PARTIAL REVERSAL OF THE EFFECTS OF EXTRADURAL CLONIDINE BY ORAL YOHIMBINE IN POSTOPERATIVE-PATIENTS

Extradural clonidine produces analgesia, with sedation, hypotension an d bradycardia, in postoperative patients. This study assessed if oral yohimbine would reverse these side effects. We studied 30 ASA I-II pat ients undergoing orthopaedic surgery. After operation they were alloca ted randomly to three groups to receive placebo, extradural clonidine 450 mug or extradural clonidine 450 mug plus oral yohimbine 16 mg. Pai n score was measured on a visual analogue scale (VAS); sedation was as sessed on a simple scale graded from 0 (awake and alert) to 3 (deeply sedated, awakening after tactile stimulations) and heart rate and arte rial pressure were monitored for 5 h. Yohimbine reversed the sedation induced by extradural clonidine, but also shortened the duration of an algesia (31 (sD 15) min, 186 (72) min and 126 (52) min in the placebo, extradural clonidine and extradural clonidine + yohimbine groups, res pectively) (P < 0.05), and did not reduce the hypotension and bradycar dia related to clonidine administration. These results suggest that al pha2 adrenoceptors are mediators of the sedation induced by clonidine and that the haemodynamic effects are not related to stimulation of su praspinal alpha2 receptors.