Expanded Discussion of Nitrous Oxide for Labor Pain Relief

May 14, 2008

Last week’s post questioning why nitrous oxide isn’t more widely available to women in labor generated a lot of discussion, so we’ve decided to dedicate today’s post to exploring the issue further.

One commenter posted a response from her anesthesiologist friend, who discussed his concerns about the safety of nitrous oxide for both the laboring woman and other people in the room exposed to the gas. After reading the anesthesiologist’s concerns, Judith Rooks, a nurse-midwife, epidemiologist, and Our Bodies, Ourselves contributor, felt compelled to respond. She sent us a long, detailed email breaking down his concerns one by one, and addressing what she believes is misinformation about what is known about nitrous oxide and the risks of epidurals. We’ve decided to post the entire email here (with permission). The original comments are posted in bold, with Judith’s response immediately following.

“Nitrous oxide in trace amounts is considered a biological hazard. It must be scavenged, which is difficult to impossible for someone who has just been taught to self-administer while in labor.”

Yes, nitrous oxide (N2O) is a biological hazard, but not all biological hazards are equal. Nitrous oxide is produced by trees, among other sources, so some of it is a natural part of our environment. I mention this just so that no one thinks it is like Sarin, e.g., which is a very deadly gas even in minute quantities. N2O has been used as a component of anesthesia for more than a hundred years, and as an analgesic for women during labor for nearly a hundred years. It is the most widely used labor analgesic in the UK, Sweden, Finland, and many other countries. It is also widely used for analgesia during dentistry in this and other countries. American dentists find it particularly useful for children, and it is often used by pediatricians during necessary procedures on children.

Like all effective drugs, N2O can have ill effects, but only as a result of large doses, with dose being the product of three factors: (1) concentration, (2) duration of exposure, and (3) time for restitution between episodes of intermittent exposure. For instance, it can affect vitamin B12 metabolism resulting in health problems due to impaired cell division. But, because the effect is dose-dependent, problems are usually associated with chronic recreational abuse (addiction to recreational use of N2O) or inborn vitamin B-deficiency disorders. Healthy women using 50/50 mix of N2O & O2 during contractions are not at risk of this effect.

But it was thought to increase the incidence of infertility and spontaneous abortions among female physicians, dentists, midwives, dental hygienists and nurses exposed to N2O that leaked or was exhaled into the ambient air by patients who were using N2O. The anesthesiologist referred to a 1970s study of its effects on dental assistants. In this case, the high dose was due to prolonged and repetitive exposure to low doses. This problem has been addressed by anesthesiologists, other physicians and dentists, as well as by the National Occupational Safety and Health Agency (OSHA) by mandating the N2O only be used in well ventilated buildings (virtually all US hospitals meet this requirement) and use of scavenging equipment, which sucks nitrous oxide that is exhaled by the patient back into the equipment. (For more information, see the American Academy of Pediatric Dentistry’s policy on minimizing occupational health hazards associated with use of N2O, an American Society for Anesthesiology newsletter that reports their findings regarding occupational risk from trance anesthetic gases, and the OSHA guidelines for use of N2O .)

In 2002 Dr. Mark Rosen, an obstetric anesthesiologist at the University of California in San Francisco published an extensive review of the risks, benefits and effectiveness of nitrous oxide for analgesia during labor. The following is a quote from that paper:

“Some have suggested that occupational exposure of healthcare workers (nurses, midwives, etc.) to nitrous oxide for labor analgesia renders it an unsafe or unfeasible technique. Although the actual risks associated with occupational exposure to nitrous oxide are not precisely known, there is a very low or nonexistent causal effect of exposure to nitrous oxide or isoflurane and mutagenic, teratogenic or carcinogenic effects (62). Epidemiological studies performed in the 1970s suggested that trace levels of waste anesthetic gases, as found in operating rooms, delivery rooms, and dentist offices were hazardous. These studies were retrospective, mail questionnaire designed studies that did not provide quantitative information about exposure, or verify adverse outcome. Further, a meta-analysis of those studies concluded that they did not establish the alleged association (63), and because the studies were inconclusive about outcome and waste gas levels, they could not be used as the basis for setting occupational health standards. Further, the studies that had suggested an association were conducted before scavenging excess gas was a common practice. On the labor ward, excess gas scavenging reduces pollution to recommended limits in the majority of cases (64, 65). Health care workers in labor rooms without scavenging systems are at risk for excessive occupational exposure (66). In the U.S., hospital rooms are well ventilated and Nitronox machines have an active scavenging device.” (Rosen MA. Nitrous oxide for relief of labor pain: A systematic review. Am J Obstet Gynecol 2002;186:S110–126.)



“There is a tremendous abuse potential for N20, and perhaps other countries do not seek to control access, but the US does. Dentists often abuse N2O, resulting in neuropathy. N2O cylinders sitting around would be likely to be abused.”

There is potential for abuse of N2O in hospitals, just as there is potential (and actual) abuse of almost all drugs that are used for pain abatement. But N2O canisters are not just sitting around in those hospitals in which it is used. (FYI, it is used not only in surgery and labor, but in many emergency rooms, and in many women’s health care centers, where it is used during procedures.) Hospitals have to control many substances, including blood, bacterial contamination, radio-active substances, and all pain medication, among others. No US hospital would just let any of those materials “sit around” without control. Nitrous oxide is not, however, the substance which provides the biggest risk of abuse in the US, and to the extent that N2O is abused, there are many sources easier to access than a hospital. Canisters of it have traditionally been thrown from floats during Mardi Gras parades, and somehow or other, teenagers seem to be able to get it for getting happy (it’s called “laughing gas”, after all) during rock concerts. It is also sold in every can of fake whipped cream; push the button and the fake cream gets fluffed up by N2O. Some tattoo parlors also use it. The possibility of abuse is not an acceptable reason to fail to provide a service or product that is needed for serious purposes.

“Nitrous can be administered in a “safe” 50% mixture with O2, but the results can be highly variable and are unpredictable. Some patients get little relief, while the same inhaled concentration could render others unconscious.”

Dr. Rosen described it as “safe for parturient women, their newborns, and health-care workers in attendance during its administration.” He has provided it to women during labor for more than 30 years and has never seen either a woman or a baby be harmed as a result. It is true, however, that the effectiveness of nitrous oxide analgesia is unpredictable. Although about two-thirds of women find it to be effective “enough” and are satisfied, a few women report that it was not helpful. A consumer oriented book co-authored by Dr. William R. Camann, Director of Obstetric Anesthesia at Brigham and Women’s Hospital in Boston and a past president of the Society for Obstetric Anesthesia and Perinatology (Easy Labor: Every Woman’s Guide to Choosing Less Pain and More Joy during Childbirth. New York: Ballantine Books; 2007) noted that “The gas can cause nausea and vomiting in some women” and that “Very rarely, if too much gas is inhaled, it can result in a loss of consciousness.” But that does not happen if the rule of self-administration is followed, as it would be in any setting that provides careful care to women during labor. As Dr. Camann noted, “The mask will not be attached to you while you inhale the gas. This is intentional and will prevent you from inhaling too much gas at once. If you become too drowsy as a result of the gas, you will no longer be able to hold the mask or mouthpiece to your face.” He also noted that there are no known clinical side effects to impact the newborn.


Dr. Camann described the effectiveness as “a kind of strange sensation of feeling the pain while at the same time feeling a sense of bliss. So, the pain may still exist for some women, but the gas may create a feeling of: “Painful contraction? Who cares?!”

“Disinhibition regularly occurs (it was described in the demonstration that gave W.T.G. Morton, one of the founders of surgical anesthesia, the idea) and can lead to dangerous behavior, such as excitation and pulling out IVs. People can have amnesia from N2O; while receiving it they can be screaming in pain, but later not remember.”

Nitous oxide used to be used in much higher concentrations—70 or 80% or even more, compared to just 50% now, so Dr. Morton was responding to something very different from modern day use of a 50/50 standardized ratio of N2O versus oxygen. This anesthesiologist may also be confused between the disinhibition that was associated with “twilight sleep” and other mixtures of drugs including scopolamine, which were still being used when I was a nursing student at the University of Washington in the very early 1960s. Screaming, swearing women were being tied to their beds in disgraceful and humiliating states of disinhibition. I got to know Dr. John Bonica, one of the giants of anesthesia, while I was there. He was a wonderful man. Perhaps he invented obstetric spinals and epidurals in response to the terrible conditions during labor in most American hospitals at that time. But this does not occur with a 50/50 mixture of N2O and oxygen when the rule of self-administration is followed. The anesthesiologist’s statement seems more consistent with the effects of “twilight sleep”, which caused women to have no memories of giving birth.

“The patients and nurses at my hospital would not accept what N2O has to offer.”

With all due respect, I wonder if any one person can really speak for all of the nurses and patients at any hospital, especially if they had access to unbiased information and were able to observe and talk with women using nitrous oxide during labor. Epidurals are very popular and appreciated by many, indeed probably most women giving birth in the US, and I am grateful that most women who want an epidural can have one. But some women don’t want an epidural, and they should be offered a safe and reasonably effective alternative. I doubt that women who give birth in the hospital in which this anesthesiologist practices are offered an alternative. If N2O were offered, I doubt that most women would choose it. But a few would, especially after they learned more about it and after it had been used by a few other women in that community. Nitrous oxide is widely used and appreciated by women in many other countries—including countries in which medical science and care are at least as advanced, if not more so, than in the U.S. Virtually all of these countries have better pregnancy outcomes than we do.

My interest in expanding access to N2O as an analgesic for women during labor in the US is not for the purpose of diminishing use of epidurals. There will always be a big, important place for epidurals during labor. But not every woman wants the same thing, and nitrous oxide has some benefits and characteristics that make it very attractive to some women:

  • Because the laboring woman administers N2O to herself, she has complete control over the frequency and dose used, when it is started, and when it is put away. This gives her a sense of control over herself and over her pain.
  • N2O enters the woman’s body quickly through her lungs. Pain relief begins in one minute or less. If N2O equipment is available in the room—as it is in almost every hospital in the United Kingdom (UK), Sweden, Finland, Australia, Israel, etc., nitrous oxide can be started easily and simply and become effective in a minute. There is no need to call and then wait for an anesthesiologist or nurse anesthetist and set up for and conduct a sterile invasive procedure.
  • It is eliminated just as quickly, also through her lungs. Women who use nitrous oxide during labor can pick it up and put it down—start and stop at will. A woman who needs help during a particularly intense part of labor can start it when she needs it but stop the effect completely in order to experience and participate fully in the act of giving birth. A couple breaths of room air and the effect is gone.
  • The ease and quickness with which N2O can be started is an important benefit when an emergency that requires a painful procedure occurs, such as the need for forceps.
  • Nitrous oxide may make it possible for women who do not want an epidural or narcotics to manage their labor pain so that they can achieve their goal.
  • N2O may help women endure the period between when they ask for and when they receive an epidural.
  • Because N2O doesn’t cause complications that affect the woman’s vital functions, it’s not necessary to use continuous electronic fetal monitoring or start an IV. It doesn’t interfere with her ability to walk or control her bladder; she can get up and walk to the bathroom. Since there’s no tube leading from her back into tissue near her spinal cord, she can take a bath without danger of infection. Hospital maternity units and freestanding birth centers in the UK have portable nitrous oxide equipment that women use while relaxing in a bath.
  • Dr. J. Whitridge Williams, who was one of the leading obstetricians in the US during the early nineteen hundreds, headed the department of obstetrics at Johns Hopkins and wrote the most influential obstetrics text book—Williams’ Obstetrics—praised nitrous oxide because it doesn’t diminish the force of contractions or have any other negative impacts on the physiology of labor.

None of these attributes is true of epidurals. Women often have to wait before an epidural can be started.

Once an epidural has been placed, it is pretty much on board for the duration of the labor. A woman who really only needed help during a specific phase of labor, has to wait for the epidural to “wear off.”

Most women who have had an epidural are not able (or allowed) to get out of bed. They will have to use bedpans, and many of them cannot urinate spontaneously and therefore need to have a catheter placed in their bladder.

Women who have epidurals are at increased risk of a number of complications and therefore need to be monitored more closely than is necessary for women who don’t have epidurals. They can expect to have an IV, not be allowed to eat, have continuous electronic fetal monitoring, et cetera.

Although very rare, some very serious—even disastrous—complications can occur due to trauma, bleeding or infection at the site of an epidural. Deaths are exceedingly rare, but have occurred.

One to three percent of women who have epidurals during labor experience intense post-dural-puncture headaches during the postpartum period. Although these headaches can be effectively treated with another procedure, they occur during a precious period of time during which women want to be able to spend concentrated time breastfeeding and bonding with their newborn.


Epidurals do affect the physiology of labor, decreasing the effectiveness of contractions, relaxing the muscles of the pelvic floor, and—due to lack of sensory feedback to the woman—making it difficult or impossible for the woman to use positioning and purposeful efforts of her voluntary muscles to augment the efforts of her body that are not under her control. In most cases it’s necessary to give a lot of Pitocin, but even then, labor is usually somewhat longer. Relaxation of the muscles of the pelvic floor seem to make it harder for the baby’s head to rotate into the optimal position for birth (Liebermann E, Davidson K, Lee-Parritz A, Shearer E. Changes in fetal position during labor and their association with epidural analgesia. Obstet Gynecol 2005;105-974-82), increasing the proportion of babies who need either a cesarean section or use of forceps or vacuum to achieve a vaginal birth The rate of spontaneous vaginal births is significantly lower for nulliparous women who have an epidural during labor (Lieberman I, O’Donoghue C. Unintended effects of epidural analgesia during labor: A systematic review. Am J Obstet Gynecol 2002;186:S31–68.) The only two alternatives to a spontaneous vaginal birth are an operative vaginal birth or a cesarean delivery. Operative vaginal births are responsible for increased rates of many serious complications for both the mother and the baby, including, for the mother, a high incidence of lacerations that extend from the vagina to the anus or even into the rectum. Either alternative to a spontaneous vaginal birth is something to avoid.

“A properly done labor epidural allows the mother to be fully sentient with well controlled pain and the ability to cooperate.”

Properly administered and monitored use of N2O also allows the mother to be fully sentient. Although the effectiveness of nitrous oxide is variable and less than the effectiveness of epidurals, it is effective enough for about 2/3rds of the women who try it. Some women do not want complete obliteration of their pain. “The experience of labor pain is . . . complex, subjective, multidimensional” and “occurs in the context of an individual woman’s physiology and psychology, and the sociology of the culture surrounding her. That culture . . . includes the beliefs, mores and standards of her family and community.” (Lowe, NK. The nature of labor pain. Am J Obstet Gynecol 2002;186(5):S16–24.)


Women who have been using N2O during labor but have not had an epidural are better able to cooperate if they need to change their position in order to facilitate a maneuver during, for instance, an unanticipated vaginal breech birth.

“N2O has some analgesic properties, but they only come with a clouding of the sensorium and risks such as combativeness, loss of consciousness, and pulmonary aspiration.”

I don’t know where the idea about combativeness comes from. If the rule of self-administration is followed, a woman who was getting too drowsy would stop pushing the button to keep the gas turned on and let her hand fall away from her face before she would lose consciousness. This extreme example might have happened some time in the past, when higher concentrations were used, scavenging wasn’t used, and the rule of self-administration was not adhered to. I won’t bother to give extreme examples of damage and deaths caused by epidurals, except to say that they happen but are rare.

A couple of years ago I exchanged emails with the chief of obstetrics at a well-respected university hospital that stopped offering nitrous oxide to women during labor during the early 1990s. The main people providing nitrous oxide to women during labor at that hospital at that time were midwives. There had been a very high level of patient satisfaction among women who chose this method of analgesia, and the midwives knew of no complications associated with use of nitrous oxide during the years it had been used at this hospital. When this option was withdrawn, some women who had used it during a previous birth and returned to the hospital for their next birth were shocked and disturbed to find out that it was no longer available and made their feelings known. One woman was so angry and adamant that the chief of obstetrics finally let her labor in a cesarean section room, which had piped in nitrous oxide.


When I asked him why he had removed the N2O equipment and banned its further use for women during labor in that hospital, he gave several reasons, including advice from the Obstetric Anesthesia Service, liability concerns from institutional leadership, and “a few scary anecdotal stories”. In fact, however, he had never seen a bad outcome associated with use of nitrous oxide, although he’d heard a story about a woman whose husband strapped the mask to her face and she vomited and aspirated some of the vomit. He didn’t recall the source of the story. I, in contrast, personally knew a midwife who had seen a woman almost die from an epidural. He’d heard a rumor about something bad that might have happened; if so, it was the result of poor practice. Bad things do happen when hospital staff do not provide a high standard of care. In addition, bad things happen as a result of unnecessary cesareans and operative vaginal deliveries even when they are performed correctly, and epidurals result in increased need to use one or the other of those means to achieve delivery.

“If one wants analgesia free of risks of inhaled vapors, one can use injections of demerol, morphine, etc. These make the baby a little sleepier, but not critically so unless used in large and repeated doses.”

I think that this anesthesiologist is unduly worried about occupational risks that have been dealt with and require only proper equipment and diligence, and that he is reacting to protect or create the work environment that he prefers, without consideration for offering any choices to women. Our Bodies Ourselves is and has always been committed to providing women with the fullest, most accurate information possible so as to empower and enable them to make knowledgeable choices.

Most women’s natural inclination is to avoid unnecessary pain, so epidurals are very popular. Epidurals are an excellent method for many women—not only the best method, but truly essential for some. But this is America! Some women, relatively few but some, really don’t want an epidural. They should be offered an alternative that does not depress the newborn’s respirations and can be used right up to and during the actual birth, if that is what the woman wants. Nitrous oxide is a safe, inexpensive, simple to use, reasonably effective labor analgesic that is widely used by women in many other countries but was arbitrarily withdrawn from use in all but two West Coast academic hospitals when anesthesiologists began to offer obstetric epidurals.

Now epidurals are so popular that anesthesiologists and nurse anesthetists are having to really stretch to provide them and cannot provide 24 hour/7-day-a-week coverage for every hospital in the country. This relative shortage is likely to get worse as baby-boomer doctors and nurses retire and the number of babies born in the U.S. continues to rise. The situation is worst in rural areas. The number of births to white women who are not Hispanic is slowly declining, while the number of births to Hispanic women and women of all races other than white are increasing. We all like to eat, and it is important for any civilized country to be able to provide proper maternity care to women who live in the parts of the country that produce our food. Anesthesiologists should be more concerned that all women have access to safe and reasonably effective pain relief during labor instead of disdaining a safe and reasonably effective method of analgesia that they perceive to be less good than the one that they alone can provide.

Epidurals are not only popular among women, they are also popular among many anesthesiologists, obstetricians, family physicians, nurses, and midwives. Taking care of a woman who is experiencing labor without an epidural, even if the edge has been taken off of her pain, is very different from taking care of a woman who may not be in any pain and is chatting calmly or watching TV. Women who have epidurals during labor are at risk for a number of serious complications, have to be monitored more closely than women having normal labor, need a lot of treatments, and may need some kind of emergency response. But for the most part these are technical aspects of care—not the much more intimate and intensive kind of care required by a woman who is much more thoroughly engaged with giving birth. Once doctors and nurses—and even midwives—get used to a quiet labor unit, with all or virtually all of the women on epidurals, the whole ambience of the unit and flow of the work change, and they may not want to work with women who don’t have an epidural.

But there are some serious ethical issues in this scenario. One is the quality of informed consent obtained for epidurals. Few women are told the whole story about the risks. In addition, women in most hospitals are not offered any really viable alternative to an epidural. Having a baby is not like having an appendectomy. In a study in which a researcher asked women in a nursing home to describe the single day that they remember most strongly as a very important and memorable day, most of them remembered the experience of giving birth (Simkin P. Just another day in a woman’s life? Women’s long-term perceptions of their first birth experience. Part I. Birth 1991; 18:203-10). Giving birth is an important event in women’s lives; they deserve some choices. Is it ethical to not even offer another way to help them cope with pain? If a safe, simple, inexpensive, reasonably effective method that is used and appreciated by the majority of women in many other countries is shut out of almost all hospital completely, then women aren’t even offered a choice. And the decisions that result in that lack of choice are driven by factors that have nothing to do with safety.


Is that ethical? And is that what we are willing to accept as the standard for maternity care in the USA?

Our thanks go to Judith for furthering this discussion.

Update: Judith requested that that we make several small corrections; the changes were made on May 16.

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