The 50% effective dose of hydromorphone and morphine for epidural analgesia in the hemorrhoidectomy: a double-blind, sequential dose-finding study.

Background: Although previous studies have showed that epidural morphine can be used as a complement to local anesthetics for analgesia after postcesarean delivery under spinal anesthesia, there is little known about the analgesic dosage of epidural morphine and hydromorphone for hemorrhoidectomy. Therefore, we conducted this study to examine the potency ratio of hydromorphone to epidural morphine as well as effective analgesic dose for 50% patients (ED50) undergoing elective hemorrhoidectomy.

Methods: 80 patients under elective hemorrhoidectomy with combined spinal and epidural anesthesia(CSEA) in department of anesthesia, Dongguan Tungwah hospital. To assess the ED50, patients were treated with epidural morphine or epidural hydromorphone randomly using a biased coin method-determined dose with a sequential allocation procedure. Following surgery, standardized multimodal analgesia was administered to all patients. A pain response score of ≤ 3 (on a scale of 0-10) was determined to be the effective dose after 24 h following CSEA. The ED50 in both groups were determined using the probit regression and isotonic regression method. We also measured pain intensity by patient interview using a 10 point verbal numeric rating scale prospectively at 6, 12 and 24 h after CSEA, and adverse effects were also noted.

Results: The ED50 was 0.350 mg (95% CI, 0.259-0.376 mg) in hydromorphone group and 1.129 mg (95% CI, 0.903-1.187 mg) in morphine group, respectively, estimated by isotonic regression method. Regression analysis with the probit, the ED50 of epidural hydromorphone was 0.366 mg (95% CI, 0.276-0.388 mg) and epidural morphine was 1.138 mg (95% CI, 0.910-1.201 mg). Exploratory findings showed that there was no difference between the most frequent dosages of epidural hydromorphone or epidural morphine in the occurrence of nausea, vomiting and pruritus. When administered with epidural opioids at ED50 doses or higher, 97.5% (39/40) of epidural morphine patients and 97.5% (39/40) epidural hydromorphone of patients were satisfied with their analgesia.

Conclusion: Effective hemorrhoidectomy analgesia requires a 3:1 ratio of epidural morphine to epidural hydromorphone. Both drugs provide excellent patient satisfaction.