Comparison of bupivacaine plus buprenorphine with bupivacaine alone by caudal blockade for post-operative pain relief after hip and knee arthroplasty.

In a double-blind, parallel group trial, 15 patients who were given a caudal injection of 1.8 mg kg-1 of bupivacaine after induction of anaesthesia, were compared with 15 patients in whom 7.2 mg kg-1 of buprenorphine was added to the same dose of bupivacaine, prior to knee or hip replacement surgery. The duration of analgesia was much longer (mean 606 min vs. 126 min P < 0.001) in those receiving added buprenorphine; mean morphine consumption in the first 24 h was halved (14 mg vs. 28 mg) and patient satisfaction greatly increased. There were no significant differences in the incidence of complications although the group which had added buprenorphine had a lower incidence of vomiting.