Tetralogy of Fallot Tet Spell — FRCA Final MCQ

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HardPaediatric AnaesthesiaTetralogy of Fallot Tet SpellFRCA Final

A 2-year-old child weighing 12 kg with unrepaired tetralogy of Fallot develops a hypercyanotic spell during induction of anaesthesia. Despite 100% oxygen, flexion of the hips and knees towards the chest, reduction of stimulation and an IV 0.9% sodium chloride bolus of 10 mL/kg, SpO2 remains 55% and arterial pressure is 48/25 mmHg. Which is the most appropriate next intravenous drug?

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Correct answer: D — Phenylephrine 5 micrograms/kg

The correct answer is D. This child has a persistent hypercyanotic spell with profound hypotension despite oxygen, positioning and volume expansion. Phenylephrine is a predominantly alpha-1 agonist: increasing systemic vascular resistance and aortic pressure reduces right-to-left flow across the VSD and promotes pulmonary blood flow. The calculated dose is 5 micrograms/kg × 12 kg = 60 micrograms IV. Propranolol 100 micrograms/kg can reduce tachycardia and dynamic infundibular obstruction, but is not the best first drug while systemic pressure is critically low and may worsen hypotension. Atropine increases heart rate, while adrenaline at 10 micrograms/kg produces marked beta-adrenergic stimulation and is a paediatric cardiac-arrest dose; both may aggravate dynamic RV outflow obstruction. Adenosine treats re-entrant supraventricular tachycardia, not a tet spell.

Reference: Sheffield Children's NHS Foundation Trust. Management of hypercyanotic spells in children with Tetralogy of Fallot, guideline 3.48. Implemented August 2023; review August 2026. https://www.sheffieldchildrens.nhs.uk/download/1720/medical-emergencies/64184/3-48-management-of-hypercyanotic-spells-in-children-with-tetralogy-of-fallots.pdf