Dose-response of epidural ropivacaine with 0.4 μg mL-1 of dexmedetomidine for labor analgesia: A prospective double-blinded study

Background: Studies have shown that the ideal dose of epidural dexmedetomidine is 0.4 mu g mL(-1) for epidural labor analgesia. However, the appropriate dose of ropivacaine when combined with 0.4 mu g mL-1 of dexmedetomidine for epidural labor analgesia is still unknown. Therefore, we aimed to determine the dose-response of ropivacaine when using 0.4 mu g mL-1 of dexmedetomidine as epidural adjuvant for labor analgesia. Methods: One hundred of nulliparous singleton pregnant patients were randomized allocated into 1 of 5 groups with epidural ropivacaine concentration of 0.05%, 0.0625%, 0.075%, 0.0875%, and 0.1%. Labor analgesia was initialed with 12 mL of the mixed study solution. Effective analgesia was defined as a visual analogue scale <10 mm 30 minutes after the initial epidural bolus. The EC50 and EC95 for epidural ropivacaine was calculated by probit regression. Results: Ninety-three of parturients were involved into the final analysis. Totals of 63.2% (12/19), 73.7% (14/19), 88.9% (16/18), 94.7% (18/19), and 100% (18/18) of parturients in group 0.05, 0.0625, 0.075, 0.0875, and 0.1 received effective epidural labor analgesia. The calculated EC50 and EC95 of epidural ropivacaine were 0.046% (95% CI 0.028-0.054%) and 0.086% (95% CI 0.074-0.137%), respectively. Conclusions: Under the condition of the study, a bolus of 12 mL ropivacaine 0.086% and dexmedetomidine 0.4 mu g mL(-1) could afford 95% of nulliparous singleton pregnant patients without suffering labor pain after a test dose of lidocaine 45 mg.