A 4-month-old infant with Tetralogy of Fallot presents with sudden-onset severe cyanosis, rapid breathing, and loss of consciousness during feeding. On examination, the child is in acute distress. The structure marked **A** (pulmonary stenosis/RVOT obstruction) is the primary determinant of cyanosis severity in this condition. Which of the following is the MOST appropriate immediate management to reverse this acute hypercyanotic episode?

Explanation

## Why knee-chest position and oxygen is right The acute hypercyanotic spell (tet spell) in Tetralogy of Fallot is precipitated by infundibular spasm in the RVOT obstruction (structure **A**), which acutely increases right-to-left shunting across the VSD and causes severe cyanosis. The knee-chest position (squatting in older children) increases systemic vascular resistance (SVR), which reduces the pressure gradient favoring right-to-left shunting and reverses the acute cyanosis. Oxygen supplementation further improves arterial oxygenation. This is the first-line acute management according to Nelson Textbook of Pediatrics and Park's Pediatric Cardiology. Morphine is also given to calm the child and reduce infundibular spasm, but positioning and oxygen are the immediate life-saving interventions. ## Why each distractor is wrong - **Intravenous sodium bicarbonate and intubation**: While intubation may be needed if the child deteriorates, sodium bicarbonate is not indicated for acute tet spells. The primary problem is hemodynamic (increased R→L shunt), not metabolic acidosis requiring bicarbonate. Intubation is a later intervention if conservative measures fail. - **Intravenous furosemide and CPAP**: Diuretics and positive pressure ventilation are contraindicated in acute tet spells because they decrease SVR and increase intrathoracic pressure, both of which worsen right-to-left shunting and deepen cyanosis. - **Intravenous prostaglandin E1 and cardiac catheterization**: PGE1 is used to keep the ductus arteriosus patent in ductal-dependent lesions (e.g., critical pulmonary stenosis or pulmonary atresia), not for acute tet spell management. Emergency catheterization is not indicated for acute spell management; it is reserved for diagnostic or interventional purposes in stable patients. **High-Yield:** In tet spells, the knee-chest position increases SVR → reduces R→L shunt → reverses cyanosis. Remember: **position first, then morphine and oxygen**. [cite: Nelson Textbook of Pediatrics 21e; Park's Pediatric Cardiology for Practitioners 26e; Harrison's Principles of Internal Medicine 21e Ch 264]