Intrathecal morphine dose-response data for pain relief after cholecystectomy.

We studied the effect of low-dose intrathecal morphine (0.00-0.20 mg) on pain relief and the incidence of side effects after cholecystectomy in 139 patients divided into eight groups according to intrathecal morphine dose: groups 1 (0.00 mg), 2 (0.04 mg), 3 (0.06 mg), 4 (0.08 mg), 5 (0.10 mg), 6 (0.12 mg), 7 (0.15 mg), and 8 (0.20 mg). Preservative-free morphine hydrochloride mixed in hyperbaric tetracaine solution was administered at the time of induction of spinal anesthesia just before surgery. Pain relief was significantly greater for the first 24 h in groups 3, 4, 5, 6, 7, and 8 than in group 1. The incidence of respiratory depression was significantly greater in groups 7 and 8 than in the other groups in the first 48 h. Vomiting occurred significantly more often in group 1 than in groups 2, 3, 4, and 5. Intraoperative cholangiography and the postoperative clinical course indicated no increase in tone of the sphincter of Oddi in any patient. We conclude that 0.06-0.12-mg intrathecal morphine is the best dose range for pain relief after cholecystectomy without respiratory depression and with the lowest incidence of vomiting or pruritus, or both.