Intraoperative clonidine enhances postoperative morphine patient-controlled analgesia

In this prospective study, the postoperative analgesic effects of intraoperative iv clonidine were evaluated. Two hundred consecutive patients undergoing major abdominal surgery were randomly assigned to either balanced anaesthesia with iv clonidine (Group 1) or balanced anaesthesia alone (Group 2). A PCA infuser was connected immediately after tracheal extubation. It was programmed to deliver morphine "on demand" iv boluses at doses of 1 mg for patients greater than 65 yr and 1.5 mg for women or 2 mg for men less than 65 yr old. A blinded observer assessed postoperative analgesia by recording the analgesic demands (both met and unmet), patient pain scores, sedation scores, and any side effects during the first 36 hr after surgery. Intraoperative clonidine reduced the number of analgesic demands during the observation period (45 +/- 27 demands in Group 1 vs 81 +/- 60 in Group 2, P = 0.0001). This resulted in a reduction in morphine delivered (55.4 +/- 30.6 mg vs 67.1 +/- 45.1 mg, P less than 0.05), mainly during the first 12 hr (19.7 +/- 11.1 mg vs 27.6 +/- 18.1, mg P less than 0.001) and the unmet demand rate was also reduced at all time intervals (P less than 0.01). Clonidine did not exacerbate sedation or side effects. However, clonidine provided better analgesia in men and in patients less than 65 yr of age. Intraoperative iv clonidine enhances morphine analgesia after abdominal surgery.