Modification by halogenated anaesthetics of chronotropic response during reversal of neuromuscular blockade.

The effect of halothane and enflurane on changes in heart rate during reversal of neuromuscular block was compared in 48 adult patients. Premedication and anaesthetic technique were standardized. Either halothane or enflurane was the primary anaesthetic while pancuronium was used in all patients to achieve muscle relaxation. Ventilation was mechanically controlled and PaCO2 was between 30-40 mmHg. The neuromuscular block was reversed by an intravenous injection of atropine 1.2 mg and neostigmine 2.5 mg, given either separately or simultaneously, in different patient subgroups. Heart rate changes were significantly different between the halothane and enflurane groups. In general, reversal of neuromuscular block was accompanied by less fluctuations in heart rate after enflurane as compared to halothane anaesthesia. Simultaneous injection of atropine and neostigmine modified the tachycardiac response in the halothane sub-group only. Our observations suggest that use of enflurane offers an advantage over halothane in those patients in whom rapid fluctuations in heart rate during reversal of neuromuscular block may be dangerous.