Drug Concentration and Volume on Adequate Labor Analgesia With PIEB

Neuraxial labor analgesia is performed by the administration of a local anesthetic/opioid mixture in the epidural space. The delivery method is a combination of continuous infusion, provider-administered boluses and patient-administered boluses (patient controlled epidural analgesia \[PCEA\]) via epidural catheter. The anesthetic solution administered through the lumbar epidural catheter must spread cephalad in the epidural space to reach the T10 nerve roots and spinal cord, and must spread caudad to reach the caudal nerve roots in the epidural space. Epidural infusion pumps capable of delivering PIEB of local anesthetic with PCEA have become commercially available and many studies have attempted to assess the optimal parameter settings (including volume of programmed bolus, bolus interval, rate of bolus administration) to provide superior labor analgesia. Traditionally higher concentration local anesthetic solutions have been associated with increased motor blockade leading to a higher incidence of instrumental vaginal delivery. Several local anesthetic solutions with varying drug concentrations are available for labor analgesia and are used clinically in the United States. We plan to perform a randomized, controlled, double-blind study to test the hypothesis that patients whose labor analgesia is maintained using PIEB with low-volume bolus (6.25 mL) of a higher local anesthetic concentration solution (0.1% bupivacaine with fentanyl 2.0 mcg/mL) will require less supplemental analgesia (manual provider re-doses) than patients whose PIEB is delivered with a high-volume bolus (10 mL) of lower density local anesthetic solution (0.0625% bupivacaine with fentanyl 2.0 mcg/mL). The aim of this study is to evaluate the association between bolus volume and concentration of local anesthetic during maintenance of labor analgesia with programmed intermittent epidural bolus (PIEB) analgesia. The hypothesis of this study is: patients whose labor analgesia is maintained using PIEB with low-volume bolus (6.25 mL) of higher local anesthetic concentration solution (0.1% bupivacaine with fentanyl 2.0 mcg/mL) will have a longer duration of adequate analgesia (time to first manual re-dose request) than patients whose PIEB is delivered with a high-volume bolus (10 mL) of lower concentration local anesthetic solution (0.0625% bupivacaine with fentanyl 2.0 mcg/mL).