Determination of Median Effective Concentration (EC50) of Ropivacaine with Adjuvant Dexmedetomidine When Using the Dural Puncture Epidural Technique for Labor Analgesia: An Up-Down Sequential Allocation Study

Background: The dural puncture epidural (DPE) technique offers a promising option for managing labor pain. While dexmedetomidine has proven clinically efficacious in labor pain, its optimal concentration in DPE technique remains underexplored. This trial was designed to identify the ideal adjuvant concentration of dexmedetomidine to ropivacaine in the DPE technique for labor analgesia. Methods: Parturients were randomly allocated to six groups receiving different concentrations of dexmedetomidine (0, 0.1, 0.2, 0.3, 0.4, and 0.5 μg/mL). In each group, ropivacaine was initiated at 0.1% concentration. Effective analgesia was defined as visual analog scale scores ≤ 3 during two consecutive uterine contractions within 30 minutes; if achieved, the ropivacaine concentration for subsequent parturients was reduced by 0.01%, otherwise increased by 0.01%. Results: The median effective concentrations of ropivacaine at dexmedetomidine concentrations of 0.3, 0.4, and 0.5 μg/mL were 0.042% (95% CI: 0.035%-0.049%), 0.036% (95% CI: 0.030%-0.043%), and 0.037% (95% CI: 0.030%-0.044%), which were lower than those at 0, 0.1, and 0.2 μg/mL (0.079% [95% CI: 0.071%-0.088%], 0.070% [95% CI: 0.062%-0.078%], and 0.059% [95% CI: 0.053%-0.066%]). Comparisons between the three highest dexmedetomidine doses showed no significant differences. Scores on the Ramsay Sedation Scale were significantly elevated in the three highest concentration groups compared to the 0 and 0.1 µg/mL groups. Additionally, the scores for the 0.3 and 0.5 µg/mL groups exceeded that of the 0.2 µg/mL group. Comparisons involving the 0.2 µg/mL group versus the 0.4 µg/mL group, as well as those among the three highest concentration groups, all showed no statistical difference. Conclusion: For labor analgesia using the DPE technique, 0.3 µg/mL dexmedetomidine is the optimal adjuvant concentration to ropivacaine, balancing analgesic efficacy and safety. Higher concentrations do not enhance analgesia but may increase the risk of sedation.