THE EFFECT OF EPIDURAL FENTANYL ON THE MINIMUM LOCAL ANALGESIC CONCENTRATION OF EPIDURAL CHLOROPROCAINE IN LABOR

The minimum local analgesic concentration (MLAC) has been defined as t he median effective local analgesic concentration (EC(50)) in a 20-mL volume in the first stage of labor. The aim of this study was to deter mine the local anesthetic sparing efficacy of epidural fentanyl by its effect on the MLAC of chloroprocaine. Fifty-six parturients, not exce eding 7 cm cervical dilation, who requested epidural analgesia were al located to one of two groups in this double-blind, randomized, prospec tive study. After placing a lumbar epidural catheter, 20 mt of the sol ution being tested was given: chloroprocaine (n=28) or chloroprocaine with fentanyl 3 mu g/mL (60 mu g) (n=28). The concentration of chlorop rocaine was determined by the response of the previous patient to a hi gher or lower concentration using up-down sequential allocation. Analg esic efficacy was assessed using 100-mm visual analog pain scores with 10 mm or less within 30 min defined as effective. The MLAC of chlorop rocaine was reduced from 0.43% wt/vol to 0.26% wt/vol by fentanyl (P=0 .023). Thus, the addition of epidural fentanyl 3 mu/mL (60 mu g) resul ted in a significant 40% reduction in the MLAC of chloroprocaine in th e first stage of labor.