Postoperative spinal analgesia with morphine.

Patients with pain after operation received morphine hydrochloride intrathecally in doses of 0.02 mg kg-1 (n = 30) and 0.2 mg kg-1 (n = 30). The high-dose group showed slightly longer-lasting and more potent analgesia than the low-dose group. Sedation, decreases in heart rate and systolic arterial pressure, oliguria, nausea and urinary retention were more frequent in the high-dose group. Two patients of the high-dose group showed evidence of respiratory depression which appeared after a late change in posture (7 and 11 h). We conclude that postoperative analgesia with intrathecal morphine 0.02 mg kg-1 must be followed by a prolonged head-up posture and be performed in hospital units where the treatment of respiratory depression is competent.