DOSE-DEPENDENT REDUCTION OF THE MINIMUM LOCAL ANALGESIC CONCENTRATIONOF BUPIVACAINE BY SUFENTANIL FOR EPIDURAL ANALGESIA IN LABOR

Background The minimum local analgesic concentration (MLAC) has been d efined as the median effective local analgesic concentration in a 20-m l volume for epidural analgesia in the first stage of labor. The aim o f 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 epidura l analgesia were allocated to one of four study groups. After a lumbar epidural catheter was placed, study participants received 20 ml bupiv acaine (n = 38), bupivacaine with sufentanil 0.5 mu g/ml (n = 38), bup ivacaine with sufentanil 1 mu g/ml (n = 33), or bupivacaine with sufen tanil 1.5 mu g/ml(n = 38). The concentration of bupivacaine was determ ined by the response of the previous patient using up-down sequential allocation. The analgesic efficacy was assessed using 100-mm visual an alog pain scores, with less than or equal to 10 mm within 30 min defin ed 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, 0.0 30- 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 su fentanil.