Minimum analgesic doses of fentanyl and sufentanil for epidural analgesia in the first stage of labor

In this study, we sought to determine the minimum analgesic doses and relative potencies of fentanyl and sufentanil when they are used as the sole epidural analgesic during the first stage of labor. Nulliparous parturients (n = 66) in spontaneous labor at term gestation and requesting epidural analgesia were enrolled into this prospective, double-blinded, randomized, sequential-allocation study. Each woman received fentanyl or sufentanil diluted with 0.9% wt/vol saline to a volume of 10 mL. The initial dose was arbitrarily chosen to be 125 mug for fentanyl and 25 mug for sufentanil, with subsequent doses being determined by the response of the previous patient (testing interval, 5 mug for fentanyl and 1 mug for sufentanil). Efficacy was accepted if the visual analog score decreased to less than or equal to10 mm on a 100-mm scale within 30 min. The minimum analgesic dose or median effective dose was 21.1 mug (95% confidence interval [CI], 20.2-21.9 mug) for sufentanil and 124.2 mug (95% CI, 118.1-130.6 mug) for fentanyl (P < 0.0001). The sufentanil/fentanyl potency ratio was 5.9 (95% CI, 5.6-6.3). In conclusion, we have established the equivalent doses and relative potencies of fentanyl and sufentanil for epidural analgesia in the first stage of labor.