Congenital heart disease: shunts and bubble precautions
Stem
A 6-month-old boy, 6.5 kg, with unrepaired tetralogy of Fallot is scheduled for complete repair in six weeks. Last night an incarcerated inguinal hernia was reduced manually, and the surgeons want to repair it today. His baseline SpO2 is 86% on room air, he takes propranolol, and his last echo showed a large VSD with moderate infundibular stenosis. He has fasted 6 hours for formula and has an IV.
Question
What are your hemodynamic goals, and how will you induce him?
Ideal answer
HeadlineKeep blood flowing to his lungs: systemic resistance up, preload full, and nothing that tightens the infundibulum or raises pulmonary resistance.1
- Continue propranolol; maintenance fluid; warm room. So fasting does not dehydrate him.
- De-air every line; check the syringes. With a right-to-left shunt, air goes straight to brain or coronaries.2
- IV ketamine 2 mg/kg, then fentanyl and rocuronium. About 13 mg; fentanyl 1 to 2 mcg/kg, rocuronium 0.6 mg/kg, about 4 mg. Ketamine supports systemic resistance.2,1
- Phenylephrine 5 to 10 mcg/kg drawn up first, because raising SVR pushes blood back to the lungs; 30 to 65 mcg for him.3
- Oxygen, modest pressures, normocarbia, warmth, adequate depth plus caudal. So incision causes no catecholamine surge.
Watch for: saturation as pulmonary blood flow, end-tidal CO2 falling with pulmonary flow, and the murmur, which softens in a spell.
Breaking down the answer
- Say the shunt determinants — right-to-left flow across the VSD rises when SVR falls or RVOT obstruction worsens; that sentence is the scientific rationale the examiner is listening for.1
- Bubble precautions beyond lines — any right-to-left or bidirectional shunt can carry venous air to the systemic circulation; some practitioners also avoid nitrous oxide for the same reason.2,4
- Why not propofol — agents that drop SVR (propofol, high-dose volatile) increase the shunt.1 Changes if: a left-to-right lesion without heart failure, where an inhalational induction is well tolerated.4
- No beta-agonists for hypotension — dopamine and epinephrine worsen infundibular spasm; I use phenylephrine.1
- Contrast the left-to-right shunt — in a large VSD, high oxygen and hyperventilation drop PVR and steal systemic flow, so I limit FiO2 and aim for saturations in the low to mid 90s.4
- Endocarditis prophylaxis is for dental procedures — unrepaired cyanotic heart disease qualifies, but the 2021 AHA statement addresses dental procedures, not a hernia repair.5
Follow-up question
At skin incision his saturation falls from 86 to 58%, heart rate rises to 170, end-tidal CO2 drops and the murmur disappears.
What is happening and what do you do?
Follow-up answer
HeadlineA hypercyanotic tet spell: infundibular spasm from a catecholamine surge, pulmonary flow collapsing. I tell the surgeon to stop and announce it.
100% oxygen with low airway pressures, and a deeper anesthetic with fentanyl, watching for a drop in SVR.2 A fluid bolus for preload and phenylephrine 5 to 10 mcg/kg for systemic resistance, repeated or as an infusion.3 Knees to chest or abdominal compression.2 If it persists, esmolol 0.5 mg/kg relaxes the infundibulum.2 I reassess saturation, end-tidal CO2 and the returning murmur, send a gas, and call cardiology and the cardiac surgeons if he does not respond.
Pitfalls that cost points
- Forgetting bubble precautions or saying they matter only for left-to-right shunts.
- Choosing a mask induction when he already has an IV: deep volatile lowers SVR and increases the right-to-left shunt.1
Rapid-fire
Q: Name the four lesions. A: VSD, right ventricular outflow obstruction, overriding aorta and right ventricular hypertrophy.2
Q: When does a left-to-right shunt cause heart failure symptoms? A: When Qp:Qs reaches about 1.5 or more.4
Q: Which beta-blocker bolus in a spell? A: Esmolol 50 to 200 mcg/kg titrated, or propranolol 0.1 mg/kg slowly.3
Q: Prophylaxis dose before dental work? A: Amoxicillin 50 mg/kg orally, 30 to 60 minutes before.5
Q: How does a right-to-left shunt affect inhalational induction? A: It slows it, because part of the blood bypasses the lungs.
Numbers to know
| Item | Value |
|---|---|
| Ketamine IV induction | 2 mg/kg2 |
| Rocuronium | 0.6 mg/kg2 |
| Phenylephrine for a spell | 5–10 mcg/kg3 |
| Esmolol | 0.5 mg/kg (SPA); 50–200 mcg/kg titrated (OpenAnesthesia)2,3 |
| Qp:Qs with symptoms | ≥1.54 |
| IE prophylaxis | Amoxicillin 50 mg/kg, 30–60 min before dental work5 |
Links
- Adult congenital heart disease, Pulmonary hypertension and right ventricular failure, Venous air embolism and the sitting position, Choosing an induction agent, Vasopressors and inotropes: choosing and titrating
- SPA Case Guides: Tetralogy of Fallot; Ventricular Septal Defects; AHA Scientific Statement on Infective Endocarditis Prevention (2021)
Sources
- 1.Tetralogy of Fallot: anesthetic management · OpenAnesthesia · openanesthesia.org
- 2.Tetralogy of Fallot (SPA Case Guide) · Society for Pediatric Anesthesia, 2023 · www2.pedsanesthesia.org
- 3.Tet spell: pharmacologic treatment · OpenAnesthesia · openanesthesia.org
- 4.Ventricular Septal Defects (SPA Case Guide) · Society for Pediatric Anesthesia, 2025 · pedsanesthesia.org
- 5.Prevention of Viridans Group Streptococcal Infective Endocarditis: A Scientific Statement From the AHA (Circulation 2021) · AHA, 2021 · smilegeneration.comFull-text PDF copy of the AHA statement; Table 3 lists conditions, dental procedures only.
Facts on this page were checked against these sources on Oct 15, 2026. Guidelines change; confirm doses against current institutional protocols.