Analgesia, pruritus, and ventilation exhibit a dose-response relationship in parturients receiving intrathecal fentanyl during labor.

UNLABELLED: Several studies have characterized the 50% and 95% effective doses (ED50 and ED95, respectively) of intrathecal sufentanil for labor analgesia. Few have investigated these same criteria for the less expensive alternative, fentanyl. In addition, the ventilatory effects of intrathecal fentanyl at clinically relevant doses are unclear. We performed this study to establish the dose-response relationship of intrathecal fentanyl for both analgesia and ventilatory depression. Ninety parturients in active early labor (< or = 5 cm dilation) received intrathecal fentanyl 5, 7.5, 10, 15, 20, or 25 micrograms in a double-blinded, randomized fashion (n = 15 patients in each group). Parturients were monitored for degree of pain (measured using a 100-mm visual analog pain scale), blood pressure, arterial oxygen saturation (SaO2), respiratory rate, ETCO2, and fetal heart rate 0, 1, 5, 10, 15, 20, 25, and 30 min after the administration of intrathecal fentanyl. An absolute visual analog pain scale score < or = 25 mm was defined a priori as analgesic success. The percentage of parturients who achieved analgesic success was used to construct quantal dose-response curves, from which the ED50 and ED95 values were derived for the total population (mixed parity) and the nulliparous and multiparous subpopulations separately. Overall ED50 and ED95 values (95% CI) were 5.5 (3.4-7.2) and 17.4 (13.8-27.1) micrograms, respectively. Nulliparous values were lower (5.3 and 15.9 micrograms, respectively) than multiparous values (6.9 and 26.0 micrograms, respectively) but were within the 95% CIs of the total population. Pruritus incidence in parturients with analgesic success displayed a dose-response relationship identical to that seen for analgesia. ETCO2 displayed a dose-related increase, particularly at doses > or = 15 micrograms, without concomitant changes in respiratory rate or SaO2, which suggests a decrease in tidal volume. Even in the absence of overt signs or symptoms of somnolence, intrathecal fentanyl at doses within the effective analgesic range induced a change in ventilation that may last longer than the 30-min period we studied. IMPLICATIONS: Intrathecal fentanyl induces rapid and satisfying dose-dependent analgesia in early labor; however, it also produces dose-related decreases in ventilation in the absence of overt somnolence.

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 micrograms or sufentanil 5, 10, 15, 20, or 25 micrograms 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 micrograms and 50 micrograms 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.