ORAL CLONIDINE PREMEDICATION ATTENUATES THE HEMODYNAMIC-EFFECTS ASSOCIATED WITH KETAMINE ANESTHETIC INDUCTION IN HUMANS

Induction of anaesthesia is often associated with undesirable variatio ns in blood pressure and heart rate. Clonidine has been demonstrated t o attenuate many of these undesirable effects when used as a premedica nt. Other alpha2 adrenergic agonists have been used to ameliorate the cardiostimulatory effects of ketamine in animals but there are few dat a on the use of this combination in humans. The effect of oral clonidi ne premedication, 5 mug . kg-1 on the haemodynamic changes induced by iv ketamine was studied in 42 patient volunteers. Ninety minutes befor e surgery, patients randomly received clonidine (C), diazepam (D), or a placebo (P) in a double-blinded fashion. Anaesthesia was induced wit h a ketamine infusion of 1 mg . kg-1 . min-1 until loss of consciousne ss. Heart rate and phasic blood pressure were measured noninvasively p rior to induction, before and up to seven minutes after tracheal intub ation. There were no differences in demographics or baseline vital sig ns among the three groups. With ketamine administration, increases in heart rate and blood pressure were less in those patients given C preo peratively than in those who received either D or P The peak increase in mean blood pressure was 39% (C) versus 70% (D) and 55% (P) (P < 0.0 1). Heart rate increased by a maximum of 20% (C) versus 41% (D) and 46 % (P) (P < 0.01). We conclude that oral clonidine attenuates the hyper dynamic effects of anaesthetic induction with iv ketamine.