A hypercyanotic 'tet spell' is occurring in a 6-month-old child with Tetralogy of Fallot. The child is squatting-equivalent (placed prone by the nurse) and is given 100% oxygen by mask. SpO2 remains 65% despite these measures. The most appropriate pharmacological intervention is:

• A IV propranolol to relax the RVOTO
• B IV phenylephrine to increase SVR and reduce right-to-left shunting ✓
• C IV morphine to reduce respiratory drive and RVOTO spasm
• D IV ketamine to sedate and increase pulmonary blood flow

Explanation

In a refractory hypercyanotic spell, IV phenylephrine (or IV propranolol for RVOTO relaxation and catecholamine blockade) is used. Phenylephrine increases systemic vascular resistance (SVR), which reduces right-to-left shunting across the VSD by raising systemic pressure above pulmonary. IV morphine blunts sympathetic drive and relieves RVOTO spasm and is an important early step, but if this fails, phenylephrine is the pharmacological agent of choice to correct the hemodynamic imbalance. Ketamine is generally avoided in untreated tet spells because tachycardia may worsen RVOTO.

Reference: Ghai Essential Pediatrics, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.