Sterile Water Injection for Labor Pain

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.