Across the United States, nitrous oxide (N2O) is attracting attention as a desired option for analgesia during childbirth. Worldwide it remains one of the most common labor analgesics, utilized widely in many countries in Europe (up to 75% of women in the UK), the Middle East, Asia, and Australia1. In the United States, nitrous oxide was commonly used during labor from the 1930s to the 1950s, often given with other potent agents, such as scopolamine, ketamine, or narcotics. It remains in frequent use today for outpatient pediatric dentistry.
In the 1970s, nitrous oxide use in childbirth declined with the increasing availability of epidural analgesia. Many hospitals in the United States no longer installed nitrous oxide gas lines in labor and delivery rooms, and the next generation of American obstetricians, anesthesiologists, and parturients became unfamiliar with its use in labor. Not until consumers and the midwifery community began seeking its use did nitrous oxide begin to re-emerge.2 The US Food and Drug Administration’s (FDA) approval of a portable nitrous oxide delivery system in 2012 further facilitated its re-emergence in this country. New protocols have developed via coordinated team efforts among obstetricians, midwives, nurses, and anesthetists. Today, dozens of hospitals and birth centers in the United States are offering nitrous oxide once again for pain management during labor. Interest in its use is accelerating for those parturients desiring low-intervention births. Centers are increasingly offering such services, as they aim to meet consumer needs and increase patient satisfaction.
Physiology and pharmacology
Nitrous oxide is a colorless, non-flammable, sweet-smelling gas with both anesthetic and analgesic properties when inhaled. Its analgesic and anxiolytic mechanisms of action include inhibition of N-methyl-D-aspartate (NMDA) antagonism, modulation of γ-aminobutyric acid (GABA) nerve pathways and glycine potentiation.3 Along with these effects, increases in dopamine, norepinephrine, and endogenous opioid release decrease pain perception, producing a sense of euphoria and sometimes psychedelic effects.
For labor-related analgesia, women inhale nitrous oxide just prior to the start of and throughout each contraction. Due to low solubility of the gas, there is rapid uptake within 3 to 4 breaths with maximum analgesic effect in 40 to 60 seconds. Following a contraction, there is rapid maternal clearance with cessation of nitrous oxide inhalation. Women remain alert, maintaining motor and sensory function, including a strong laryngeal reflex that helps to prevent aspiration. Intake is self-administered and self-regulated; if the patient becomes too drowsy, she will not be able to hold her mask in place, and the gas will rapidly clear within a few breaths.4
Importantly, the FDA-approved portable nitrous oxide delivery systems for childbirth have safety features that limit gas concentration to a 50/50 mixture with oxygen. Demand valves permit nitrous oxide flow only when the patient establishes a good seal with the mask and engages in purposeful inspiration. In addition, these units are connected to scavenging systems to remove exhaled gas.
The authors report no potential conflicts of interest with regard to this article.
- Rooks JP. Nitrous oxide for pain in labor - Why not in the United States? Birth. 2007;34(1):3-5..
- American College of Nurse-Midwives. Position Statement: Nitrous Oxide for Labor Analgesia. 2011:1-5.
- Emmanouil DE, Quock RM. “Advances in Understanding the Actions of Nitrous Oxide.” Anesthesia Progress. 54.1 (2007): 9–18. PMC. Web. 15 Jan. 2018.
- Rosen MA. Nitrous oxide for relief of labor pain: a systematic review. Am J Obstet Gynecol. 2002;186(5 Suppl Nature):S110-S126.
- Klomp T, van Poppel M, Jones L, Lazet J, Di Nisio M, Lagro-Janssen ALM. Inhaled analgesia for pain management in labour. Cochrane database Syst Rev. 2012;(9):CD009351.
- Likis FE, Andrews JC, Collins MR, et al. Nitrous oxide for the management of labor pain: A systematic review. Anesth Analg. 2014;118(1):153-167.
- Waldenstrom U, Irestedt L. Obstetric pain relief and its association with remembrance of labor pain at two months and one year after birth. J Psychosom Obstet Gynaecol. 2006;27(3):147-156.
- Leong EW, Sivanesaratnam V, Oh LL, Chan YK. Epidural analgesia in primigravidae in spontaneous labour at term: a prospective study. J Obstet Gynaecol Res. 2000;26(4):271-275.
- Paech MJ. The King Edward Memorial Hospital 1,000 mother survey of methods of pain relief in labour. Anaesth Intensive Care. 1991;19(3):393-399.
- Bricker L, Lavender T. Parenteral opioids for labor pain relief: A systematic review. Am J Obstet Gynecol. 2002;186(5 SUPPL.):94-109.
- Su F, Wei X, Chen X, Hu Z, Xu H. [Clinical study on efficacy and safety of labor analgesia with inhalation of nitrous oxide in oxygen]. Zhonghua Fu Chan Ke Za Zhi. 2002;37(10):584-587.
- Harrison RF, Cullen R. A comparative study of the behaviour of the neonate following various forms of maternal intrapartum analgesia and anaesthesia. Ir J Med Sci. 1986;155(1):12-18.
- Zack M, Adami H-O, Ericson A. Maternal and Perinatal Risk Factors for Childhood Leukemia. Cancer Res. 1991;51(14):3696-3701.
- Rooks JP. Safety and risks of nitrous oxide labor analgesia: a review. J Midwifery Womens Health. 2011;56(6):557-565.
- Westberg H, Egelrud L, Ohlson CG, Hygerth M, Lundholm C. Exposure to nitrous oxide in delivery suites at six Swedish hospitals. Int Arch Occup Environ Health. 2008;81(7):829-836.
- Rowland ASAS. Reduced fertility among women employed as dental assistants exposed to high levels of nitrous oxide. N Engl J Med. 1992;327(14):993-997.