Comparison of the relative analgesic efficacies of epidural or intramuscular diamorphine following total knee arthroplasty

Abstract

Debate has proliferated as to the true site of action of opioids when placed in the epidural space. The aim of this study was to compare the analgesic effects of a bolus of diamorphine given by the epidural or intramuscular route. Sixty patients having elective primary total knee replacements were recruited and randomized to receive epidural or intramuscular diamorphine. A lumbar epidural catheter was sited and 10 mL of bupivacaine 0.5% wt vol-1 was injected. Patients subsequently received diamorphine 5 mg into the epidural space or as an intramuscular injection. Patient-controlled analgesia with intravenous morphine was used for postoperative analgesia. The primary outcome measures included time to first patient-controlled analgesia use and total morphine consumption in 24 h. Secondary end-points considered possible treatment complications. All primary end-points showed significant differences in favour of epidural diamorphine. Medians for times to first patient-controlled analgesia use and total 24 h morphine requirements were significantly different (P < 0.001) at 418 vs. 198 min and 11 vs. 39 mg, respectively. There were no significant differences in secondary end-points. This study has shown the superior analgesic efficacy of epidural diamorphine when compared to intramuscular injection.