A double-blind comparison of epidural ketamine and diamorphine for postoperative analgesia

Twenty patients who had abdominal hysterectomy under general anaesthesia were randomly assigned to receive either epidural ketamine (30 mg), or epidural diamorphine (5 mg) peri-operatively and on first request for analgesia. Failure to obtain satisfactory analgesia with one of the agents was treated by epidural administration of the other. Pain was assessed by an independent observer, and by the patient using a visual analogue scale. The mean (SD) pain score on recovery from general anaesthesia, on a scale of 0-4, was 2.9 (1.2) for the ketamine group and 1.0 (1.0) for the diamorphine group (p less than 0.01). The mean (SD) time to first request for analgesia was 272 (206) and 72 (41) minutes in the diamorphine and ketamine groups respectively (p less than 0.01). All patients in the diamorphine group obtained adequate analgesia, but all patients in the ketamine group were changed to epidural diamorphine. Epidural ketamine does not appear to be a sufficiently effective alternative to epidural diamorphine for routine use in postoperative pain.