Low-dose intrathecal diamorphine analgesia following major orthopaedic surgery

In a randomized double-blind study we examined the effect of adding diamorphine 0.25 mg and 0.5 mg to intrathecal bupivacaine anaesthesia for major orthopaedic surgery. Duration of postoperative analgesia was considerably greater in patients given either doses of intrathecal diamorphine than in a control group of patients given bupivacaine alone (P less than 0.001). However, there was no significant difference between the two diamorphine doses (0.25 mg and 0.5 mg), each providing prolonged analgesia (10.8 and 9.9 h, respectively). Although there was no evidence of late respiratory depression, the frequency of adverse effects, in particular urinary retention, nausea and vomiting, was high in both groups receiving intrathecal diamorphine.