Why is nitrous oxide for pain relief unavailable to most women giving birth in the United States when it is available in so many other countries? Most U.S. women also lack access to many nonpharmacologic methods to cope with labor pain that, although less effective than epidural analgesia, provide sufficient and satisfactory pain relief to a significant proportion of the women who use them during labor.

Labor pain is a subjective, multidimensional, and highly individualized response that occurs in the context of a particular woman’s physiology and psychology. Her own and her family’s beliefs, expectations, and values, as well as the environment in which she labors are all involved, and, in turn, her response to pain is affected by the beliefs, expectations, and values of her health care providers (1). Personal expectations, caregiver support, the quality of the practitioner-patient relationship, and the woman’s involvement in making decisions about her care can override many other factors that influence satisfaction, including pain (2). With such variation in women’s experiences of, and attitudes toward, labor pain, providing a single highly effective but expensive and intrusive analgesic, such as an epidural, is simply not enough.

In the context of obstetric analgesia, “nitrous oxide” usually refers to a half-and-half combination of oxygen and nitrous oxide gas, called by the trade name “Nitronox” (in the United States) and “Entonox” (in the United Kingdom). It is self-administered by the laboring woman using a mouth tube or face mask, when she determines that she needs it, about a minute before she anticipates the onset of a strong contraction until the pain eases (3). Its use can be started and stopped at any point during labor, according to the needs and preferences of the woman. It takes effect in about 50 seconds after the first breath and the effect is transient—essentially gone when no longer needed (3). That is an enormous advantage over epidurals for women who want to have an unmedicated birth but may need help at some point during labor and want whatever method they use to be under their control.

Although nitrous oxide provides much less complete pain relief than an epidural, it is enough for many women. It is eliminated through the lungs rather than the liver, and so does not accumulate in the mother’s or baby’s body. Unlike opioids, it does not depress respiration. If the absolute rule of self-administration is violated by someone who attaches or holds the mask to the woman’s face, and the woman becomes groggy or even unconscious, a few breaths of room air or oxygen resolve the problem quickly. Fifty percent nitrous oxide with oxygen does not cause newborns to be groggy (3).

Routine co-interventions associated with use of epidurals (intravenous lines, frequent blood pressure monitoring, mandatory continuous electronic fetal monitoring) are not needed with nitrous oxide, nor is the more frequent use of many others (Pitocin augmentation, urinary bladder catheterization, and the need for either a cesarean section or use of forceps or vacuum to achieve a vaginal delivery, replete with an episiotomy and, not infrequently, the subsequent need to repair a 3rd or 4th degree laceration) (4,5).

A recent U.S. survey based on interviews with a representative sample of nearly 1,600 women who gave birth in American hospitals in 2005 provides information on use of 5 pharmacologic and 9 nonpharmacologic pain-relief methods used by women during childbirth in U.S. hospitals during that year (6). The 4 pharmacologic methods used by women who gave birth vaginally were epidural or spinal analgesia (71%), parenteral narcotics (24%), nitrous oxide (1%), and pudendal or other local block injections (1%) (C. Sakala, personal communication; unpublished data, December 4, 2006). Many women used more than 1 pharmacologic method during labor, and 14 percent used no pain medication at all (7). Use of epidural or spinal analgesia by all women (vaginal plus cesarean births) increased from 63 percent in the first survey (data collected from mid-2000 to mid-2002), to 76 percent in 2005 (7). Inversely, nonuse of any pain medication fell from 20 percent in the first survey to 14 percent in 2005. The 9 nonpharmacologic methods were all used more often than nitrous oxide.

By comparison, nitrous oxide is used by the majority of women in many countries that are relatively similar to the U.S. in general socioeconomic and medical standards. Nitrous oxide was used by 48 percent of the women who gave birth in Finland in 2005 (8), and 46 percent of those who gave birth in New South Wales, the largest state in Australia, in 2004 (down from 49% in 2000) (9).

In Canada, 43 percent of women who gave birth in hospitals in British Columbia during 2004/2005 used nitrous oxide alone or in combination with other methods of pain relief, a decline of more than 2 percent since 2000/2001 (M. Klein, personal communication; data from C. Johnson, Provincial Perinatal Analyst, British Columbia Reproductive Care Program, October 30, 2006). The use of nitrous oxide was highest (50%) among women who labored in hospitals with the highest volume of births per year, and lowest (22%) in hospitals with fewer than 10 births per year, a finding that contradicts the idea that its use is higher in hospitals that cannot provide 24-hour-a-day-every-day-of-every-week access to epidurals. Nitrous oxide can also be taken to home births by midwives in British Columbia, although few carry it with them, since “most of our homebirth women are very committed and do fine without any drugs” (K. Campbell, Division of Midwifery, University of British Columbia, personal communication, October 1, 2006).

Based on data from a sample of women who gave birth in 8 locations within the United Kingdom in 2000, approximately 62 percent used nitrous oxide (J. Green, personal communication, October 8 and December 1, 2006; unpublished data from the 2000 Greater Expectations study, Mother & Infant Research Unit, University of Leeds). Forty-two percent of women who used nitrous oxide also used parenteral Demerol or other narcotics (Pethidine, meperidine), 31 percent used transcutaneous electrical nerve stimulation (TENS), and 33 percent used epidural analgesia. Twenty-one percent of the entire sample used nitrous oxide but none of the 3 other methods. Including all women who used nitrous oxide, 38 percent judged it to be “very effective,” 47 percent only “partly effective,” and 15 percent “not effective at all”; 68 percent of those who used it were very pleased. Three percent of women who used it felt that they were under considerable pressure to try it; 9 percent felt “a bit” of pressure, and 86 percent said, “No, not at all”; 1 percent of women were encouraged not to use it. Its use among first-time mothers was lower compared with those having a second or higher-order baby.

Nitrous oxide also provides a unique advantage when pain relief for a procedure is suddenly needed, such as manual removal of a placenta, vacuum extraction or forceps on a woman without an epidural, or manual rotation of an occiput posterior fetus per vagina. Nothing is as quick as nitrous oxide; in its absence some women have to endure these procedures without any pain relief (P. Simkin, personal communication, December 1, 2006).

Despite its wide and popular use in many countries, nitrous oxide for the relief of labor pain is largely unknown in the U.S., where the expanding use of epidural analgesia has resulted in an evolving epidural monoculture in some hospital obstetric units. The assumption seems to be that every woman who goes to the hospital to labor (not for a prescheduled cesarean) should have an epidural as soon as she begins to experience any pain. In such settings, women who want to avoid an epidural are asking for “special” care and may disrupt staff routines and expectations. Some women feel pressured to accept an epidural but lack access to other effective pain-management methods. A woman who wants to achieve a normal birth may find herself “between a rock and a hard place”—that is, without any satisfactory option. She certainly also lacks the autonomy and informed choice now being cited as the ethical imperative driving the concept of elective cesarean births (10).

My search into the history and use of nitrous oxide in several countries, as well as its benefits and risks (including occupational reproductive health hazards for women who work with women during labor in settings with obsolete equipment and inadequate ventilation), suggests an explanation for its very limited use in the U.S.: obstetric use of nitrous oxide in America is similar to that of any older, inexpensive, off-patent, unglamorous, safe and reasonably effective but not highly potent drug. Nitrous oxide is like an “orphan” drug—little known, outside of dentistry, lacking élan and pizzazz, with no companies or influential professional groups that stand to profit by its greater use.

Some obstetricians and hospitals are afraid to use it because of the possible risk of environmental contamination and occupational hazard. But modern American hospitals are well ventilated, and modern equipment for the administration of nitrous oxide “scavenges” the unused gas (3). As with the use of many other potentially hazardous substances, hospitals must establish safe practices and train their staff to use them. Preventing the use of nitrous oxide for women during labor out of concern about environmental hazards is a conspicuous red herring.

Although nitrous oxide is a natural adjunct to the midwifery model of care, few American midwives have had any experience with it, and its use is not taught in midwifery educational programs. Natural childbirth supporters are not attracted to it because it is a drug (but not a narcotic!). But among the few American women who have used it in other countries or in U.S. hospitals that have since discontinued its use, some have become greatly disturbed when they learn that it is not available.

Nitrous oxide has significant cost advantages. It is much simpler and less expensive to use than epidural analgesia and does not result in complications that require additional treatments and both mother and baby days of hospitalization. It should be attractive to those concerned about the extremely high cost of health care in the United States, where clogged coronary arteries and pregnancy were reported to be the two most expensive conditions contributing to $790 billion in annual hospital costs (11). The care of pregnant women was the biggest cost for private insurance companies and Medicaid in 2004.

My intent in writing this editorial is to issue a challenge to U.S. midwives and midwifery educators to become informed about nitrous oxide, to natural childbirth leaders to consider its benefits versus the current options for women who want to achieve a spontaneous vaginal birth in U.S. hospitals, and to all who support the concept of a pregnant woman’s right to autonomy and informed choice about major elements of her care during childbirth.


  1. Top of page
  2. Acknowledgments
  3. References

I am very grateful for the help of Michael Klein, Canada; Josephine Green, United Kingdom; Sally Tracy, Australia; and Mika Gissler, Finland, for providing information and, in some cases, special analyses of unpublished data on the use of nitrous oxide in their countries. I also wish to thank Penny Simkin, Carol Sakala, and Mark Rosen, for their valuable information and assistance in the United States.


  1. Top of page
  2. Acknowledgments
  3. References
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    Lowe, NK. The nature of labor pain. Am J Obstet Gynecol 2002;186(5):S1624.
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    Hodnett ED. Pain and women’s satisfaction with the experience of childbirth: A systematic review. Am J Obstet Gynecol 2002;186(5):S160172.
  • 3
    Rosen MA. Nitrous oxide for relief of labor pain: A systematic review. Am J Obstet Gynecol 2002;186:S110126.
  • 4
    Mayberry LJ, Clemmens D, Anindya D. Epidural analgesia side effects, co-interventions, and care of women during childbirth: A systematic review. Am J Obstet Gynecol 2002;186:S8193.
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    Lieberman I, O’Donoghue C. Unintended effects of epidural analgesia during labor: A systematic review. Am J Obstet Gynecol 2002;186:S3168.
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    Declercq ER, Sakala C, Corry MP, Applebaum S. Listening to Mothers II: Report of the Second National U.S. Survey of Women’s Childbearing Experiences. New York: Childbirth Connection, October 2006:3133.
  • 7
    Declercq ER, Sakala C, Corry MP, et al. Listening to Mothers: Report of the First National U.S. Survey of Women’s Childbearing Experience. New York: Childbirth Connection, October 2002:1823.
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    STAKES. Official Statistics of Finland, Health 2006: Statistical Summary 18/2006. Available at:; accessed December 2, 2006.
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    NSW Department of Health. New South Wales Mothers and Babies 2004. December, 2005:25. Available at:; accessed September 26, 2006.
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    Minkoff H. The ethics of cesarean section by choice. Semin Perinatol 2006;30(5):309312.
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    U.S. Agency for Healthcare Research and Quality, HCUP Statistical Brief #13. The National Hospital Bill: The Most Expensive Conditions, by Payer, 2004. Available at: (PDF file, 307 KB; HTML); accessed December 2, 2006.