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.