Drug Concentration and Volume on Adequate Labor Analgesia With PIEB
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. Pain during the first stage of labor is primarily
 due to lower uterine segment and cervical stretching. The pain signals enter the spinal cord
 through sensory nerves at the T10 through L1 dermatomes. Pain signals from the late first
 state and second stage of labor also arise from the vagina and perineum. These signals travel
 with the pudendal nerve and enter the spinal cord at S2-S4. Thus, 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.

 The optimal method for maintaining labor analgesia is unknown. Several studies have
 demonstrated that PIEB, in combination with PCEA, provide superior maintenance of labor
 analgesia (less need and longer time to provider intervention, lower local anesthetic
 consumption, less motor block, and improved patient satisfaction scores) than maintenance
 with a continuous infusion with PCEA.The mechanism for this difference is not known; however,
 one suggested mechanism is improved spread of the local anesthetic within the epidural space.
 Kaynar et al. injected methylene blue dye through a multi-orifice catheter using either a
 continuous infusion or intermittent bolus and the area of diffusion was measured on a piece
 of paper. The authors found that intermittent boluses were associated with a greater surface
 area of diffusion than continuous infusion. In a cadaver study, dye was injected into the
 lumbar epidural space, and cryomicrotome sections were taken.Dye flowed in rivulets through
 small channels in the epidural space, as opposed to moving as a unified front. The authors
 found dye injected at high pressures had more uniform spread through the epidural space,
 supporting the concept of intermittent epidural injection providing superior analgesia.

 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. Recently we completed a double-blinded randomized
 control trial evaluating two bolus delivery rates, hypothesizing that those patients
 randomized to receive higher bolus delivery rates would have improved labor analgesia.
 However, no difference was found between groups.What is more, both groups had a mean cephalad
 sensory level to cold of T6. This sensory level is higher than the traditional goal of T10
 (upper dermatome level of uterine innervation), but despite the adequate sensory level, a
 large number of patients required supplemental physician-delivered boluses of local
 anesthetic during labor. Forty percent of the women in the high-rate group and 36% of the
 low-rate group required a manual re-dose during labor. This suggests that either a higher
 volume, or higher concentration of local anesthetic (i.e., higher dose) is needed to maintain
 adequate 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).
Inclusion Criteria:

 -  18 years and above

 -  Nulliparous parturients

 -  Present to the labor and delivery unit for an induction of labor or who are in
 spontaneous labor

 -  Request neuraxial labor analgesia at ≤5 cm cervical dilation

 Exclusion Criteria:

 -  Patients who are not eligible to receive a combined spinal epidural (CSE) technique
 with 25 mcg of intrathecal fentanyl

 -  Non-English speaking

 -  Failed initiation of CSE analgesia (VAS pain score >10 15 minutes after intrathecal
 dose)

 -  Need to have the epidural catheter replaced during labor

 -  Who deliver within 90 minutes of initiation of labor analgesia

 -  Require re-dose within 90 minutes of initiation of labor analgesia.