Determination of ED50 of hydromorphone for postoperative analgesia following cesarean delivery

Background Morphine is the most common opioid injected into the intrathecal space for postoperative analgesia following cesarean delivery, but ongoing medication shortages have resulted in limited availability. One proposed morphine alternative is hydromorphone. Studies investigating its use in post-cesarean analgesia are limited. This study was conducted to determine the median effective dose of intrathecal hydromorphone 12 h postpartum. Methods Twenty healthy women undergoing elective cesarean delivery were recruited into this study. Hydromorphone doses were determined using the up-down sequential method. The study dose of hydromorphone started at 6 μg and was raised or lowered by 2 μg depending on the 12-h efficacy of the preceding participant’s dose. Pain scores of <3/10 were considered successful and the subsequent patient received a lower dose. Participants received 0.5% bupivacaine 12.5 mg, fentanyl 25 μg, and the study dose of hydromorphone as a single intrathecal injection. Results Ten of 20 participants reported an effective hydromorphone dosage 12 h post-injection. The median effective hydromorphone dosage was 4.6 μg (95% CI 3.72 to 5.48 μg) based on participants’ reported visual analog pain scores of <3/10. No significant side effects or adverse outcomes were observed. Conclusion Intrathecal hydromorphone may be an effective alternative to morphine for post-cesarean pain management. The amount of intrathecal hydromorphone necessary to provide analgesia at 12 h postoperatively may be significantly lower than doses currently in use. Further research should be performed to identify the optimal dose of intrathecal hydromorphone for post-surgical pain relief.