Andersons pediatric cardiology 325

“pulmonaryhypertension”willbeusedasasurrogateforelevatedpulmonary
vascularresistanceintheabsenceofanatomiccommunicationsbetweenthe
ventriclesand/orgreatvessels.Itisnowrecognizedthatprematureinfantsmay
sufferfromacutepulmonaryhypertensionandthatpulmonaryvasculardisease
increasesmorbidityandmortalityassociatedwithchroniclungdisease(Table
15.7).Itisimportanttomakeadistinctionbetweenreversibleandirreversible
causesbecausetheresponsivenesstopulmonaryvasodilatoragentsdependson
thedegreeofpulmonaryvascularremodeling.Factorscontributingtopulmonary
remodelingincludehypoplasiaduetoprolongedruptureofmembranesorrenal
agenesis.
Table15.7
CausesofPulmonaryHypertensioninPrematureInfants
Acute
Reversible
Respiratorydistresssyndrome
Pneumothorax
Sepsis
Irreversible
Pulmonaryhypoplasia
Congenitaldiaphragmatichernia

Chronic,WithVariableReversibility
Chroniclungdisease
Chronicpatencyofarterialductorotherleft-to-rightshuntlesions
Congenitallymalformedheart
Mildpulmonaryhypoplasia

AcutePulmonaryHypertension
Persistentpulmonaryhypertensionofthenewbornisdefinedasthefailureof
normalpostnatalfallinpulmonaryvascularresistancetoasufficientdegreeto
facilitateanadequateriseinpulmonarybloodflowforoxygenation,regardless

ofabsolutepulmonaryarterypressure.222Theincidenceisnotclearlydescribed,
althoughahigherfrequencythanintermneonateshasbeenreported.223The
regulationofpulmonaryvascularresistancerepresentsabalancebetween
vasoconstrictorandvasodilatoragentsandthebiochemicalprocessesintegralto
transitionaredevelopmentallyregulated,whichmaymakepreterminfantsat
greaterrisk.224Inaddition,preterminfantsaremorefrequentlyaffectedbylung
parenchymaldisease,whichimpactsontheadequacyofrecruitmentand
oxygenation,bothofwhichmaymodifypulmonarybloodflow.Theclinical
consequencesofacutepulmonaryhypertensionincludeoxygenationfailureand
poorsystemicbloodflow,whichmayleadtohypotensionrelatedtoright
ventricularfailureand/orpulmonary-to-systemicshunting.225Earlyonsetacute


pulmonaryhypertensionmaybeassociatedwithincreasedriskofchroniclung
disease,particularlyinthosewithpulmonaryhypoplasia,226andthemortality
rateforpreterminfantswithpulmonaryhypertension,at26.2%,issixtimes
higherthanmatchedcontrols.223

DiagnosisofPulmonaryHypertensionin
PrematureInfants
Thediagnosisofpulmonaryhypertensioninprematureinfantsischallenging,
particularlyinthepresenceoflungdisease.Thesignsandsymptomsof
pulmonaryhypertensionarenonspecific.Agradientbetweenpreductaland
postductaloxygensaturationmaybehelpful,ifpresent;however,itiscommonly
absentinthepresenceofasmallorabsentductusarteriosusorabidirectional
shuntattheductallevel,andthereforetheabsenceofagradientdoesnotruleout
acutepulmonaryhypertensionasadiagnosis.Theelectrocardiogrammayreveal
featuresofpulmonaryhypertension,suchastallPwavesandevidenceofright
ventricularhypertrophy.Cross-sectionalechocardiographyisthegoldstandard
becausecardiaccatheterizationisrarelyperformedandmaybepoorlytolerated.

Theestimationofrightventricularsystolicpressurefromthevelocityofthe
tricuspidregurgitantjetmayunderestimatethetruepulmonaryarterypressurein
thepresenceofsignificantrightventriculardysfunction.227Assessmentofseptal
curvaturemaybeused;however,thepresenceofapatentductandtransductal
shuntingallowsmoreaccuratequantificationofpulmonaryarterialpressure.228

EchocardiographyforIdentificationof
ComplicationsofPulmonaryHypertension
Echocardiographicassessmentofventricularperformancemaybevaluable,
particularlyonserialexaminations,becausetherightventricleisuniquely
vulnerabletoafterloadandmaytoleratepulmonaryhypertensionpoorly.229,230
Similarly,thereisevidenceintermneonatesthatpulmonaryhypertensionis
associatedwithleftventriculardysfunction,231whichmayrelatetoreduced
preload,abnormalconformation,ventricular-ventricularinteraction,orimpaired
coronaryoxygendelivery.Therearelimited,butincreasing,referencerangesfor
measuresofmyocardialperformanceinpretermneonates.


TreatmentofAcutePulmonaryHypertension
Themanagementofpretermneonateswithacutepulmonaryhypertensionis
basedonthreeprinciples.First,itisessentialthatmodifiablefactorscontributing
topulmonaryvasoconstrictionbecorrected.Second,pulmonaryvasodilator
therapyshouldbeconsidered.Finally,supportivetreatmentofcardiovascular
complicationssuchasrightventriculardysfunctionandpoorsystemicblood
flowshouldbeinstituted.
RespiratoryManagement.
Theprimarytreatmentistheadministrationofoxygenonthebasisthat
hypoxemialeadstoworseningofthepulmonaryhypertension.Oxygenisa
potentpulmonaryvasodilator,althoughanimalexperimentalmodelsdemonstrate
minimalintervalreductioninpulmonaryvascularresistanceaboveapartial

pressureofoxygenof50mmHg232;thisrelationshipmaybebluntedin
prematureinfants.233,234Hyperoxiacontributestothedevelopmentofoxygen
freeradicalsthatmaybepoorlyscavenged235,236andareassociatedwith
pulmonaryvasoconstriction.237Thereremainsuncertaintyandcontroversy
regardingthemostdesirablesaturationforprematureinfants.Thereissome
justificationformaintainingsaturationsgreaterthan93%,238andsome
randomizedcontrolledtrialssuggestimprovedmortalityathigheroxygentarget
saturations.239Thegoalofassistedmechanicalventilationistooptimize
clearanceofcarbondioxideandlungrecruitment.Bothventilationlessthan
functionalresidualcapacity240andoverdistensionhavebeenassociatedwith
increasedpulmonaryvascularresistance241andimpairedpulmonaryblood
flow.242Surfactanttherapyisassociatedwithimprovedcomplianceandmay
reducepulmonaryvascularresistance243;however,repeatdosingmayimpair
alveolaroxygenationandshouldbeconsideredthoughtfully(Fig.15.12).