The efficacy of intravenous 0.15 versus 0.25 mg/kg intraoperative morphinefor immediate postoperative analgesia after remifentanil-based anesthesia for major surgery

We evaluated the effect of perioperative administration of two doses of mor phine for postoperative analgesia after remifentanil-based anesthesia. The prospective, randomized study included 245 patients from 33 centers. All pa tients were scheduled for abdominal or urological surgery lasting more than 1 h. General anesthesia used remifentanil as the perioperative opioid (1 m u g/kg as a bolus then, 0.5 mu g/kg as a continuous infusion). A morphine b olus of 0.15 mg/kg (0.15-mg group) or 0.25 mg/kg (0.25-mg group) was admini stered 30 min before the end of surgery. In the postanesthesia care unit, p ain scores for patients were evaluated by using behavioral pain scores of 1 -3, verbal pain scores of 0-3, and visual analog scale scores of 0-10). Pos toperative analgesia was obtained by a morphine titration (3 mg every 5 min ). Demographic and surgery characteristics were similar in both groups. The delay for first demand of morphine was similar in the 0.15-mg and the 0.25 -mg groups (26 [9-60] and 30 [10-60] min, respectively). The frequency of m orphine titration was similar in both groups (75% and 66%, respectively). T he amount of morphine used in the postanesthesia care unit was smaller in t he 0.25-mg group (0.16 [0.0-1.25] vs 0.10 [0.0-0.56] mg/kg; P = 0.008). In the 0.25-mg group, the behavioral pain score was lower at 15 min, the verba l pain score was lower at 60 min (P < 0.001), and similar at 30 min. The vi sual analog scale pain score at 30 min and 60 min was similar in both group s. The incidence of minor side effects was similar in both groups. However, three cases of postoperative respiratory depression occurred in the 0.25-m g group compared with no cases in the 0.15-mg group. In conclusion, periope rative administration of morphine alone does not provide entirely adequate immediate postoperative pain control after remifentanil-based anesthesia in major surgery. Implications: The administration of 0.15 or 0.25 mg/kg peri operative morphine during remifentanil-based anesthesia for major surgery d oes not preclude additional morphine administration in the postanesthesia c are unit. The larger dose of 0.25 mg/kg slightly improves postoperative ana lgesia; however, it may be responsible fur postoperative respiratory depres sion.