Optimum dose of epidural morphine for postsurgical analgesia.

To determine the optimum dose of epidural morphine for postoperative pain control, 0.5-4.0 mg of morphine was administered to 198 patients who had undergone operations on lower abdomen or lower extremities under continuous epidural anesthesia. Analgesic effect of morphine and incidence of nausea or vomiting were studied using linear discriminant analysis. As explanatory variables, age and dose of morphine were statistically significant in discriminating analgesic effect of morphine. Among indices for physique of patients, height was the most useful for predicting the analgesic effect. The dose which made the discriminant function zero corresponded to the minimum effective dose (MED) of morphine and it was expressed as follows; MED (mg.meter(-1)) = -0.0107 x age + 1.85. Predicting the incidence of nausea or vomiting in relation to the dose of morphine did not reach a level of statistical significance.