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DeterminantsofNeonatalCardiacOutput
FjayFrickerMDNeonatologybasiccorecurriculum
DeterminantsofcardiacoutputintheNeonate
DifferencesbetweenFetalandadultMyocardium
Organizationandthenumberofmyofbrilsundergochangesduringdevelopment.§ Orientationofmyofibrils§ Non-contractileelements
DeterminantsofNeonatalCardiacOutput
FetalvsAdultMyocardium• ActiveTensionlowerthanadultatsamefiberlength(SystolicFunction)
• RestingtensiongreaterinFetusthanadult(Diastolicfunction)
• Sarcomeral lengthnotdifferent• Cannotbeexplainedbygreaterproportionofnoncontractileelements
• ?DifferentsensitivityoffetalcontractileproteinstocytosolicCalcium
DeterminantofCardiacOutputFetusVsadultAfterload
StarlingCurveConceptofDescendingLimb
DeterminantsofCardiacOutputTheSarcomere
DeterminantsofCardiacOutputTheSarcomere
DeterminantsofFetalCardiacoutput
MajorfactorsdeterminingCardiacOutput
• HeartRate• Preload• Afterload• Contractility
HeartRateandStrokeVolumeHeartRateNeonateCardiacoutputmoredependentonHeartRate80-180bpm
PressureVolumeLoopTheModel
PressureVolumeLoopInterpretation
PressureVolumeloop
DeterminantsofCardiacOutputIncreaseinAfterLoad
DeterminantsofNeonatalcardiacOutput
Anrep EffectSuddenincreaseinafterloadontheheartcausesanincreaseinventricularinotropy.ThisPhenomenonisobservedindenervated hearts,isolatedmuscleandinintacthearts.Significanceisthattheincreasedinotropycompendates fortheincreasedendd-systolicvolumeanddecreasedstrokevolumecasusedbyincreaseinafterload.
HeartFailureDefinition
• “..Heartfailureisaclinicalsyndromeinwhichheartdiseasereducescardiacoutput,increasesvenus pressures,andisaccompaniedbymolecularabnormalitiesthatcauseprogressivedeteriorationofthefailingheartandprematuremyocardialcelldeath”ARNOLDKATTZ
• Or• “TheHeartisunabletomeetthemetabolicdemandsofthe
body”
HeartFailureCompensatoryChanges
HeartFailure
EffectiveArterialBloodVolume
RenalVasoconstrictionReninAngiotensionAxis
NaandH2ORetension Reninrelease
Angiotension II
HeartFailureConceptofforwardorbackwardfailure
Increasedintravascularvolume
IncreaseintheEnd-DiastolicPressureLVandRV
IncreaseinSystemicandPulmonaryVenousPressure
Hepatomegaly,Pulmonaryedemaandedema
HeartFailure
RegionalCirculationSympatheticNervousAngiotensionIIsystem
Vasoconstriction
NAandH2OcontentofBloodvessels
HeartFailureConcept
“BackwardorForwardFailure”
LiverCongestion/PulmonaryedemaRenalPerfusion
NaandH2O
IntravascularVolume RVEDPLVEDP LiverenlargementPulmonaryedema
InotropesinNeonates
Inotropes• Chosenaccordingtophysiologyandtitratedtoagoalto
beachieved• Combinationofdrugsismoreoftenusedtopreventside
effects• OtherfactorsaffectingCO:
– Acid-baseandelectrolytebalance(ex:acidosis,hypoCa)– Cardiopulmonaryinteractions(ex:ventilation)– Hypoxemia(ex:HIE,PH)– Presenceofintraorextracardiacshunts(ex:ASD,PDA)– Neuro-humoralresponse(ex:adrenal,thyroid,glucose)– Oxygencarryingcapacity(CaO2),OxygenConsumption(VO2=
metabolicdemands)– DysrhythmiasandlostofAVsynchrony– Patophysiology(Biventricularvs.SV)
Nicholz,HeartDiseaseinInfantsandChildren
Ruoss,McPhersonandDiNardo,Neoreviews,2015
Dopamine• Endogenouscatecholamineprecursorofnorepinephrineandepinephrine
• Receptors:alpha,beta,dopamine• Dosedependent:
– 0.5-2mcg/kg/min:dopaminergic recept (nobenefit)– 2-10mcg/kg/min:Beta1recept (éCOandSBP)– >10mcg/kg/min:alpharecept (vasoconstr,éSBPandDBP)
• UndesiredCVeffects:– oxygenconsumptionofmyocardium– automaticity(arrhythmias),tachycardia– 1pediatricstudy:associatedwithincreasedmortality- Venturaetal,PCCM2015
• Non-CVeffects:– Prolactin,thyrotropinandgrowth-hormonesecretionsuppression– Extravazation
Osborn, Evans,Kluckow,Neoreviews2004Ruoss,McPherson andDiNardo,Neoreviews,2015
Dobutamine• Syntheticcatecholamine:doesnotreleaseNE• Receptors:beta1myocardium(é contractility)andB2peripheral(vasodil)
• UsedinmanyHIEstudies(êcontractility-LCOS)• Doses:
– >10mcg/kg/min:éCOandHR -Devictoretal.,ArchFrPed,1988
– 5-7.5mcg/kg/min:éCObutnotHRandBP -Martinezetal.,Pediatrics,1992
• Undesiredeffect:– Arrhythmia– Vasodilation Osborn, Evans,Kluckow,Neoreviews2004
Ruoss,McPherson andDiNardo,Neoreviews,2015
Epinephrine• Endogenouscatecholamine• Receptors:alpha,beta• Predictabledose-dependentresponse(notinpreterms)
– 0.01- 0.1mcg/kg/min:betareceptors(b1>b2)– >0.1mcg/kg/min:alphareceptors(alpha1)
• NICU:oftenusedforrefractoryhypotension• UndesiredCVeffects:
– oxygenconsumption ofmyocardium– automaticity(arrhythmias)– Down-regulatesreceptors
• Non-CVeffects:• HypoK:B2mediatedKinflux tomusclecells• Hyperglycemia: glycolisisandsupressesinsulin release• Intestinalhypoperfusion -Cheung etal.,1997• Extravazationinjury
Osborn, Evans,Kluckow,Neoreviews2004Ruoss,McPherson andDiNardo,Neoreviews,2015
Norepinephrine• Endogenouscatecholamine• Receptor:alpha1and2(ééSVR-potentvasoconstrictor).LessextentB1and2.
• Doses:0.01-0.4mcg/kg/min• Undesiredeffects:
– afterloadtotheheart(workload)– Poorend-organperfusion(kidneysandgut)- tissueischemia– Extravazationinjury
• Usualindications:lowSVR(vasodilated-septicshock),hypertrophiccardiomyopathieswithhypotension
Osborn, Evans,Kluckow,Neoreviews2004Ruoss,McPherson andDiNardo,Neoreviews,2015
Dopamineordobutamine?
-Dopamine: more effective in the short term treatment of hypotension in preterm infant-No evidence of adverse neurological sequelae (severe P/IVH and/or PVL)
Subhedar andShaw,Cochrane2003
“intheabsenceofdataconfirminglongtermbenefit…dopaminecomparedtodobutamine,nofirmrecommendationscanbemaderegardingthechoiceofdrugtotreathypotension.”
Milrinone• Bipyridinegroup:selectivephosphodiesterase-3inhibitor.• IncreasescytosoliccAMPw/oreceptormechanism:positive
inotropicandlowersSVR(Inodilator)asperpetuates influxofCalcium=éCO
• Pulmonaryhypertension:weakvasodilator• DrugofchoicetobalanceQP:QSandpreventLCOSaftercardiac
surgery• Doses:0.25-1mcg/kg/min• UndesiredCVeffects:
– Hypotension– Tachycardia/arrhythmia
• Non-CVeffects:– Thrombocytopenia– Carefuladministrationwhenrenaldysfunction
Osborn, Evans,Kluckow,Neoreviews2004Ruoss,McPherson andDiNardo,Neoreviews,2015
DopamineorEpinephrine?
– Dcauses10%decreaseLVoutput secondarytodropinLVstrokevolume;EincreasesLVoutput by10%duetoincreaseinLVS
– Conclusion:“Epinephrinehasbettereffectoncontractility”
•20pts, >1750g•D:5,10,15,20mcg/kg/min•E:0.125,0.250,0.375,0.5mcg/kg/min
•60pts,<1501g•D:2.5,5,7.5,10mcg/kg/min•E:0.125,0.250,0.375,0.5mcg/kg/min
– Nodifferencesfoundratetreatmentfailure– Conclusion:“Low/mod-dose Eisaseffectiveaslow/moddoseD fortreatment
hypotension inlowbirthweightinfants,althoughisassociatedwithmoretransitoryadverseeffects”
Pediatrics,2006
MORESTUDIESNEEDED!
Steroids
• Mechanismofaction:– Decreasesthebreakdownofcatecholamines– Increasescalciumlevelsinmyocardialcells– Upregulates adrenergicreceptors– Innapropriate cortisol secretionduringsickness(relativeadrenal
insufficiency)• Dose:50mg/m2/day• Adverseeffects:
– Hyperglycemia– Gastricirritation– Fluidretention– Long-term:osteopenia,immunossupression,decreasedsomatic
growth,asseptic acetabular necrosis
Ruoss,McPherson andDiNardo,Neoreviews,2015
Frank-StarlingCurveThehearthasanintrinsiccapabilitytoincreaseitsforceofcontractionandthereforestrokevolume(SV)inresponsetoan
increaseinvenous return. ThisiscalledtheFrank-Starlinglaw(Fig2).Theraiseofvenous returnincreasestheventricularfilling(end-diastolicvolume)andthereforepreload,whichextendsthemyocyte sarcomerelength,causinganincreasein
forcegeneration.Theunderlyingmechanismisfound in thelength-tension andforce-velocityrelationships forcardiacmyocytes.Briefly,increaseofsarcomerelengthenhancestroponin Ccalciumsensitivity, whichupregualtes therateofmyosin-actinattachmentanddetachment,andtheamountoftension developedbythemusclefiber.
Isthereadescendinglimbofthestarlingcurve?
HeartFailureContractility
Isoproterenol
• Syntheticcatecholaminestructurallyrelatedtoadrenaline
• Receptor:almostexclusivelyBeta(éHR)• Doses:0.01-0.1mcg/kg/min• Undesiredeffects:
– oxygenconsumptionofmyocardium– automaticity(arrhythmias)– Extravazationinjury
• Usualindications:congenitalheartblock,PPHN,posthearttransplant(denervatedheart)
Osborn, Evans,Kluckow,Neoreviews2004
Vasopressin• NeuropeptideactingonV1andV2receptorsonsmooth
musclecellsandNOselectivevasodilationofcerebralandpulmonarycirculations
• Possiblesynergisticactiontocathecolamines• Peripheralvasoconstr(exceptCNS,coronary,gut,lungs)• Uses:
– Septicshock– Post-CPB
• Doses:0.0001-0.002Units/kg/min• Adverseeffects:vasoconstriction,tissuenecrosisand
hyponatremia
Maffei,PediatricCriticalCareStudyGuide,2012Ruoss,McPherson andDiNardo,Neoreviews,2015
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