Determination of the ED95 for intrathecal plain bupivacaine combined with fentanyl in active labor.

Background: Combined spinal-epidural (CSE) analgesia is an effective technique for pain control in labor and is particularly useful in the active phase. Excessive doses of intrathecal bupivacaine may be associated with adverse effects. This study is designed to estimate the ED95 for intrathecal plain bupivacaine with fentanyl 15 microg in labor.

Methods: Forty healthy women in active labor (cervical dilatation > or = 5 cm and verbal numeric pain score > or = 6/10) were given CSE for labor analgesia with intrathecal plain bupivacaine and fentanyl 15 microg. The initial dose of bupivacaine was 1.75 mg. Doses were varied in a 0.25-mg testing interval according to a method of sequential allocation designed to cluster the dose around the ED95. Effectiveness was defined as a verbal numeric pain score < or = 1 within 10 min of intrathecal injection.

Results: There was a 100% response rate to the 1.75-mg dose (95% CI 84.6-100.0%) and an 85.0% response rate to 1.50 mg (95% CI 64.0-95.8%). The ED95 for intrathecal plain bupivacaine with fentanyl 15 microg in active labor was 1.66 mg (95% CI 1.50-482.5 mg). The incidence of fetal bradycardia was 7.5%. The incidence of pruritus was 55%. No patient experienced motor block.

Conclusions: This is the first dose-finding study specifically designed to estimate the ED95 of intrathecal bupivacaine combined with a fixed amount of fentanyl for analgesia in active labor. The combination of bupivacaine 1.75 mg with fentanyl 15 microg rapidly and reliably alleviated pain in the active phase of labor.