Extradural clonidine infusions for analgesia after total hip replacement.

We have examined the effectiveness of extradural clonidine infusions for postoperative analgesia and the effect of clonidine on extradural morphine. In a double-blind, controlled study, patients, undergoing total hip replacement were allocated randomly to receive one of two doses of extradural clonidine (25 micrograms h-1 or 50 micrograms h-1), low dose extradural morphine or a combination of morphine and clonidine. Pain scores in the morphine group were significantly greater than in the clonidine groups (P less than 0.01) and the combination group (P less than 0.05) during the first 1 h after surgery. The requirements for systemic analgesia were least in the combination and larger dose clonidine group, and the duration of effect of the initial bolus dose was significantly longer compared with the morphine and low dose clonidine groups (P less than 0.05). Arterial pressure was reduced in the clonidine groups, although the incidence of clinical hypotension was low. There were no significant differences between the groups in emetic symptoms or urinary retention.