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 < or = 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 microg/ml (n = 38), bupivacaine with sufentanil 1 microg/ml (n = 33), or bupivacaine with sufentanil 1.5 microg/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 < or = 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 microg/ml, 1 microg/ml, and 1.5 microg/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 0.009% wt/vol (95% CI, 0-0.023), respectively.
Conclusions: This study showed a significant (P < 0.0001) dose-dependent reduction in the MLAC ofbupivacaine by sufentanil.