A 2-year-old child with known Tetralogy of Fallot suddenly develops paroxysmal hypercyanosis, irritability, and loss of consciousness during crying. Which of the following is the LEAST appropriate initial intervention for this hypercyanotic spell?

• A Knee-chest position to increase systemic vascular resistance
• B Morphine sulphate 0.1 mg/kg subcutaneous to reduce infundibular spasm and calm the infant
• C Intravenous phenylephrine to increase systemic vascular resistance and reduce right-to-left shunting
• D Intravenous isoproterenol to increase heart rate and improve pulmonary blood flow ✓

Explanation

During a 'tet spell', dynamic right ventricular outflow tract (RVOT) obstruction worsens, increasing right-to-left shunting. Management aims to increase SVR (knee-chest position, phenylephrine, propranolol to reduce HR and relax RVOT), sedate (morphine reduces hyperpnea and infundibular spasm), and correct acidosis. Isoproterenol is a beta-agonist that increases heart rate and myocardial contractility—this would worsen the infundibular spasm and worsen the right-to-left shunt, making it contraindicated. It is the LEAST appropriate intervention.

Reference: Ghai Essential Pediatrics, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.