Safety and risks of nitrous oxide labor analgesia: a review.

INTRODUCTION: This review of the safety and risks of nitrous oxide (N(2) O) labor analgesia presents results of a search for evidence of its effects on labor, the mother, the fetus, the neonate, breastfeeding, and maternal-infant bonding. Concerns about apoptotic damage to the brains of immature mammals exposed to high doses of N(2) O during late gestation, possible cardiovascular risks from hyperhomocysteinemia caused by N(2) O, a hypothesis that children exposed to N(2) O during birth are more likely to become addicted to amphetamine drugs as adults, and possible occupational risks for those who provide care to women using N(2) O/O(2) labor analgesia are discussed in detail. METHODS: Research relevant to the 4 special concerns and to the effects of N(2) O analgesia on labor and the mother-child dyad were examined in depth. Three recent reviews of the biologic, toxicologic, anesthetic, analgesic, and anxiolytic effects of N(2) O; 3 reviews of the safety of 50% N(2) O/oxygen (O(2) ) in providing analgesia in a variety of health care settings; and a 2002 systematic review of N(2) O/O(2) labor analgesia were used. RESULTS: Nitrous oxide analgesia is safe for mothers, neonates, and those who care for women during childbirth if the N(2) O is delivered as a 50% blend with O(2) , is self-administered, and good occupational hygiene is practiced. Because of the strong correlation between dose and harm from exposure to N(2) O, concerns based on effects of long exposure to high anesthetic-level doses of N(2) O have only tenuous, hypothetical pertinence to the safety of N(2) O/O(2) labor analgesia. DISCUSSION: Nitrous oxide labor analgesia is safe for the mother, fetus, and neonate and can be made safe for caregivers. It is simple to administer, does not interfere with the release and function of endogenous oxytocin, and has no adverse effects on the normal physiology and progress of labor.