowerhalfofthebody.However,
followingtheFontanprocedure,whichseparatesthesystemicandpulmonary
circulations,boththelower-andupper-bodyvenousreturnmusttravelthrough
multiplepotentialresistorstoflow,asshowninFig.70.1.Althoughsystemic

oxygenationimproves,themultipleresistorstosystemicvenousreturnresultin
increasedpressureinboththesuperiorandinferiorcavalveinsaswellasinthe
pulmonaryarteries.Studieshavealsoshownthat,bothacutelyandchronically,
thefUVHischronicallypreload-deficient,andcardiacoutputfallsslightly
comparedwiththepreoperativestate(seefurtheron).Thechronicallyelevated
centralvenouspressureisthoughttobeprimarilyresponsibleforthemajorityof
long-termconsequencesoftheFontancirculation,particularlyfortheliver,lung,
intestine,andlymphaticsystem.22–24,26,61–64Theseconsequencesarediscussed
indetailinChapter73.

SerialPhysiologicDataDuringStaged
Reconstruction
Thehemodynamicconsequencesoftheanatomy,physiology,andsurgical
interventionshavebeenqualitativelydescribedbyechocardiographyand
quantitativelybycardiaccatheterizationandmagneticresonanceimaging.
Cohenandcolleagues65reportedserialdataon65patientsundergoingcardiac
catheterizationbeforethesuperiorandtotalcavopulmonaryconnectionsaswell
asduringlatefollow-up(seeTable70.4).Insummary,thereisafallinboth
ventricularoutputandsystemicbloodflowthatismostpronouncedwiththe
GlennprocedurebutcontinuesaftertheFontanprocedure.Thearterialand
venousoxygensaturationisnarrowest(highestoxygendelivery)followingthe
GlennandbeforetheFontan.Pulmonarybloodflowisreducedfollowingthe