Comparison of the Analgesic Effects of Intrathecal Clonidine and Intrathecal Morphine After Spinal Anaesthesia in Patients Undergoing Total Hip Replacement

We have studied the anaesthetic and analgesic properties of intrathecal clonidine and intrathecal morphine in patients undergoing total hip replacement under spinal anaesthesia. After routine spinal anaesthesia with 0.5% plain bupivacaine 2.75 ml, patients were allocated randomly to receive intrathecal clonidine, morphine or saline (control) as adjuvant to the bupivacaine. Postoperative analgesic effects were measured by consumption of morphine via patient-controlled analgesia and visual analogue pain scores. Both intrathecal clonidine and intrathecal morphine prolonged the time to first analgesia compared with saline (mean 278 (SD 93.2) min, 498 (282.4) min and 54 (61.9) min, respectively) (P < 0.001). Total morphine consumption on the first night after operation was significantly less in the intrathecal morphine group. There were no differences between the clonidine and the control group. Intrathecal clonidine prolonged the duration of spinal analgesia, but was markedly inferior to the intrathecal morphine in providing subsequent postoperative analgesia.