Dose-Response of Intrathecal Morphine When Administered With Intravenous Ketorolac for Post-Cesarean Analgesia: A Two-Center, Prospective, Randomized, Blinded Trial

Abstract Background The appropriate dose of intrathecal morphine for post-cesarean analgesia is unclear. With the inclusion of routine non-steroidal anti-inflammatory drugs, the required dose of morphine may be significantly less than the 200–300μg common a decade ago. We performed a two-center, prospective, randomized, blinded trial comparing three doses of intrathecal morphine, combined with routine intravenous ketorolac, in 144 healthy women undergoing elective cesarean delivery. Methods Patients received an intrathecal injection of hyperbaric bupivacaine 12mg, fentanyl 15μg and a randomized dose of 50, 100, or 150μg morphine in a volume of 2.2mL. Patients received intravenous ketorolac 30mg before leaving the operating room and 15mg intravenously every 6h for the duration of the study (24h). All received postoperative patient-controlled intravenous morphine. The primary endpoint was total intravenous morphine administered postoperatively over 24h, analyzed using mixed model regression. Results There were no differences between dose groups (or institutions) in intravenous morphine use over 24h. Visual analog scale scores for pain and nausea did not differ. Pruritus was greater in the 100 and 150μg groups than the 50μg group at 6h and 12h, but there was no difference between groups in nausea or pruritus treatments. Respiratory depression or significant sedation did not occur. Conclusion The dose–response relationship of intrathecal morphine for multimodal post-cesarean analgesia suggests that 50μg produces analgesia similar to that produced by either 100μg or 150μg.