Epidural morphine for postoperative pain relief: a dose-response curve

Different doses of epidural morphine were studied in order to determine their effectiveness in providing postoperative pain relief after surgery of the lower extremities and their relationship to the incidence of untoward reactions. The study was carried out in a double-blind fashion using five dosages of epidural morphine (0.5, 1.0, 2.0, 4.0, and 8.0 mg) and included 60 patients. The higher doses of morphine (2.0, 4.0, and 8.0 mg) were equally effective and more effective than the lower doses (0.5 and 1.0 mg) in providing postoperative analgesia. Nausea and vomiting were encountered more frequently with the highest dose (8.0 mg) and this finding was statistically significant (P less than 0.03). No statistically significant difference was found between the doses studied with regard to itching, urinary retention, and respiratory depression; the latter was evaluated in a subgroup of 20 patients. These data suggest that effective postoperative pain relief after surgery of the lower extremities can be achieved with relatively low doses of morphine sulfate and with minimal side effects. For the type of surgery studied, 2 mg morphine sulfate appeared to be the optimum dose.