Onset and offset of intrathecal morphine versus nalbuphine for postoperative pain relief after total hip replacement

Background: We designed this study to compare the postoperative analgesic e ffects of intrathecal morphine and nalbuphine, the endpoints being onset an d offset of action. Methods: Geriatric patients scheduled for elective total hip replacement un der continuous spinal anaesthesia were randomized to two double-blinded gro ups in the recovery room as soon as they experienced a pain score higher th an 3 cm on the visual analogue scale (VAS, 0-10 cm). Either 160 mu g morphi ne or 400 mu g nalbuphine in 4 mi normal saline were administered intrathec ally. Pain scores on VAS, rescue analgesia (diclofenac and morphine, not al lowed during the first 60 min), and the adverse effects (respiratory depres sion, postoperative nausea and vomiting, itching) were recorded for 24 h af ter surgery. Results: The study was stopped after inclusion of 2 x 12 patients due to sl ow onset of analgesia in the morphine patients. In the nalbuphine group, wh en compared to the morphine group, the time to a pain score <3 cm (8+/-6 vs . 31+/-32 min, P<0.001), the time to the lowest pain score (18+/-11 vs. 66/-75 min, P<0.001) and the time to the first systemic analgesic interventio n for a pain score >3 cm (218+/-256 vs. 1076+/-440 min, P<0.05) were signif icantly shorter. The analgesic requirements during the first 24 h were sign ificantly lower in the morphine group (P<0.001). Conclusion: We conclude that after fetal hip replacement, administration of intrathecal nalbuphine resulted in a significantly faster onset of pain re lief and shorter duration of analgesia than intrathecal morphine.