To estimate the dose of bupivacaine required to achieve initial effective comfort in 90% of patients (ED90) via the epidural (DPE or EPL) technique in women undergoing labor after receiving a lidocaine "test dose"

The primary objective of our study is to use a biased coin up-down allocation methodology to estimate the dose of bupivacaine required to achieve initial effective comfort in 90% of patients (ED90) via the epidural (DPE or EPL) technique in women undergoing labor induction or augmentation; we hypothesize that we will be able to determine the ED90 of bupivacaine for each technique with adequate precision to inform the optimal doses. We will be conducting this study in women who receive a prior lidocaine "test dose" used in standard clinical practice

Inclusion Criteria:

• Parturient with no major co-morbidities
• Singleton, vertex gestation at term (37-42 weeks)
• Less than or equal to 5 cm dilation
• Desire to receive epidural labor analgesia
• Numerical Rating Scale greater or equal to 5 (NRS 0-10, where 0 = no pain, and 10 = worst pain imaginable), at time of epidural labor analgesia request.

Exclusion Criteria:

• Current or historical evidence of clinically significant disease or condition, including diseases of pregnancy (i.e preeclampsia, gestational diabetes)
• Any contraindication to the administration of an epidural technique
• History of hypersensitivity or idiosyncratic reaction to an amide local anesthetic agent
• Current or historical evidence of a disease which may result in the risk of a cesarean delivery (i.e. history of uterine rupture). NB: Exception-trial of labor after cesarean delivery (TOLAC) will be eligible.
• Evidence of anticipated fetal anomalies

The biased-coin allocation after each successful response will be implemented by flipping a virtual biased coin (10% vs. 90% probability of randomizing the next patient to the lower vs. same dose than received by the last patient with the same epidural technique) using R statistical software (R Foundation for Statistical Computing, Vienna, Austria). Care Provider (Clinical Anesthesiologist) will administer the identified dose, then summon blinded observer.