Effects of Analgesic Techniques on Duration of Spontaneously Laboring Patients

At the first request for neuraxial labor analgesia, the cervix will be examined. If < 4.0 cm, the patient will be randomized to either Combined spinal epidural (CSE) technique with intrathecal fentanyl, CSE technique with intrathecal bupivacaine and fentanyl, or epidural de novo technique.

Labor analgesia will be administered in the sitting position, at either the L2-3 or L3-4 interspace. All patients will receive a 500mL intravenous bolus of Lactated Ringer's solution. The epidural space will be located using the loss-of-resistance technique utilizing a 17-G Tuohy epidural needle. Patients assigned to an intrathecal dose will utilize the standard needle-through-needle technique. A 19-G epidural catheter will be inserted 5 cm in the epidural space and maintenance epidural analgesia will be initiated. Patients assigned to an epidural de novo technique will have the epidural space identified with a similar loss-of-resistance technique. The epidural catheter will be inserted 5 cm into the epidural space. Epidural analgesia will be initiated with fentanyl 100mcg + bupivacaine 0.125% 10-20 mL (in divided doses). Maintenance epidural analgesia will then be initiated.

Maintenance epidural analgesia will consist of patient-controlled epidural analgesia (PCEA) with bupivacaine 0.0625% and fentanyl 1.95 mcg/mL at the following parameters: basal rate of 8 mL/hr with bolus dose = 8 mL, lock-out interval = 10 min and maximum volume = 32 mL/hr.

Breakthrough pain in all groups will be managed using anesthesiologist administered epidural boluses of bupivacaine 1.25 mg/mL, 10-15mL, without fentanyl. If instrumental vaginal delivery is required, patients will receive anesthesiologist administered epidural boluses of chloroprocaine 30 mg/mL, 5-10 mL. If a patient does not have an adequate level of analgesia or has a one-sided block, despite epidural redoses, the epidural catheter will be replaced at another level and 0.125% bupivacaine 5-15 mL will be administered until an adequate level of analgesia is established.

Because the primary outcome of the study is duration of first stage of labor, regular cervical examinations are necessary. Typically, full cervical dilation is diagnosed with a cervical examination only when the patient complains of rectal pressure, which is likely to be at a later time period in women with effective neuraxial analgesia compared to women with systemic opioid analgesia. Therefore, the duration of the first stage of labor will be artificially prolonged if regular cervical exams are not performed. The investigators intend to perform sterile cervical examinations at the first request for labor analgesia, then at routine times during the course of labor per the managing OB provider's discretion, and then every 2 hours after the patient reaches 90-100% cervical effacement until complete cervical dilation.

Fetal heart rate (FHR) tracings without information about group assignment or other treatment modalities will be assessed by a perinatologist. In addition to analyzing FHR tracings for all included participants, the investigators also plan on analyzing plasma epinephrine levels which will be drawn in each subgroup of patients.

Prior to placement of neuraxial technique, those patients included in this section of the study will have a sample of venous blood drawn. A second sample of venous blood will be redrawn 15 minutes and 30 minutes after the intrathecal dose or after initial epidural bolus. All three samples will then be analyzed for plasma epinephrine concentrations. These results will be compared with the FHR tracing analyses to see if there is any correlation.