Dose–response of intrathecal morphine when administered with intravenous ketorolac for post-cesarean analgesia: a two-center, prospective, randomized, blinded trial

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 200–300 μg 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 12 mg, fentanyl 15 μg and a randomized dose of 50, 100, or 150 μg morphine in a volume of 2.2 mL. Patients received intravenous ketorolac 30 mg before leaving the operating room and 15 mg intravenously every 6 h for the duration of the study (24 h). All received postoperative patient-controlled intravenous morphine. The primary endpoint was total intravenous morphine administered postoperatively over 24 h, analyzed using mixed model regression. Results There were no differences between dose groups (or institutions) in intravenous morphine use over 24 h. Visual analog scale scores for pain and nausea did not differ. Pruritus was greater in the 100 and 150 μg groups than the 50 μg group at 6 h and 12 h, 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 50 μg produces analgesia similar to that produced by either 100 μg or 150 μg.