A patient undergoing tonsillectomy under halothane anaesthesia requires infiltration of the surgical field with adrenaline-containing solution for haemostasis. Compared with other volatile agents, why is this combination particularly hazardous?
- A Halothane inhibits plasma cholinesterase, prolonging adrenaline action
- B Halothane sensitises the myocardium to circulating catecholamines, predisposing to ventricular arrhythmias ✓
- C Halothane potentiates adrenaline-induced peripheral vasoconstriction causing tissue necrosis
- D Halothane blocks beta receptors, causing unopposed alpha-mediated hypertension
Correct answer: B. Halothane sensitises the myocardium to circulating catecholamines, predisposing to ventricular arrhythmias
Explanation
Halothane slows conduction through the His-Purkinje system and increases myocardial automaticity, making ventricular ectopy and arrhythmias likely when exogenous adrenaline is absorbed. It is the volatile agent with the greatest catecholamine sensitisation; isoflurane and sevoflurane allow considerably higher adrenaline doses. The arrhythmogenicity is a direct myocardial electrophysiologic effect, not cholinesterase inhibition or receptor blockade, so options A, C and D describe mechanisms that do not apply.
Reference: Morgan and Mikhail's Clinical Anesthesiology, 7th ed.
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