Which of the following is a primary intervention to manage a tet spell in an infant with Tetralogy of Fallot?

Managing a hypercyanotic spell requires knowledge of congenital heart defects and hemodynamics. Applying principles of systemic vascular resistance is essential to understand how physical positioning reduces right-to-left shunting and improves pulmonary blood flow during an acute Tetralogy of Fallot crisis. Choice A rationale While fluids can maintain preload, they are not the primary emergent intervention for an acute tet spell. Increasing systemic vascular resistance is more critical to immediately force blood into the pulmonary artery, whereas IV access takes too long to establish. Choice B rationale Cardiopulmonary resuscitation is reserved for cardiac arrest and is not the first-line treatment for a cyanotic spell. The infant typically has a pulse but suffers from acute hypoxia due to infundibular spasm and decreased pulmonary perfusion during agitation. Choice C rationale Placing the infant in a knee-to-chest position increases systemic vascular resistance. This physiological change reduces the right-to-left shunt across the ventricular septal defect, forcing more deoxygenated blood into the lungs for oxygenation, effectively resolving the cyanotic episode. Choice D rationale Oxygen is supplemental but often ineffective if the underlying shunt is not addressed. Without increasing systemic resistance via positioning, oxygen cannot reach the pulmonary circulation efficiently due to the physical obstruction and pressure gradients inherent in Tetralogy of Fallot.