Respiratory depression following postoperative analgesia with epidural morphine

Eighteen healthy patients subjected to operation for duodenal ulcer were allocated randomly to one of two regimes of analgesic treatment with epidural morphine. The analgesic regime was started either per- or postoperatively. Epidural morphine in doses of 4 mg was given until satisfactory pain relief was achieved. PaCO2 and respiratory rate were measured hourly for 10 h and a nearly identical respiratory depression was found in the two groups. Peak PaCO2-values were seen in the 5th and 6th postoperative hour. The respiratory rate was initially high and declined during the first postoperative hours. Only one patient in each group had a pathologically low respiratory rate (8 min-1), but this was transient and seen in the 10th postoperative hour. The needs for epidural morphine on the first postoperative day were highest in the peroperative group. It is concluded that a peroperative start of pain treatment with epidural morphine does not affect the degree of respiratory depression or reduce the postoperative analgesic requirements.