Intrathecal morphine compared with diamorphine for postoperative analgesia following unilateral knee arthroplasty

Objectives: To compare the efficacy and side effects of low dose intrathecal morphine and diamorphine for postoperative analgesia after total knee arthroplasty.Methods: Sixty-four patients were included in a prospective, randomised, double-blind study. Following a standardised general anaesthetic technique, patients received either 0.3 mg of intrathecal morphine or diamorphine with 2–2.5 ml of 0.5% heavy spinal bupivacaine. Supplementary analgesia was provided postoperatively by regular eight hourly diclofenac and patient controlled IV morphine (bolus 1 mg, lockout 5 min, no background infusion).Results: Patients in the morphine group had significantly lower median numerical rating score (NRS) for pain on movement at 4 h 0 versus 3.5] (P=0.0008) and 8 h 0 versus 4] (P=0.0083). In addition, median PCA morphine consumption was significantly reduced at 4 h 0 versus 1] (P=0.0005), 8 h 0.5 versus 6] (P=0.0063) and 12 h 3 versus 8.5] (P=0.0426) in the morphine group. There was no significant difference in the total morphine consumption or NRS for pain at 24 h between the two groups. There was no significant difference in the incidence of side effects between the two groups.Conclusion: In the doses used in this study, morphine produced more effective analgesia than diamorphine in the early postoperative period with comparable side effects Acute Pain 4 (1) (2001) 7].