ED90 of Bupivacaine After Lidocaine Test Dose with DPE and EPL

Overview

The primary objective of our study is to use a biased coin up-down allocation methodology to estimate the dose of bupivacaine required after the lidocaine test dose to achieve initial effective comfort in 90% of patients (post test-dose ED90) via the epidural (DPE or EPL) technique in women undergoing labor induction or augmentation; the investigators hypothesize that the investigators will be able to determine the post test-dose ED90 of bupivacaine for each technique with adequate precision to inform the optimal doses to study in a subsequent randomized trial comparing the analgesic effects of DPE vs. EPL. The investigators also hypothesize that the post test-dose ED90 of bupivacaine is lower with a DPE technique than with a conventional epidural technique.

The investigators will be conducting a randomized controlled trial with patients randomized into either an EPL or a DPE group. For the first subject in the DPE and EPL techniques, the initial dose of bupivacaine 25 mg will be used, with an endpoint being the achievement of an NRS \< 3 at 30 min. Subsequent patients are administered bupivacaine doses determined by the response of the previous subject, as per the biased coin method. The subsequent up and down interval doses are bupivacaine 2.5 mg (1 mL) increments. Hence, if the first subject does not respond successfully, the dose for the second subject will be bupivacaine 27.5 mg. If the second subject does not respond successfully, the dose for the third subject will be bupivacaine 30 mg. By contrast, if a subject responds successfully, the bupivacaine dose will be decreased to 22.5 mg with a probability of 10% and maintained with a probability of 90% (ratio 1:9).