A 3-day-old neonate with Tetralogy of Fallot presents with severe cyanosis and a hypercyanotic spell. The infant is tachypneic, hypoxic (SpO₂ 65%), and irritable. Which drug is the first-line pharmacological agent to terminate this acute hypercyanotic episode?

Explanation

## Management of Hypercyanotic Spells in TOF **Key Point:** Morphine sulphate is the first-line drug for acute hypercyanotic spells in cyanotic heart disease, particularly Tetralogy of Fallot. ### Mechanism of Action Morphine works through multiple pathways: 1. **Systemic vasodilation** — reduces right-to-left shunt by decreasing systemic vascular resistance 2. **Pulmonary vasodilation** — improves pulmonary blood flow 3. **Sedation and anxiolysis** — reduces catecholamine surge and metabolic demand 4. **Reduces myocardial contractility** — decreases the right ventricular outflow tract obstruction ### Dosing in Acute Spell - **IV morphine:** 0.1–0.2 mg/kg IV push (rapid onset in 5–10 minutes) - Can repeat every 15–30 minutes if needed - Onset faster than oral propranolol ### Comparison of Agents in Hypercyanotic Spells | Agent | Role | Onset | Use in Acute Spell | |-------|------|-------|--------------------| | **Morphine** | First-line acute | 5–10 min (IV) | **YES — immediate** | | **Propranolol** | Prophylaxis + acute | 30–60 min (oral) | Secondary (chronic prevention) | | **Prostaglandin E1** | Keep ductus arteriosus patent | Minutes | Neonates with duct-dependent lesions (not TOF) | | **Milrinone** | Inotrope + pulmonary vasodilator | Minutes | Cardiogenic shock, not first-line for spells | **High-Yield:** In a hypercyanotic spell, the **immediate goal** is to break the cycle of increasing right-to-left shunt. Morphine achieves this fastest. **Clinical Pearl:** The classic position adopted by infants during a spell — **squatting** — mimics the hemodynamic effect of morphine by increasing systemic vascular resistance and reducing right-to-left shunt. ### Adjunctive Measures - Knee-chest position (if older child) - Oxygen therapy (though limited benefit in TOF due to fixed right-to-left shunt) - IV fluids (increase preload) - Sedation (reduce catecholamine surge) **Warning:** Propranolol is used for **chronic prophylaxis** of spells (0.5–1 mg/kg/dose oral TDS), not for acute termination — it has a slower onset and is not suitable for an acutely cyanotic, hypoxic infant. [cite:Park 26e Ch 11]