Intracutaneous Sterile Water Injections

For most women, the most significant pain they will experience is the pain associated with childbirth. Up to one-third of women experience "back labor", this typically occurs when the fetus assumes varying degrees of malposition, especially the occiput posterior position, and causes additional constant pressure against the maternal spine and pelvis. "Back labor" presents as constant pain, that occurs even between contractions. It is often difficult to manage, by the patient, the obstetrician, and the anesthesiologist, and may increase the rate of instrumental and caesarian delivery.

Epidural anesthesia/analgesia is the most common and effective intervention used to help women cope with labor pain. Dilute concentrations of local anesthetic and opioid provide complete analgesia for most women. Some women, however, have breakthrough pain, often due to "back labor," and require more concentrated drug solutions. This increases the side effects associated with these drugs (e.g., hypotension, pruritus, motor block), thus treatment of this pain poses a challenge for the anesthesiologist and the obstetrician.

Sterile water injections (SWI) are a simple and well-established method of managing labor pain among midwives. This intervention was first used to alleviate pain associated with kidney stones, and was introduced to obstetrics in the 1970s. Using a syringe, small amounts of sterile water is deposited subcutaneously near the sacral area. The sterile water causes osmotic and mechanical irritation resulting in a brief (15-30 second) and significant stinging sensation. The onset of pain relief follows almost immediately and may last for up to two hours. The procedure can be repeated a number of times.

Sterile water for pain management is most often administered using four intracutaneous injections: two sites lateral to the lumbosacral spine and two sites 2-3 cm below and 1-2 cm medial to the original two injection sites. 0.1 mL of sterile water is injected between the dermal layers to raise a small bleb on the skin surface at each of the four sites. In labor, the injections are administered sequentially during a uterine contraction, with the series of four injections, performed two at a time, completed within 20-30 seconds.

The investigators hypothesize that the use of sterile water injections in women with neuraxial analgesia with breakthrough pain will result in decreased local anesthetic requirements and increase patient satisfaction.

Since it is assumed that the neuraxial anesthetic is placed prior to transition to active phase of labor, the patient will receive the intervention when they report breakthrough pain. Prior to administration of the intervention, the adequacy of the existing neuraxial anesthetic will be verified as bilateral decreased discrimination to cold from T8 to the sacrum. Four tuberculin syringes, each containing 0.1 mL of the assigned solution labeled "study drug" will be prepared. Patients allocated to the study group will receive sterile water, and those allocated to the control group will receive sterile normal saline solution.

The area to be injected will be prepared with chlorhexidine wipes to ensure sterility. In the sitting position, study subjects will receive a total of 0.4 mL of "study drug" via four injections: bilateral injections at the posterior superior iliac spine on and bilateral injections at 1 cm medial and 1-2 cm inferior to the first point.

Patients will be asked to rate their overall labor pain using a 0-100 mm visual analog scale (VAS) for pain prior to study drug administration and every 30 minutes until commencement of pushing. They will also be asked to specifically rate low back pain with the VAS. Analgesia administration data from the time of study drug injection, including maintenance epidural solution volume, time of first patient controlled epidural analgesia (PCEA) bolus request, number of PCEA bolus requests and delivered doses, total PCEA bupivacaine dose, time to first request for manual rebolus, number of manual bolus doses, manual bolus bupivacaine dose, total bupivacaine dose and total fentanyl dose.

Additional recorded data will include maternal age, height, weight, cervical dilation at initiation of neuraxial analgesia and at study drug administration, duration of labor (initiation of analgesia to delivery), maximum oxytocin infusion rate during labor, and mode of delivery. A "total labor pain score" will be assessed approximately 60 minute after delivery, as well as satisfaction with labor analgesia using a 100-mm VAS.

Eligibility Criteria:
Inclusion Criteria:

* multiparous women
* spontaneous labor
* at least 18 years of age
* presenting for vaginal delivery with cervical dilation of 4 centimeters or less

Exclusion Criteria:

* nulliparous
* less than 18 years old
* contraindication to placement of neuraxial anesthetic
* skin infection in area to be injected
* medical therapies considered to result in tolerance to opioids
* history of chronic pain (requiring regular medical follow-up with pain specialists)
* recent use of opioid analgesics (within the year preceding pregnancy)