US Midwives' Knowledge and Use of Sterile Water Injections for Labor Pain

Lena Märtensson, CNM, PhD; Maureen McSwiggin, CNM, MS; Judith S. Mercer, CNM, DNSc

Disclosures

J Midwifery Womens Health. 2008;53(2):115-122. 

In This Article

Background

Methods to lessen labor pain are a major concern for the mother and her caregivers. Different sensory stimulation methods can be good alternatives for pain relief in labor. Examples of these techniques include massage, counter-pressure, heat, acupuncture, and sterile water injections. Sterile water injections are subcutaneous or intracutaneous injections of a small amount of sterile water administered in the lumbar-sacral region of the back[3] (see Table 1 , Figure 1, and "Sample Procedural Guidelines for Sterile Water Injections"). By introducing small amounts of sterile water into the intradermal layer of skin, a hyperstimulation of the large inhibitory nerve fibers occurs.[1] There is a sharp, transitory stinging sensation within the first seconds of application, which is more pronounced when the injections are given intracutaneously.[4] The onset of pain relief is fast -- usually within a few minutes -- and can last 1 to 2 hours. The treatment can be repeated several times.[1]

Figure 1.

Diagram of suggested sites for sterile water injections if one is not using maternal pain points. (Reprinted with permission from Märtensson, 2006.[3])

The technique for sterile water injections is very old. It was first mentioned in the literature by Halsted[5] in 1885 when he wrote, "The skin can be completely anesthetized to any extent by cutaneous injections of water." In 1904, Anon[6] stated that sterile water could be used as a local anesthetic during minor surgery. The method was considered difficult because of the discomfort from administration, but could nevertheless constitute a good alternative for those patients with hypersensitivity to the drugs used with general anesthesia. Sterile water injections have been used for treatment for pain other than labor pain with positive outcomes, including acute attack of urolithiasis[7] and neck and shoulder pain after whiplash injury.[8,9] However, the majority of the recent literature about sterile water injections addresses lower back pain during labor.

Several studies have consistently shown that sterile water injections provide good pain relief during labor, particularly for low back pain[3,10,11,12,13,14,15,16,17,18] ( Table 1 ). The trials are quite similar to each other regarding aims, designs, instruments, and results. The only negative side effect is the burning or stinging pain the woman experiences in connection with administration. Some studies indicate that the burning sensation can be reduced if the injections are given subcutaneously[4] without losing the pain-reducing effect.[11,15] In three systematic reviews, the authors concluded that sterile water injections were more effective for labor pain than acupuncture and other complementary methods, such as acupressure, hypnosis, and massage.[19,20,21]

The nature of labor pain is a complex process. The pain experience of childbirth is extremely individual, and it also changes throughout the labor process.[22] Pain is considered to have at least three dimensions: sensory, affective, and cognitive components.[23,24] The sensory component passes signals from different stimuli all over the body to the brain in an attempt to give information about the intensity, quality, and location of pain.[25] The affective component is associated with pleasant or unpleasant emotions.[26,27] For labor, fear and anxiety are important emotions that can enhance pain.[28,29,30,31] The cognitive component is associated with knowledge about mood, behavior, and thought patterns.[32] Knowledge about all these components helps in understanding an individual's response to pain.[33]

The mechanisms of action for sterile water injections are not fully clear, but the Gate Control Theory is one logical explanation. This theory was formulated by Melzack and Wall in 1965.[2] It describes pain as a function of the balance between the information traveling into the spinal cord through large nerve fibers and information traveling into the spinal cord through small nerve fibers. If the relative amount of activity is greater in small nerve fibers, then there will be pain. However, if there is more activity in the large nerve fibers, there should be little or no pain as these fibers cause the pain "gate" to close to other stimuli. For example, when the skin in the lumbar area is stimulated with sterile water injections, a cutting type of pain will be generated, thus creating a block to the slower signals from the uterine contractions. This knowledge is useful to practitioners assisting women in labor, because many techniques for labor support depend on the distraction from pain caused by the stimulation of competing nerve fibers. Methods such as massage, counter-pressure, acupuncture, and heat may have a mechanism of action similar to sterile water injections.

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