Determining the Optimal Volume of Ropivacaine Combined with Dexmedetomidine for Programmed Intermittent Epidural Bolus in Labor Analgesia: A Randomized Dose-Response Study

Background: The programmed intermittent epidural bolus (PIEB) technique is effective for labor analgesia. Although ropivacaine combined with dexmedetomidine is used for epidural labor analgesia, the optimal PIEB volume for this regimen remains unclear. This study aimed to determine the optimal PIEB volume for effective labor analgesia using 0.0625% ropivacaine with 0.4 μg/mL dexmedetomidine. Methods: Parturients requesting labor epidural analgesia received a 20mL loading dose of 0.0625% ropivacaine mixed with 0.4μg/mL dexmedetomidine via PIEB. Eighty parturients were randomly assigned to four PIEB volume groups (6, 8, 10, or 12 mL) one hour after receiving a loading dose. Analgesia was maintained with the same formulation administered at 45-minute intervals. Effective epidural labor analgesia was defined as the absence of the need for patient-controlled or manual supplementation of analgesic medication within 6 hours after the loading dose or until full cervical dilation. Probit regression was used to estimate effective volumes. Results: A total of 79 parturients were analyzed. Effective analgesia rates in the 6, 8, 10, and 12 mL groups were 50%, 63.2%, 75%, and 100%, respectively. The estimated EV50 and EV90 were 6.5 mL (95% CI: 3.7– 7.7) and 11.0 mL (95% CI: 9.7– 14.8). A significant difference in the rate of oxytocin administration was observed among the groups (P = 0.041), with a lower rate in the 6 mL group. No significant differences were observed in adverse reactions. Conclusion: Under the conditions of this study, the EV90 for PIEB was estimated to be approximately 11.0 mL when using a solution of 0.0625% ropivacaine combined with 0.4 μg/mL dexmedetomidine for epidural labor analgesia. The use of oxytocin augmentation showed an increasing trend with higher PIEB volumes. Therefore, in clinical practice, it is advisable to strike a balance between obstetric progress and analgesic efficacy, rather than pursuing perfect analgesia.