Pain Selective Anesthesia for Labor Mobility (PSALM Study): a Randomized Controlled Trial of Combined Lidocaine - Chlorprocaine for Labor Epidural Analgesia

The current "gold standard" epidural analgesia for labor is associated with unwanted side effects, such as motor block (affecting ambulation and the ability to push) and sympathetic blockade (causing maternal hypotension). Here, using direct clinical application of preclinical findings, the investigator assess a novel method for prolonged pain-selective anesthesia during labor avoiding motor block, sympathetic block or other neural side effects. The approach is based on the pain-selective anesthesia the investigator developed in preclinical models, where the exclusive presence of TRPV1 channels on pain fibers (nociceptors) was exploited. The investigator used polarized, membrane-impermeable local anesthetics, together with the co-administration of direct TRPV1 agonists to open TRPV1 channels, so allowing these impermeable local anesthetics to gain selective access to nociceptors. Early preclinical studies used capsaicin as the TRPV1 agonist and QX-314 as the polarized local anesthetic, but neither of these drugs are appropriate for clinical use. Here the investigators use lidocaine as the TRPV1 activator and chloroprocaine as the polarized local anesthetic and hypothesize that this co-administration will elicit pain-selective (nociceptor-specific) anesthesia for labor without side effects. Positive findings in this study will be the first evidence in humans of pain-selective local anesthesia and will be the harbinger for future studies of systemic and regional administration of these drugs for pain-selective local anesthesia for chronic and other pain states.

Inclusion Criteria: * Nulliparity * Early active labor, cervical dilatation less than 5 cm, * Age between 18 to 40, * American Society of Anesthesiologists physical status class II * Body weight less than 110 kg, * Gestational age greater than 36 completed weeks, * Singleton pregnancy * Vertex presentation. Exclusion Criteria: * Narcotic administration in the previous 3 hours * Previous uterine surgery * Pre-eclampsia * Inability to adequately understand the consent