Dose minimization study of single-dose epidural morphine in patients undergoing hip surgery under regional anesthesia with bupivacaine.

BACKGROUND: In order to decrease the rate of adverse effects, we aimed to identify the lowest analgesic dose of epidural morphine administered to patients undergoing hip surgery.

METHODS: Forty-five ASA I-II children undergoing surgical correction of hip dysplasia under caudal or epidural anesthesia with bupivacaine were randomized to receive epidural morphine 11.2, 15 or 20 microg.kg(-1) (groups 1, 2 and 3, respectively; 15 patients per group) immediately after completion of surgery. Postoperative pain control, sedation, motor block, urinary retention, pruritus and vomiting were evaluated.

RESULTS: In the recovery room, 46.7% of patients from group 1, 33.3% from group 2, and 93.3% from group 3 were sleeping but were easy to arouse (x(2) = 12.2; P < 0.005). The rest of the patients from each respective group were completely asleep. The cardiovascular and respiratory parameters were within normal limits. The ability to move the legs returned approximately 1 h after surgery in all three groups. Seven patients (46.7%) from group 1, nine (60%) from group 2, and 13 patients (86.7%) from group 3 vomited (x(2) = 5.4; P = 0.06). One patient receiving 20 microg.kg(-1) morphine experienced urinary retention. One patient receiving 15 microg.kg(-1) morphine suffered from pruritus. The duration of analgesia was similar, 12-14 h, in all three groups.

CONCLUSIONS: In patients undergoing hip surgery under regional anesthesia with bupivacaine, epidural morphine at a dose of 11.2 microg.kg(-1) administered immediately after completion of the procedure resulted in adequate pain relief for more than 12 h. Explanation of the high rate of patients vomiting (>45%) remains to be elucidated.