Urinary retention during i.m. and extradural morphine analgesia

In the postoperative period fifty-six healthy patients undergoing cholecystectomy or operations for duodenal ulcer, received, in a randomized order, i.m., "high-level" or "low-level" extradural morphine. Thirty-five per cent in the i.m. group, 33% in the high-level group and 50% in the low-level group suffered urinary retention, in all cases within the first 24 h. The mean cumulative dose of morphine necessary for pain relief was in the same range (13.4-16.5 mg) during the first 2 h of therapy for all groups, while the amounts after 24 and 48 h were twice to four times with the i.m. route compared with the extradural route. A peripheral effect of morphine on the urinary bladder is possible and the mechanism of action is discussed.