Single-Ventricle Single-Ventricle PhysiologyPhysiologyDr. Chi-Hsiang HuangDr. Chi-Hsiang Huang

Department of AnesthesiologyDepartment of Anesthesiology

National Taiwan University HospitalNational Taiwan University Hospital

IntroductionIntroduction

Physiology of the newborn (pre- and postoPhysiology of the newborn (pre- and postoperative)perative)

Bidirectional cavopulmonary anstomosis Bidirectional cavopulmonary anstomosis (bidirectional Glenn or hemi-Fontan)(bidirectional Glenn or hemi-Fontan)

Cavopulmonary anastomosis (Fontan)Cavopulmonary anastomosis (Fontan)

The NewbornThe Newborn

AnatomyAnatomy

In CHD, anatomy dictates physiologyIn CHD, anatomy dictates physiology Virtually all newborns with single-ventricle Virtually all newborns with single-ventricle

physiology have mixing of pulmonary and physiology have mixing of pulmonary and systemic venous returnsystemic venous return

The most important anatomic issue: the The most important anatomic issue: the outflow to and from the systemic ventricle outflow to and from the systemic ventricle and lungsand lungs

Systemic Outflow ObstructionSystemic Outflow Obstruction

Hypoplastic left heart syndrome (HLHS)Hypoplastic left heart syndrome (HLHS) Tricuspid atresia with transposed great artTricuspid atresia with transposed great art

erieseries Double-inlet left ventricleDouble-inlet left ventricle Critical AS, severe CoA, or IAACritical AS, severe CoA, or IAA DORV (some variations)DORV (some variations)

Systemic Outflow ObstructionSystemic Outflow Obstruction

Complete mixing of systemic and pulmonary venComplete mixing of systemic and pulmonary venous returnous return

Ventricular outflow directed primarily to the PAVentricular outflow directed primarily to the PA Systemic blood flow (QSystemic blood flow (Qss))

Largely by right-to-left ductal shuntingLargely by right-to-left ductal shunting Dependent on the relative PVR and SVRDependent on the relative PVR and SVR

Systemic outflow obstruction is poorly toleratedSystemic outflow obstruction is poorly tolerated Usually accompanied by signs or symptoms of sUsually accompanied by signs or symptoms of s

hock hock

HLHSHLHS

Pulmonary Outflow Pulmonary Outflow ObstructionObstruction

Tricuspid atresiaTricuspid atresia Pulmonary atresia with IVSPulmonary atresia with IVS TOF with pulmonary atresiaTOF with pulmonary atresia Severe Ebstein’s anomaly of the tricuspid Severe Ebstein’s anomaly of the tricuspid

valvevalve Critical PSCritical PS DORV (some variations)DORV (some variations)

Pulmonary Outflow Pulmonary Outflow ObstructionObstruction

Complete mixing of systemic and pulmonary venComplete mixing of systemic and pulmonary venous returnous return

Ventricular outflow predominantly directed out thVentricular outflow predominantly directed out the aortae aorta

Low pulmonary blood flow (QLow pulmonary blood flow (Qpp) in single-ventricle ) in single-ventricle

patients implies an obligate right-to-left shunt (gepatients implies an obligate right-to-left shunt (generally atrial level)nerally atrial level)

Clinical consequences of low QClinical consequences of low Qpp are variable are variable

Postoperative AnatomyPostoperative Anatomy

Goal of initial palliative surgery to establishGoal of initial palliative surgery to establish Unobstructed pulmonary and systemic veUnobstructed pulmonary and systemic ve

nous returnnous return Unobstructed systemic outflowUnobstructed systemic outflow Limited QLimited Qpp and PA pressure and PA pressure

Primary surgical optionsPrimary surgical options

Norwood OperationNorwood Operation CPB, cardioplegia, DHCA, ischemia-reperfusionCPB, cardioplegia, DHCA, ischemia-reperfusion

Blalock-Taussig Shunt Blalock-Taussig Shunt Low diastolic arterial pressure which may comprLow diastolic arterial pressure which may compr

omise coronary perfusionomise coronary perfusion Unilateral PA obstructionUnilateral PA obstruction

Pulmonary artery bandPulmonary artery band May increase the risk of subaortic obstruction anMay increase the risk of subaortic obstruction an

d ventricular hypertrophyd ventricular hypertrophy Unilateral PA obstructionUnilateral PA obstruction

Norwood OperationNorwood Operation

PhysiologyPhysiology

Ratio of pulmonary blood flow to systemic Ratio of pulmonary blood flow to systemic blood flowblood flow Total blood flow partitioned into Qp and QTotal blood flow partitioned into Qp and Q

ss Bases on the amount of anatomic obstructBases on the amount of anatomic obstruct

ion or vascular resistanceion or vascular resistance

Fick PrincipleFick Principle

QQss = VO = VO22 / (CaO / (CaO22 - CmvO - CmvO22))

QQpp = VO = VO22 / (CpvO / (CpvO22 – CpaO – CpaO22))

QQpp/ Q/ Qss = (SaO = (SaO22 – SmvO – SmvO22) / (SpvO) / (SpvO22 – SaO – SaO22))

QQpp/ Q/ Qss = 25 / (95 - SaO = 25 / (95 - SaO22))

Estimation of QEstimation of Qpp/ Q/ Qs s based on SaObased on SaO22

SmvOSmvO22

SmvOSmvO22 low, (SaO low, (SaO22 – SmvO – SmvO22) > 25) > 25 Shock: ductal dependent QShock: ductal dependent Qss Myocardial dysfunction following surgeryMyocardial dysfunction following surgery

When the decrease in SmvOWhen the decrease in SmvO22 is offset by i is offset by increased Qncreased Qpp/Q/Qss, SaO, SaO22 will remain unchang will remain unchangeded

SmvOSmvO22 monitoring following Norwood proc monitoring following Norwood procedureedure

SpvOSpvO22

SpvOSpvO22 likely to be normal in the absence of clinic likely to be normal in the absence of clinical or CXR evidence of pulmonary parenchymal dal or CXR evidence of pulmonary parenchymal diseaseisease

Unexpected pulmonary venous desaturation occUnexpected pulmonary venous desaturation occurred commonly, particularly with FiOurred commonly, particularly with FiO22 < 0.3 < 0.3

Failure to account for decreased SpvOFailure to account for decreased SpvO22 results i results in a falsely low calculation of Qn a falsely low calculation of Qpp/Q/Qss

Maneuvers that decrease SpvOManeuvers that decrease SpvO22 rather than Q rather than Qpp//QQss result in lower SaO result in lower SaO22 and reduced DO and reduced DO22 becaus because there is no increase in Qe there is no increase in Qss

ImplicationsImplications

Maximum DOMaximum DO22 occurs between a Q occurs between a Qpp/Q/Qss of appro of approximately 0.5 and 1 and dependent on the total Cximately 0.5 and 1 and dependent on the total COO

Small changes in QSmall changes in Qpp/Q/Qss can be associated with l can be associated with large changes in DOarge changes in DO22

DODO22 can be improved to a far greater degree by i can be improved to a far greater degree by increasing total CO than by altering Qncreasing total CO than by altering Qpp/Q/Qss

Once SaOOnce SaO22 becomes critically low, further decre becomes critically low, further decreases can no longer compensated for by increaseases can no longer compensated for by increases in Qs in Qss

Cardiac OutputCardiac Output

Low CO (QLow CO (Qpp + Q + Qss)) Low QLow Qss and low SaO and low SaO22

Low SaOLow SaO22 with clinical signs of low CO (an with clinical signs of low CO (an

uria, poor capillary refill, high ventricular filluria, poor capillary refill, high ventricular filling pressure, or metabolic acidosis out of ing pressure, or metabolic acidosis out of proportion to the degree of cyanosis) suggproportion to the degree of cyanosis) suggests poor cardiac functionests poor cardiac function

Ventricular DysfunctionVentricular Dysfunction

Single ventricle is volume loadedSingle ventricle is volume loaded Low QLow Qss, particularly with low diastolic blood pres, particularly with low diastolic blood pres

sure (large PDA) or a high end-diastolic ventriculsure (large PDA) or a high end-diastolic ventricular pressure (volume-loaded heart or after CPB) ar pressure (volume-loaded heart or after CPB) can cause coronary perfusion pressure to becocan cause coronary perfusion pressure to become critically lowme critically low

Compromise systolic ventricular function and furtCompromise systolic ventricular function and further raise EDP and lower SAP her raise EDP and lower SAP profound hemo profound hemodynamic decompensationdynamic decompensation

Manipulation of Delivered Manipulation of Delivered OxygenOxygen

Goal pf management:Goal pf management: Ensure adequate DOEnsure adequate DO22, not to maximize Sa, not to maximize Sa

OO22

Optimization of DOOptimization of DO22:: Maintenance of cardiac inotropy while balMaintenance of cardiac inotropy while bal

ancing Qancing Qpp and Q and Qss and maintaining adequat and maintaining adequate BP and SaOe BP and SaO22

ManagementManagement

Manipulation of QManipulation of Qpp/Q/Qss by manipulation of PVR by manipulation of PVR Management of total CO and SVR may be more Management of total CO and SVR may be more

effectiveeffective Keeping Hb 13-15 mg/dL can have a positive inflKeeping Hb 13-15 mg/dL can have a positive infl

uence on DOuence on DO22

Increased Hb increases SmvOIncreased Hb increases SmvO22 and SaO and SaO22 and d and d

ecreases Qecreases Qpp/Q/Qss in single-ventricle physiology in single-ventricle physiology

Manipulation of PVR and SVRManipulation of PVR and SVR

Manipulation of PVR and SVRManipulation of PVR and SVR

Subatmospheric oxygen (FiOSubatmospheric oxygen (FiO22 0.17-0.19) or resp 0.17-0.19) or respiratory acidosis can effectively raise PVR, decreiratory acidosis can effectively raise PVR, decrease SVR, and thus decrease Qase SVR, and thus decrease Qpp/Q/Qss in infants wit in infants with unrestricted Qh unrestricted Qpp

Subatmospheric oxygen may be associated with Subatmospheric oxygen may be associated with PV desaturation (particularly postoperative)PV desaturation (particularly postoperative)

Inhaled COInhaled CO22 in HLHS: increased cerebral and sy in HLHS: increased cerebral and systemic DO2stemic DO2

? Infants with low PVR and anatomically restricte? Infants with low PVR and anatomically restricted pulmonary blood flowd pulmonary blood flow

PEEPPEEP

PEEP increases PVR by compressing the interalPEEP increases PVR by compressing the interalveolar pulmonary arterioles in normal lung complveolar pulmonary arterioles in normal lung complianceiance

The nadir of PVR occurs at FRC rather than at zThe nadir of PVR occurs at FRC rather than at zero PEEPero PEEP

Initial PEEP applies radial traction forces and aiInitial PEEP applies radial traction forces and aids vascular recruitmentds vascular recruitment

Increases PEEP may prevent PV desaturation bIncreases PEEP may prevent PV desaturation by optimizing lung gas exchange and therefore dey optimizing lung gas exchange and therefore decrease Qcrease Qpp/Q/Qss

Manipulation of SVRManipulation of SVR

Intravenous vasodilatorIntravenous vasodilator Relatively greater effect on the systemic vasculatRelatively greater effect on the systemic vasculat

ure in poor systemic perfusion and low PVRure in poor systemic perfusion and low PVR Nitroprusside, phenoxybenzamine, inamrinone, Nitroprusside, phenoxybenzamine, inamrinone,

milrinonemilrinone -stimulation of myocardium with vasodilation ca-stimulation of myocardium with vasodilation ca

n further increase total CO without associated van further increase total CO without associated vasoconstrictionsoconstriction

Particularly valuable after DHCAParticularly valuable after DHCA Inappropriate Inappropriate SVR SVR QQpp, , QQss (BP, SaO2 (BP, SaO2 ), ),

masking potential warning signs of low Qmasking potential warning signs of low Qss

Inotropic SupportInotropic Support

Inotropic support that increases QInotropic support that increases Qss may also incre may also incre

ase SaOase SaO22 simply by increasing SmvO simply by increasing SmvO22

Dobutamine (5 and 15 Dobutamine (5 and 15 g/kg/min): g/kg/min): Q Qpp/Q/Qss

Epinephrine (0.05 and 0.1 Epinephrine (0.05 and 0.1 g/kg/min): g/kg/min): Q Qpp/Q/Qss

Dopamine (5 and 15 Dopamine (5 and 15 g/kg/min): g/kg/min): Q Qpp/Q/Qss

Low-dose epinephrine (0.05 Low-dose epinephrine (0.05 g/kg/min): greatest g/kg/min): greatest in PVR/SVR ratio, largely because of in PVR/SVR ratio, largely because of SVR SVR

DODO22 is increased dramatically by increasing total is increased dramatically by increasing total

CO and is optimized by adjusting QCO and is optimized by adjusting Qpp/Q/Qss

Combination of Combination of inotropic inotropic supportsupport and and decreasing Sdecreasing SVRVR is potentially the opti is potentially the optimal strategy to maximize mal strategy to maximize

DODO22..

High PVRHigh PVR Not all pulmonary overcirculationNot all pulmonary overcirculation Very low QVery low Qpp (PaO (PaO22 < 30 mmHg) < 30 mmHg)

pulmonary dead space and impair minute ventilationpulmonary dead space and impair minute ventilation Respiratory acidosis further Respiratory acidosis further PVR PVR

Alveolar recruitment strategies of ventilation in atelectasiAlveolar recruitment strategies of ventilation in atelectasis or pulmonary diseases or pulmonary disease

Minimum airway pressure, high-frequency jet ventilationMinimum airway pressure, high-frequency jet ventilation Supplemental inspired oxygen, hyperventilation, and alkaSupplemental inspired oxygen, hyperventilation, and alka

losislosis Inhaled NO, iv PGE1Inhaled NO, iv PGE1 BP by vasoconstriction may BP by vasoconstriction may Q Qpp and usually and usually SaO SaO22 b b

ut at the expense of some systemic perfusionut at the expense of some systemic perfusion

Bidirectional CavopBidirectional Cavopulmonary Anastomoulmonary Anastomo

sissis

AnatomyAnatomy

Second stage of single-ventricle palliationSecond stage of single-ventricle palliation SVC connected directly to the PA and otheSVC connected directly to the PA and othe

r sources of Qr sources of Qpp are either eliminated or sev are either eliminated or sev

erely restrictederely restricted Bidirectional Glenn and hemi-Fontan anstoBidirectional Glenn and hemi-Fontan ansto

mosesmoses

Hemi-FontanHemi-Fontan

Bidirectional GlennBidirectional Glenn

PhysiologyPhysiology

The driving force for QThe driving force for Qpp is SVC pressure is SVC pressure

QQpp must pass through two separate and hi must pass through two separate and hi

ghly regulated vascular beds: cerebral and ghly regulated vascular beds: cerebral and pulmonary vasculaturepulmonary vasculature

Removes the left-to-right shunt and thus thRemoves the left-to-right shunt and thus the volume load from the single ventriclee volume load from the single ventricle

SVC PressureSVC Pressure

Acute rise in SVC pressureAcute rise in SVC pressure Selection of patients with low PVR minimizSelection of patients with low PVR minimiz

es the risk from elevated SVC pressurees the risk from elevated SVC pressure Failure to maintain low SVC pressure lead Failure to maintain low SVC pressure lead

to problems maintaining adequate SaOto problems maintaining adequate SaO22

Small veno-venous collateral vessel contriSmall veno-venous collateral vessel contribute to arterial desaturationbute to arterial desaturation

Minimize SVC PressureMinimize SVC Pressure Minimize use of positive pressure, including PEEP, folloMinimize use of positive pressure, including PEEP, follo

wing surgerywing surgery Allow the end-expiratory lung volume to approximate FRAllow the end-expiratory lung volume to approximate FR

CC Minimal mean airway pressure and early extubation in paMinimal mean airway pressure and early extubation in pa

tient with healthy lungstient with healthy lungs Negative-pressure ventilation associated with increased QNegative-pressure ventilation associated with increased Qpp

Higher airway pressure to maintain FRC in pneumonia or Higher airway pressure to maintain FRC in pneumonia or ARDSARDS

Aprotinin and modified ultrafiltration: Aprotinin and modified ultrafiltration: transpulmonary pr transpulmonary pressure gradient, less pleural drainage, improved SaOessure gradient, less pleural drainage, improved SaO22

Vascular ResistanceVascular Resistance

QQpp largely dependent on resistance of 2 highly but diffe largely dependent on resistance of 2 highly but differentially regulated vascular bedsrentially regulated vascular beds

Cerebral and pulmonary vasculaturesCerebral and pulmonary vasculatures Opposite responses to changes in COOpposite responses to changes in CO22, acid-base status, , acid-base status,

and Oand O22 QQpp dependent on venous return through SVC (largely ce dependent on venous return through SVC (largely ce

rebral blood flow)rebral blood flow) Hyperventilation following bidirectional cavopulmonaHyperventilation following bidirectional cavopulmona

ry anastomosis impair cerebral blood flow and decreasry anastomosis impair cerebral blood flow and decrease SaOe SaO22

Inhaled NO may be the best treatment for high PVR anInhaled NO may be the best treatment for high PVR and low SaOd low SaO22 after bidirectional cavopulmonary anastom after bidirectional cavopulmonary anastomosis osis

Volume UnloadingVolume Unloading

The right-to-left shunt is eliminated and all QThe right-to-left shunt is eliminated and all Qpp is is

effective pulmonary floweffective pulmonary flow An acute increase in wall thickness and decreasAn acute increase in wall thickness and decreas

e in cavity dimension has been associated with ie in cavity dimension has been associated with improved tricuspid valve functionmproved tricuspid valve function

Preload and afterload are both decreasedPreload and afterload are both decreased Change in ventricular geometry may increase risChange in ventricular geometry may increase ris

k for systemic outflow obstruction in somek for systemic outflow obstruction in some

Total CavopulmonarTotal Cavopulmonary Anastomisisy Anastomisis

AnatomyAnatomy

Most common current approach to the FonMost common current approach to the Fontan operation tan operation Intracardiac lateral tunnelIntracardiac lateral tunnel

Less thrombogenic, possibility for growthLess thrombogenic, possibility for growth Extracardiac conduitExtracardiac conduit

Without cardioplegia, less arrhythmogenicWithout cardioplegia, less arrhythmogenic May be fenestratedMay be fenestrated

Fontan OperationFontan Operation

Fontan OperationFontan Operation

PhysiologyPhysiology

Hybrid of bidirectional cavopulmonary anastomoHybrid of bidirectional cavopulmonary anastomosis and normal cardiovascular physiologysis and normal cardiovascular physiology

QQpp dependent on systemic venous pressure, and dependent on systemic venous pressure, and

all Qall Qpp is effective is effective Elevated PAP (> 10-15 mmHg) is associated witElevated PAP (> 10-15 mmHg) is associated wit

h poor outcome, largely because it is difficult to h poor outcome, largely because it is difficult to maintain CVP in this range without large third-spmaintain CVP in this range without large third-space losses of fluidace losses of fluid

Fontan FenestrationFontan Fenestration

Providing a source of QProviding a source of Qss that is not that is not

dependent on passing through the dependent on passing through the pulmonary circulationpulmonary circulation

Decrease PAP enough to reduce third-Decrease PAP enough to reduce third-space losses of fluidspace losses of fluid

Low CO stateLow CO state

Essential to determine and treat the underlEssential to determine and treat the underlying causeying cause

Obstruction to QObstruction to Qpp

Low LAP, high CVP (or large third-space flLow LAP, high CVP (or large third-space fluid losses)uid losses)

Significant cyanosis in Fenestrated FontanSignificant cyanosis in Fenestrated Fontan If high PVR: OIf high PVR: O22, hyperventilation, alkalosi, hyperventilation, alkalosi

s, inhaled NOs, inhaled NO

Low CO stateLow CO state

Myocardial dysfunctionMyocardial dysfunction High LAP, high CVPHigh LAP, high CVP Ischemia-reperfusion injuryIschemia-reperfusion injury Poor preoperative myocardial functionPoor preoperative myocardial function Inotropic agents not increase ventricular afteInotropic agents not increase ventricular afte

rloadrload Phosphodiesterase inhibitorsPhosphodiesterase inhibitors DobutamineDobutamine Low-dose epinephrine (Low-dose epinephrine ( 0.05 0.05 g/kg/min)g/kg/min)

Mechanical circulatory supportMechanical circulatory support

THE ENDTHE END