Effect of clonidine on haemodynamic responses to endotracheal intubation and on gastric acidity.

Sixty-three patients (ASA 1-2), scheduled for elective surgery under general anaesthesia, were randomly given either oral clonidine (225-375 micrograms) + diazepam (5 15 mg), cimetidine (300 mg the night before and 300 mg in the morning) + diazepam or only diazepam for premedication. Anaesthesia was induced with thiopentone and maintained with N2O + O2 (70:30), enflurane and fentanyl. Vecuronium bromide was used as a muscle relaxant. The sleep dose of thiopentone was significantly smaller in the patients pretreated with clonidine than in the other groups. The mean maximal increase in heart rate was lowest in the clonidine-pretreated patients, but there were no significant differences in the mean arterial pressure changes associated with intubation. Before and just after intubation and in the recovery room, the arterial pressures were lowest in the patients pretreated with clonidine. During anaesthesia, marked bradycardia (less than or equal to 45 beats min-1) did not occur more often when clonidine was used, but in the recovery room there were statistically significantly more patients with bradycardia in the clonidine group than in the other groups. On the electrocardiogram (ECG) during the endotracheal intubation, the incidence of bigeminy was higher in the diazepam patients (5/20) than in the cimetidine patients (2/20) and the clonidine patients (0/23). There were significantly more gastric content samples with a pH above 2.5 in the cimetidine group than in the other groups, and clonidine patients did not differ from diazepam patients in this respect. The high incidence of bradycardia with the concomitant hypotension may limit use of this drug to highly selected patients.