Dose-dependent reduction of the minimum local analgesic concentration of bupivacaine by sufentanil for epidural analgesia in labor

Background The minimum local analgesic concentration (MLAC) has been defined as the median effective local analgesic concentration in a 20-ml volume for epidural analgesia in the first stage of labor. The aim of this study was to determine the local anesthetic-sparing efficacy of epidural sufentanil by its effect on the MLAC of bupivacaine. Methods: In this double-blind, randomized, prospective study, 147 parturients at less than or equal to 7 cm cervical dilation who requested epidural analgesia were allocated to one of four study groups. After a lumbar epidural catheter was placed, study participants received 20 ml bupivacaine (n = 38), bupivacaine with sufentanil 0.5 mu g/ml (n = 38), bupivacaine with sufentanil 1 mu g/ml (n = 33), or bupivacaine with sufentanil 1.5 mu g/ml(n = 38). The concentration of bupivacaine was determined by the response of the previous patient using up-down sequential allocation. The analgesic efficacy was assessed using 100-mm visual analog pain scores, with less than or equal to 10 mm within 30 min defined as effective, Results: The MLAC of bupivacaine alone was 0.104% wt/vol (95% CI, 0.090-0.117), The addition of sufentanil at doses of 0.5 mu g/ml, 1 mu g/ml, and 1.5 mu g/ml resulted in significant reductions (P < 0.0001) in the MLAC of bupivacaine to 0.048% wt/vol (95% CI, 0.030- 0.065), 0.021% wt/vol (95% CI, 0-0.055), and 0.003% wt/vol(95% CI, 0-0.023), respectively. Conclusions: This study showed a significant (P < 0.0001) dose-dependent reduction in the MLAC of bupivacaine by sufentanil.