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Pediatric Cardiac — Single Ventricle, Fontan Physiology, TOF Spell Management

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Pediatric Cardiac · 7 min read

The two pediatric cardiac scenarios most likely to appear on boards + most likely to walk into your OR for non-cardiac surgery: the Fontan adult and the TOF infant with a hypercyanotic spell.

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Single-ventricle palliation timeline

KeyHypoplastic left heart syndrome + tricuspid atresia + other single-ventricle anatomies follow a three-stage palliation.

Stage 1 (Norwood, neonate): reconstruct aortic arch + create systemic-to-pulmonary shunt (BT shunt or Sano RV-to-PA conduit).

Stage 2 (bidirectional Glenn, ~4-6 mo): SVC anastomosed to PA — upper-body venous return goes passively to lungs.

Stage 3 (Fontan, 2-4 yr): IVC also routed to PA (lateral tunnel or extracardiac conduit) — entire systemic venous return passively perfuses lungs without a sub-pulmonary pump.

The single ventricle pumps systemic only.

Single ventricle physiology: parallel circulation with one functional ventricle (HLHS, tricuspid atresia, double-inlet LV); balance Qp:Qs by adjusting SVR and PVR; survival depends on staged palliation (Norwood/Glenn/Fontan).

Fontan physiology — the four commandments

Preload-dependent: systemic venous pressure is the only driver of pulmonary flow.

Maintain euvolemia, avoid hypovolemia + avoid vasodilation.

Low PVR is essential: avoid hypercarbia, acidosis, hypoxia, hypothermia, sympathetic stimulation, high airway pressures.

Sinus rhythm matters: atrial kick is a significant fraction of cardiac output; treat arrhythmias aggressively, often cardiovert.

Spontaneous ventilation when possible — negative intrathoracic pressure augments pulmonary flow.

If mechanical ventilation required: low TV (6 mL/kg), high RR, low PEEP (≤5), short inspiratory time.

Resting SpO₂ 90-94% is normal for unfenestrated Fontan; fenestrated runs 85-90%.

Mitral stenosis (MS): obstruction to LV filling, fixed CO; maintain sinus rhythm, slow-normal HR (60-80) for diastolic filling, adequate preload, avoid PVR increase; LA dilation predisposes to AF.

Fontan anesthesia — practical pearls

KeyInduction: ketamine + etomidate preserve SVR + preload better than propofol bolus; if propofol used, titrate slowly.

Regional/neuraxial useful but watch sympathectomy — single-shot spinal causing 30% SVR drop is poorly tolerated; epidural with slow titration safer.

Avoid laparoscopic insufflation pressures >12 mmHg if possible (increased intrathoracic pressure + impaired venous return).

Always confirm sinus rhythm; have external pacing pads + cardioversion immediately available.

Late Fontan failure

protein-losing enteropathy
plastic bronchitis
hepatic fibrosis (Fontan-associated liver disease — surveillance ultrasound + LFTs)

Eisenmenger physiology: chronic L-to-R shunt causes pulmonary vascular remodeling and PVR rise, leading to shunt reversal (R-to-L), cyanosis; avoid decreased SVR, increased PVR; maintain preload.

Tetralogy of Fallot — the four lesions

VSD, (2) overriding aorta, (3) RV outflow tract obstruction (dynamic infundibular + fixed pulmonary valve stenosis), (4) RVH.

The degree of RVOT obstruction determines shunt direction.

Mild obstruction: left-to-right (pink TOF).

Severe obstruction: right-to-left through VSD cyanosis.

Definitive repair (VSD patch + RVOT relief) typically 3-6 mo; modern survival >95%.

Adult survivors present for non-cardiac surgery — chronic pulmonic insufficiency post-repair, RV dilation, risk of sudden death from VT.

Tetralogy of Fallot anatomy: RVOT obstruction (pulmonic stenosis), VSD, overriding aorta, RV hypertrophy; right-to-left shunt causes cyanosis; tet spells relieved by knee-chest position.

TOF spell (Tet spell) management

Hypercyanotic episode triggered by crying, fever, dehydration, inductioncatecholamine surgeinfundibular spasmmore RVOT obstructionmore right-to-left shuntingworsening cyanosiscycle.

Treatment cascade: (1) 100% O₂ + calm child + knee-chest position (increases SVR + decreases venous return).

Phenylephrine 5-10 mcg/kg IV bolus — raises SVR, redirects flow across pulmonary valve.

Fluid bolus 10-20 mL/kg — increases preload + stretches infundibulum open.

Propranolol 0.05-0.15 mg/kg IV slow — relaxes infundibular spasm.

Deepen anesthesia (ketamine 1-2 mg/kg useful — raises SVR).

Bicarbonate if acidotic.

Paradox: 100% O₂ alone doesn't help much — the cyanosis is from shunting, not lung disease.

Other key peds-cardiac syndromes — boards-relevant

KeyTGA (transposition): parallel circulations, ductal-dependent until atrial septostomy + arterial switch (~1 wk).

TAPVR (total anomalous pulmonary venous return): obstructed type is a neonatal emergency — pulmonary edema, severe pulmonary hypertension, mortality without urgent surgery.

Coarctation: ductal-dependent infants present with shock when PDA closes — prostaglandin E1 0.05-0.1 mcg/kg/min to reopen ductus.

Truncus arteriosus: single great vessel with VSD, balanced circulation depends on PVR — high FiO₂ drops PVR + steals from systemic.

Ebstein anomaly

apically displaced tricuspid valve
often with WPW — RA enlarged
RV small

Transposition of the great arteries (TGA): aorta from RV, PA from LV creates parallel circuits; survival depends on mixing via ASD/VSD/PDA; prostaglandin E1 maintains ductus until arterial switch.

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