Epidural morphine prophylaxis of postoperative pain: report of a double-blind multicentre study

In a double-blind placebo-controlled trial, 154 subjects, having intraperitoneal surgery or Caesarean section, and 53 patients undergoing lower limb orthopaedic surgery, received epidural morphine, 5 mg in 10 ml 0.9 per cent NaCl, or placebo, 10 ml 0.9 per cent NaCl, intraoperatively to determine duration of action and efficacy in preventing postoperative pain. Epidural morphine gave significantly longer postoperative analgesia (greater than 11 h) than placebo (3-6 h) in both groups (p less than 0.05) and patients who received morphine required less postoperative analgesic. Obstetric subjects experienced longer pain relief (18.3 +/- 1.3 h) than patients undergoing non-obstetric intraperitoneal surgery (9.2 +/- 1.2 h) (p less than 0.001). Generally mild pruritus affected more than 40 per cent of those receiving morphine, but over 90 per cent of obstetric patients receiving morphine. Respiratory depression occurred in 2-7 per cent of subjects who received morphine; unpredictable in onset, it responded rapidly to naloxone. Epidural bupivacaine, if employed for the surgical procedure, appeared to prolong epidural morphine analgesia. We consider epidural morphine useful in preventing postoperative pain, but its use demands close observation of respiratory rate in a high density nursing area.