Inhaled nitrous oxide has been used for labor analgesia since the late 1800s. It is not a potent labor analgesic, but it can provide effective pain relief and is safe for pregnant women, their newborns, and health care workers. Nitrous oxide is useful because of its ease of administration and minimal to no adverse effects on the physiology and progress of labor. Several countries including the United Kingdom, Canada, Australia, Finland, and Sweden use inhaled nitrous oxide, and in the United States there is a growing awareness in recent years of the benefits for labor analgesia.
Nitrous oxide provides analgesia, reduces the patient’s perception of pain, and has an anxiolytic effect, which can be particularly helpful in women who are restless or have difficulty coping during the early stages of labor. It is inexpensive, noninvasive, and readily available, with rapid onset and offset. Compared to epidural analgesia, the effects are not prolonged, mobility is preserved, monitoring needs are less stringent, and a urinary catheter is not necessary.
Nitrous oxide is commonly mixed 50/50 with air and can be self-administered via facemask intermittently about 30 seconds before each contraction. The mask may have a demand valve which opens only during inhalation. These are safety precautions, and as a result, a woman can control the amount she needs and can always decide if she wants to stop and switch to another mode of analgesia, such as an epidural. Effectiveness studies can be challenging due to patients’ opinions about pain changing as labor progresses and the fact that nitrous oxide is not intended to provide complete pain relief.
Side effects of nitrous oxide can include nausea, vomiting, dizziness, and sedation. Although there is risk of occupational exposure to nitrous oxide, this can be significantly reduced with ventilation and proper equipment. Nitrous oxide is transmitted via the placenta, and once the neonate is born and can breathe, the nitrous oxide is rapidly eliminated. There is no increase in the need for neonatal resuscitation, and there are no differences in Apgar scores in neonates in mothers who used nitrous oxide versus other labor analgesia methods or no analgesia at all.
In recent years, there is growing interest in using nitrous oxide for labor analgesia in the United States. While nitrous oxide may not be the most effective method of pain relief for every patient, it is considered a safe and inexpensive way to treat pain during labor.