What emergency department interventions are indicated for a toddler or preschool‑aged child with tetralogy of Fallot presenting with an acute cyanotic spell?

Emergency Department Management of Acute Cyanotic Spells in Tetralogy of Fallot

For a toddler or preschool-aged child with tetralogy of Fallot presenting with an acute hypercyanotic spell, immediately place the child in knee-chest position, administer 100% oxygen, give morphine sulfate 0.1-0.2 mg/kg IV/IM/SC, and provide a normal saline bolus of 10-20 mL/kg. 1

Immediate First-Line Interventions (Perform Simultaneously)

Positioning and Oxygen

• Place the child in knee-chest position to increase systemic vascular resistance (SVR), decrease right-to-left shunting, and improve pulmonary blood flow 1
• Administer 100% oxygen via face mask or non-rebreather to maximize oxygen delivery, though saturation may not improve dramatically due to persistent right-to-left shunting 1, 2

Pharmacologic Management

• Give morphine sulfate 0.1-0.2 mg/kg IV/IM/SC as the primary sedative agent—this reduces infundibular spasm (the key pathophysiology), provides sedation, decreases respiratory drive, and reduces oxygen consumption 1, 2
• Administer IV fluid bolus of 10-20 mL/kg normal saline to increase preload, improve cardiac output, and enhance pulmonary blood flow 1

Essential Monitoring

• Establish continuous pulse oximetry and cardiac monitoring 1, 2
• Monitor blood pressure intermittently (umbilical artery catheter if neonate, or non-invasive cuff) 3
• Consider cerebral oxygen saturation monitoring if available 1, 2

Second-Line Interventions (If Spell Persists After 5-10 Minutes)

Vasopressor Therapy

• Administer phenylephrine 5-10 μg/kg IV bolus, followed by continuous infusion if needed 1, 2, 4
  • Phenylephrine increases SVR, forcing more blood through the pulmonary circulation and reducing right-to-left shunting 1, 4
  • This is particularly effective when infundibular spasm is the primary mechanism 4
• Alternative: Epinephrine 10 μg/kg IV can be used instead of phenylephrine for refractory spells 1

Emergency Rescue Interventions (For Refractory Spells)

Airway Management

• Prepare for intubation and controlled ventilation if the spell does not resolve with above measures 1
• Use ketamine 1-2 mg/kg IV for sedation during intubation—ketamine maintains SVR while providing analgesia and sedation, making it ideal for this population 1, 2
• Avoid agents that decrease SVR or increase PVR 2

Advanced Interventions for Persistent Crisis

• Emergent cardiac catheterization if shunt thrombosis is suspected (in patients with prior Blalock-Taussig shunt), allowing prompt thrombus removal 1
• Emergent sternotomy for thrombectomy ("milking" the shunt) if catheter-based removal is not feasible 1
• Extracorporeal membrane oxygenation (ECMO) may be instituted if all other measures fail to stabilize hemodynamics and oxygenation 1

Critical Pitfalls to Avoid

• Do not use agents that decrease SVR (e.g., nitroglycerin, nitroprusside, ACE inhibitors) as these worsen right-to-left shunting 2
• Avoid excessive agitation or crying—these worsen the spell by increasing oxygen consumption and infundibular spasm 1
• Do not delay morphine administration while attempting IV access—give IM or SC if IV access is difficult 1
• Recognize that oxygen alone will not resolve the spell—the primary problem is mechanical (infundibular spasm) and hemodynamic (inadequate SVR), not simply hypoxemia 1, 2

Definitive Management Planning

• Expedite cardiology consultation and surgical evaluation for definitive repair 1
• Primary complete intracardiac repair in infancy achieves >98% hospital survival and >90% 30-year survival 1
• Recurrent hypercyanotic spells are an indication for urgent surgical intervention rather than continued medical management 1, 5

Alternative Sedation Options (If Standard Agents Unavailable)

• Intranasal midazolam has been reported as effective for initial calming in the emergency department setting, particularly when IV access is difficult 6
• Dexmedetomidine 0.2 μg/kg/min continuous infusion (without loading dose) has shown effectiveness in managing hypercyanotic spells with minimal respiratory depression 7

The key principle is that hypercyanotic spells result from dynamic infundibular obstruction causing decreased pulmonary blood flow and increased right-to-left shunting 1, 5. All interventions aim to break this cycle by reducing infundibular spasm (morphine), increasing SVR (positioning, phenylephrine), and optimizing preload (fluids) 1, 2.