DPE Technique in Labor Epidural for Morbidly Obese Women

The primary purpose of this study is to determine differences in block quality between the "dural-puncture epidural" (DPE) and standard epidural (EPL) techniques for labor analgesia in the morbidly obese patient. The investigators hypothesize that when compared to the standard EPL, the DPE technique will improve block quality .

Study participants will be randomized by computer-generated sequence to EPL or DPE arms, stratified by class of obesity (BMI 35-39.9 kg/m2, 40\< 50 kg/m2 and ≥ 50 kg/m2) and by parity (nulliparous versus multiparous). All patients will receive a neuraxial technique in the sitting position at L3/4 or L4/5 using loss of resistance to saline. In the DPE group, a 25-g Whitacre needle will be used to puncture the dura. In both groups, the epidural catheter will be threaded 5 cm in the epidural space with an initiation dose of 15 ml of ropivacaine 0.1% with fentanyl (2 mcg/ml) over 6 minutes as per standard practice. After the initial loading dose and epidural pump is started, the blinded investigator will enter the patient's room to start data collection (time 0). Data will be collected for the first 30 minutes of epidural placement at 3,6,9,12,15,18 21, and 30 minutes to detect the time to achieve target pain ≤ 1/10, then assessed at standardized times (ever 2 hour) until delivery. Breakthrough pain will be managed by a standardized protocol. Other data to be collected will include: catheter adjustments and replacements, physician top-ups, asymmetrical block, pain score, motor block, sensory level to ice, hypotension, total anesthetic dose required, and PCEA use.

The primary outcome of this study is block quality defined by a composite of five components: (1) asymmetric block after 30 minutes of initiation, (2) top-up interventions, (3) catheter adjustments (4) failed catheter requiring replacement, and (5) failed epidural requiring general anesthesia or replacement neuraxial anesthesia for emergency cesarean section. Secondary outcomes include time to numeric pain rating scale ≤1, maternal adverse events (hypotension, fetal bradycardia, PDPH), motor block, duration of second stage of labor, total labor epidural time, total anesthetic dose required, PCEA use, and mode of delivery.

There is no increased risk/safety issue with placing a dural puncture technique than with epidural for labor analgesia.

Purpose of the study:

The primary purpose of this study is to determine if there are differences in block quality between the DPE and standard EPL techniques for labor analgesia in the morbidly obese patient. Establishing superiority of a technique is multifaceted and complex; therefore, the design of the study will define a set of measureable outcomes to assess these properties, which will be addressed in the subsequent sections. The investigators hypothesize that when compared to the standard EPL, the DPE technique will significantly improve block quality in this population.

The secondary purpose of the study is to find an optimal maintenance regimen for epidural analgesia in the morbidly obese population. For the maintenance of epidural analgesia, it is common practice to use either continuous epidural infusion or a programmed intermittent bolus using a solution of ropivicaine 0.1% with fentanyl (2 mcg/mL). To date, there are no randomized prospective studies that investigate maintenance regimens in the morbidly obese parturient population. What has been shown is that super morbidly obese patients have increased intra-abdominal and intracranial pressure which increases pressure in the epidural space. Because of this elevated pressure, the epidural spread is increased, resulting in higher sensory blocks than necessary for adequate labor analgesia.15 An important consequence is that the morbidly obese parturient may experience additional undesirable side effects to a labor epidural: increased respiratory function, increased incidence of hypotension, and increased motor block.

Design and procedures:

The investigators propose a prospective, double-blinded, randomized trial. According to our patient population and incidence of morbid obesity, enrollment would likely occur over a 2 to 3-year period. The investigators have a delivery rate of 3500 per year. Previous data from our institution show that at least 11% of our patients are morbidly obese. The investigators will therefore expect 800-900 morbidly obese women to deliver at our institution per year. The investigators anticipate to complete enrollment for the study in 1-2 years.

Epidural technique:

Once the patient requests a labor epidural, the usual standard of care for epidural placement will be initiated. The patient will have at least one 18g intravenous catheter and will receive 500-1000 milliliter (mL) fluid administration. Vitals will be monitored by the labor nurse, including continuous pulse oximetry, non-invasive blood-pressure monitoring, and external tocodynamometry. Anesthesia time-out will be performed by the anesthesia provider with participation from the nurse and the patient.

All patients will receive a neuraxial technique in the sitting position at L3/4 or L4/5 using loss of resistance to saline. In the DPE group, a 25-g Whitacre needle will be used to puncture the dura. In both groups, the epidural catheter will be threaded 5 cm in the epidural space with an initiation dose of 15 ml of ropivacaine 0.1% with fentanyl (2 mcg/ml) over 6 minutes as per standard practice. Labor analgesia will be maintained by programmed intermittent bolus with 6 ml of the same solution every 45 minutes starting 30 minutes after the initial dose. Patients will have patient-controlled epidural analgesia (PCEA) available with an 8 ml dose per demand, every 10 minutes, for a maximum dose of 45 ml for every hour.

Assignment of Study Cohorts:

Study participants will be randomized by computer-generated sequence to EPL or DPE arms, stratified by class of obesity (BMI ≥35\<40 kg/m2, ≥40\<50 kg/m2 and ≥ 50 kg/m2) and by parity (nulliparous versus multiparous). Patients will be assigned to one of the four study arms by computer-generated, randomized sequence in order to balance baseline characteristics across the arms. This will be a double-blinded study. After the consented and enrolled participant requests labor epidural, a study member will give the anesthesia provider a sealed envelope with study assignment. The envelope will contain the instructions for placement of epidural with wither standard EPL or DPE technique and specified maintenance regimen of either Programmed Intermittent Epidural Bolus (PIEB) or Continuous Epidural Infusion (CEI).

Protocol for Breakthrough Pain

* If the patient has uneven or unilateral level, the provider will withdrawal catheter 1cm from skin and bolus 5ml of epidural mix. As fetal heart rate allows for maternal repositioning, the patient will lay lateral position with unblocked side in the dependent position. (up to 3 catheter adjustments)
* If the patient has bilateral levels at that below T10 to ice, the patient will be administered 5 ml off epidural pump, up to 3 times in 15 minutes.
* If the patient has pain despite T10 levels, the provider will administer Fentanyl 100 mcg via epidural.
* If analgesia continues despite these interventions up to 3 times within 30-60 minutes, the attending anesthesiologist will determine if epidural catheter needs replacement.

Eligibility Criteria:
Inclusion Criteria:

* Women admitted to the Duke Birthing Center for spontaneous or induced vaginal delivery will be screened. After usual consultation with the anesthesia team is completed and consent for anesthesia services are obtained, eligible patients will be approached to by a member of the study team.
* ages 18-45
* singleton
* vertex fetuses at 37-41 weeks' gestation
* nulliparous and multiparous women
* cervical dilation of 2-7cm
* BMI ≥ 35 kg/m2,
* pain score \> 4
* English-speaking ability.

Exclusion Criteria:

* chronic opioid use
* Major cardiac disease
* contraindications to regional anesthesia