Determination of the analgesic dose–response relationship for epidural fentanyl and sufentanil with bupivacaine 0.125% in laboring patients

Study Objective: To establish the analgesic effective doses as defined as a visual analog pain scale (VAS) of at least 10 for 95% of parturients (ED₉₅) receiving either epidural fentanyl or sufentanil with bupivacaine 0.125% for labor analgesia.

Design: Double-blind, randomized controlled study.

Setting: Two tertiary-care teaching hospitals.

Patients: 100 female patients, at full-term pregnancy, in active early labor (<5 cm cervical dilation) and requesting obstetric anesthesia services for labor analgesia.

Interventions: Patients were randomized and equally distributed to receive one of ten epidural dosing regimens of bupivacaine 0.125% alone or with either fentanyl 25, 50, 75, or 100 μg or sufentanil 5, 10, 15, 20, or 25 μg in a 10-ml bolus after a 3-ml test dose of bupivacaine 0.25%.

Measurements and Main Results: VAS scores were obtained from each parturient using a 10-cm plastic VAS slide rule at times 0, 1, 5, 10, 15, 20, 25, and 30 minutes, and then again when the patient requested additional analgesia. Analgesic duration and demographic and obstetric data also were obtained. Using a log-probit dose–response analysis, analgesic success as defined as a VAS of at least 10 with each opioid dose was plotted and an ED₉₅ value of 8 μg and 50 μg was established for sufentanil and fentanyl, respectively, in bupivacaine 0.125%. No statistical difference was detected for analgesic duration or incidence of side effects between analgesic groups.

Conclusions: Epidural analgesia with fentanyl and sufentanil in bupivacaine 0.125% behaves in a dose–response fashion allowing for the determination of equipotent dose of each.