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 effects of intrathecal morphine and nalbuphine, the endpoints being onset and offset of action.

METHODS: Geriatric patients scheduled for elective total hip replacement under continuous spinal anaesthesia were randomized to two double-blinded groups in the recovery room as soon as they experienced a pain score higher than 3 cm on the visual analogue scale (VAS, 0-10 cm). Either 160 microg morphine or 400 microg nalbuphine in 4 ml normal saline were administered intrathecally. Pain scores on VAS, rescue analgesia (diclofenac and morphine, not allowed during the first 60 min), and the adverse effects (respiratory depression, postoperative nausea and vomiting, itching) were recorded for 24 h after surgery.

RESULTS: The study was stopped after inclusion of 2 x 12 patients due to slow onset of analgesia in the morphine patients. In the nalbuphine group, when 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 intervention for a pain score >3 cm (218+/-256 vs. 1076+/-440 min, P<0.05) were significantly shorter. The analgesic requirements during the first 24 h were significantly lower in the morphine group (P<0.001).

CONCLUSION: We conclude that after total hip replacement, administration of intrathecal nalbuphine resulted in a significantly faster onset of pain relief and shorter duration of analgesia than intrathecal morphine.