During tympanoplasty under halothane anaesthesia, the surgeon infiltrates lignocaine with epinephrine for haemostasis. Shortly afterwards the monitor shows frequent ventricular premature beats. Which property of halothane best explains this event?
- A It sensitises the myocardium to circulating catecholamines, permitting triggered arrhythmias ✓
- B It blocks cardiac sodium channels, prolonging the QT interval
- C It causes reflex tachycardia through carotid body stimulation
- D It releases histamine, producing coronary vasospasm
Correct answer: A. It sensitises the myocardium to circulating catecholamines, permitting triggered arrhythmias
Explanation
Halothane slows conduction through the SA node and AV node and sensitises the myocardium to exogenous catecholamines, allowing re-entry and triggered ventricular arrhythmias when epinephrine is infiltrated locally. Conventional teaching limits epinephrine infiltration under halothane to doses below about 1.5 microgram per kilogram. Isoflurane also carries some arrhythmogenic potential but far less than halothane, while sevoflurane and desflurane are considered safest for catecholamine-containing solutions.
Reference: Morgan and Mikhail's Clinical Anesthesiology, 6th ed.
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