Comparison of Fentanyl-bupivacaine and Clonidine-bupivacaine for Breakthrough Pain in Advanced Labor in Patients With Continuous Epidural Analgesia

Epidural analgesia is a popular choice among patients for relief of severe pain associated with labor and delivery. Currently, at the investigators' institution the investigators use a continuous infusion of low dose local anesthetic and narcotic (12 ml/hr of 0.0625% bupivacaine with 2 micrograms/ml fentanyl) after the initial spinal or epidural dose to maintain patient comfort until delivery. This dose of the infusion is chosen because it often provides adequate comfort without interfering with the mobility of the patient and her ability to effectively push during delivery. However, this low-dose epidural infusion strategy often results in recurrence of pain after an initial pain-free period. This recurring pain is known as breakthrough pain and is alleviated by administering small boluses of analgesics via the epidural catheter.

The pain occurring in labor is initially of visceral origin and is mediated by pain fibers originating from the low thoracic and upper lumbar segments of the spinal cord. As labor progresses to the late first phase (also known as transitional stage), pain sensations originating from the distension of the pelvic floor, vagina and perineum adds a somatic component to labor pain. This type of breakthrough pain, mediated by nerve fibers originating from the sacral nerves at dermatomes S2-S4, is often difficult to treat. Patients may experience inadequate analgesia even after boluses of analgesics are administered. Inadequate analgesia is deleterious due to subjective discomfort with its associated neurohumoral and physiological changes, and can be an initiator of the urge to bear down (push). Pushing before complete dilation of the cervix may lead to swelling, cervical injury and premature exhaustion of the mother. Adequate pain control will allow the cervix to fully dilate and motivate the mother to push effectively at the appropriate time. Although requests from patients to alleviate late stage breakthrough pain are common, there are no established data in the literature regarding the most effective strategy for pain management in this stage of labor.

This study is designed to compare the efficacy of two treatments for controlling late first stage breakthrough pain during labor: clonidine-bupivacaine versus fentanyl-bupivacaine. Both strategies are used at Columbia University Medical Center (CUMC) in this clinical situation, and there is no clear evidence whether one is superior.