Nitrous Oxide for Labor: Choose Wisely

Nitrous oxide has been used for over 100 years to manage pain during medical procedures,it is common to use nitrous oxide as an option in laboring women, in order to help them cope with pain. But although nitrous oxide was once available for labor in the United States, its popularity diminished in the 1970s with the advent of the epidural.

Now nitrous oxide is being incorporated more and more for pain management during labor in the U.S. Possibly fueled by the reintroduction in the U.S. of new nitrous oxide equipment for delivery room use in 2011, it is estimated many hospitals and birthing centers in the U.S. currently offer or will soon offer nitrous oxide for labor.

It is important for women to be informed about their options, and to understand how to have more control over their labor experience. There is much debate over the pros and cons of using nitrous oxide during labor, and so both doctors and patients should be informed on the issue in order to choose wisely.

Nitrous oxide is an inhaled anesthetic gas that works by antagonizing the NMDA receptor, which helps to control other neural pathways. As a pain management aid, it can be used during the first, second, and third stages of labor, as well as during post-delivery procedures.

Nitrous offers temporary pain relief – it does take a couple minutes to reach a therapeutic level, and wears off over a few minutes, which is why it is widely used for certain dental procedures.

(Note: Many people may confuse nitrous oxide used in labor with the use of nitrous oxide in dental practices, but there is a distinct difference. Because the use of nitrous inhalation of gas is controlled by the patient in a labor setting, the concentration of 50% nitrous and 50% oxygen cannot be altered. Dental practices generally utilize variable rates and concentrations of N2O delivery, as it is not patient-controlled).

Nitrous oxide is a ‘greenhouse gas’ and has been estimated to be 300 times as potent as carbon dioxide over a 100-year period.

Nitrous oxide for labor may be administered via a handheld mask that the patient can inhale when she wants to, giving women control over how much and how frequently to breathe the gas as they experience labor contractions.

Studies have shown that nitrous may not reduce pain scores significantly, but it does create a woozy state of mind where patients focus less on the pain they are experiencing.

Many women who choose nitrous like the feeling of being in control; patient satisfaction scores among women who choose nitrous are similar to women who opt for full pain relief with an epidural, in spite of significantly different pain scores.

However, even though its pain management benefits are more subtle, nitrous still has side effects to be considered. Nitrous oxide can make some patients feel nauseous or dizzy, and some women report residual dizziness and drowsiness even hours after labor.

Like some other anesthetic agents, it can cross the placenta. Multiple animal models have shown nitrous to produce adverse effects on the in utero/newborn rapidly developing brain, including widespread brain cell death, deficits in the function of parts of the brain (e.g. hippocampus) and persistent memory and learning impairments.

Despite its current use in several countries, high quality studies of the effects of nitrous oxide on both mother and baby need to be performed in order to offer further clarification on its merits, as suggested by the Agency for Healthcare Research and Quality (AHRQ, 2012).

Data in animals and humans suggest theoretical potential risks to both the mother and baby. Nitrous oxide not only works to provide anesthetic effects at the NMDA receptor, but also inactivates Vitamin B12, a required cofactor for an important enzyme, methionine synthetase.

Decreased methionine synthetase enzyme activity results in increased homocysteine blood levels, which has been associated with changes in how blood vessels react, increased stickiness of blood (e.g. forming clots) and long-term elevation can lead to atherosclerosis in adults.

As well, newer technology has demonstrated signs of DNA changes in animals and even humans with nitrous oxide exposures. Multiple animal models have shown an increased sensitivity to anesthetics in the rapidly developing brain as well as the aged brain. Animal studies have even shown a long-term effect on learning.

While transient nitrous exposure is unlikely to cause harm in humans, more high quality studies in animals and humans are needed to answer the long-term safety and developmental effects of nitrous exposures in mom and babies.

There is also a risk of indirect environmental exposure with inhaled anesthesia. At University of California San Francisco Medical Center, labor and delivery staff have worn badges to measure levels of N2O, to ensure no excess of occupational exposure limits.

The FDA requires the use of a blender device with a scavenger system, to limit occupational exposure. Older studies in the pre-scavenging setting showed increases in infertility and spontaneous abortions among dental workers.

Currently, we lack a body of evidence about the long-term effects on health of workers exposed to low levels of nitrous; this is an area that clearly needs more examination.

Many women who choose to use nitrous often go on to request further pain relief from a labor epidural. Epidural analgesic techniques have evolved to be ‘lighter’ and tailored more to the individual woman during labor. Instead of a “one size fits all” approach, the concentrations and choice of medication can now be applied to meet a woman’s desired level of relief – complete or partial.

Epidurals now can be applied with minimal heaviness of the legs, and still enable women to push at the appropriate time. I began using the ‘walking epidural’ in my hospitals in 1994 and women have been walking during labor with an epidural ever since.

Although the use of nitrous oxide in labor is supported the American College of Nurse Midwives, the American Congress of Obstetricians and Gynecologists (ACOG) has not yet taken a position on nitrous oxide for labor analgesia.

The American Society of Anesthesiologists statement on nitrous oxide for labor includes the need for informed consent and reflects the possibility of long-term adverse effects on child neurologic development.

So the jury is still out on its safety and efficacy – suggesting that we, as modern clinicians, should choose wisely. As we consider additional options for pain management, we must remain cognizant of striking a careful balance between empowering pain control for laboring women, and safeguarding her health and the health of her child.