Low-dose epidural morphine for postpartum pain relief: a randomized, single-blind study.

Introduction: Epidural morphine administration following vaginal delivery reduces postpartum pain; however, side effects may occur. We investigated whether a lower dose could achieve pain relief without increasing the incidence and severity of side effects.

Methods: Eighty women treated with combined spinal-epidural analgesia received 0.75 mg epidural morphine (morphine group) or normal saline (normal saline group) after delivery. The primary outcome was the area under the curve (AUC) of the visual analog scale score assessing perineal and contraction pain for 24 h following delivery. Secondary outcomes were time until initial request for additional analgesics, number of analgesic medications, and side effects incidence and severity.

Results: The morphine group did not show lower mean AUCs for postpartum perineal (290, interquartile range [IQR]: 90-580 vs 450, IQR: 265.6-760; P = 0.07) or contraction pain (18.8, IQR: 0-105 vs 156.3, IQR: 11.5-300; P = 0.004). The time until the initial request for additional analgesics was longer in the morphine group (530 min, 95% confidence interval [CI]: 365 to 915 min vs 268 min, 95% CI: 230 to 385 min; P = 0.001). The median (IQR) number of analgesic medications within 24 h were 2 (0.5-3) and 2.5 (2-3) in the morphine and saline groups, respectively (P = 0.007). There were no differences in the incidence of side effects between the groups.

Conclusions: Epidural morphine following vaginal delivery reduces contraction pain but not perineal pain and prolongs the time until initial request for additional analgesia without increasing side effects.

Clinical trials registration number: The University Hospital Medical Information Network Clinical Trials Registry (registration number: UMIN000039351).