Andersons pediatric cardiology 1828

superiorcavopulmonaryconnectionandincreasesagainaftertheFontan
operation.Pulmonaryarterypressureandventricularend-diastolicpressurefall
throughout.Inadditiontothisserialhemodynamicdatainarelativelysmall
cohort,cross-sectionalquantitativecatheterizationdatainlargersubsetsof
patientshaveconfirmednearlyidenticalvaluesforventricularoutputaswellas
atrialandpulmonaryarterypressuresateachstage.51,66–69

UnanticipatedHypoxemia(Fig.70.5,Table70.4)
Unanticipatedhypoxemiaduringandafterstagedreconstruction(beyondthe
typicalexpectedvaluesshowninFig.70.5A)maybeduetomanycausesrelated
tovariouscombinationsofcardiacdysfunction,pulmonarydysfunction,andthe
statusofthesurgicalprocedures.Despitetheproteanandmultiplecausesinthe
differentialdiagnosisofunanticipatedhypoxemia,theetiologymaybe
summarizedinthreebroadcategories:lowmixedvenoussaturation(seeFig.
70.5B),lowpulmonaryvenoussaturation(seeFig.70.5C),anddecreased
pulmonarybloodflow(seeFig.70.5D).Thesefactorsmayoccurinisolationor
combinationandaresummarizedinFig.70.6.

FIG.70.5 Schematicrepresentationofcategoricaletiologiesof
unexplained,atypicalhypoxemiaduringandfollowingstaged
reconstruction.Thenormalarteriovenousdifferenceinoxygensaturations
(A-VD02)isassumedtobebetween20%and30%.Valuesinthecircles
representpotentialvenousoxygensaturations;valuesintheboxes
representapproximatearterialoxygensaturations.(A)Typicalvalues


duringstagedreconstruction.Lowerthanexpectedarterialoxygenation
maybeexplainedtotallyorinpartbyalowmixedvenousoxygen
saturation(B),lowpulmonaryvenousoxygensaturation(C),and/or
decreasedpulmonarybloodflow(D).Specificcausesareaddressedin
Table70.5.*FollowingtheFontanoperation,therewillbevariablearterial

hypoxemiadependingonanyresidualright-to-leftshunting(e.g.,
fenestration).

Table70.4
TypicalPhysiologicChangesDuringStagedReconstruction(Fontan
Pathway)
HemodynamicVariable
Systemicbloodflow(L/minperm2)
Aorticoxygensaturation
Mixedvenousoxygensaturation
Pulmonarybloodflow(L/minperm2)
Pulmonary-to-systemicflowratio
(Qp:Qs)
Ventricularoutput(L/minperm2)
Pulmonaryarterypressure
Ventricularend-diastolicpressure

PriortoSCPC(n=
65)
2.8±0.8
78±6%
49±7%
3.8±1.3
1.4±0.6

PriortoTCPC(n=
65)
3.3±1.0%
85±5%
64±6%

2.6±1.2
0.7±0.3

AfterTCPC(n=
42)
3.0±0.8%
91±6%
64±8%
2.7±0.6
0.95±0.2

6.6±1.1
14±5
9±3

3.3±1.0
11±3
8±3

3.0±0.8
10±2
6±3

Qp,pulmonarybloodflow;Qs,systemicbloodflow;SCPC,superiorcavopulmonaryconnection;
TCPC,totalcavopulmonaryconnection.Serialchangesinpatientsfollowingstagedreconstruction
reportedbyCohenetal.65Additionalstudieshaveconfirmedthesegeneralvaluesindifferent
patientpopulations.51,66–69


FIG.70.6 Differentialdiagnosisofhypoxemiaacrossthesurgical

continuum.aThesefactorswillonlycontributetohypoxemiaafteraFontan
procedureifthereisananatomicrighttoleftshunt,suchasafenestration,
baffleleak,ordecompressingvenouscollateral.

VenovenousCollaterals
FollowingtheSCPC,pressureintheuppervenouscompartmentandpulmonary
arteriesishigherthanthatinthelowervenouscompartment,pulmonaryveins,
andatrium.Becauseofthispressuregradient,previouslysmallvenouschannels
maydilateandprogressivelydirectbloodawayfromthehigher-pressurecircuit
intothelower-pressurecircuit(Fig.70.7).Thephysiologiceffectofthese
connectionsistoreduceflowinthesuperiorcavalveinandthereforetotal
pulmonarybloodflow,resultinginunanticipatedhypoxemia.Thesevenovenous
collateralsaremoreprevalentandhemodynamicallysignificantinthefaceofa
largervenouspressuregradientfromtheupperbodytothelowerbody,asin
patientswithelevatedPVR,pulmonaryarteryhypoplasia,orananatomically
narrowsuperiorcavopulmonaryconnection.70–72Themostcommonlocations
forthesevenousstructureswerepreviouslydescribedbyMcElhinneyand
colleagues.72a,73Thehypoxemiamayberelievedbycoilordeviceembolization
duringcardiaccatheterization(seeFig.70.7;Videos70.1to70.5).Althoughless
common,thesevenovenouscollateralsmaybeseenaftertheFontanprocedure
aswell.73–75