Evaluation of Maternal and Fetal Outcomes Following Nitrous Oxide and Neuraxial Labor Analgesia

The use of nitrous oxide during labor is common in several countries including the United Kingdom, Finland, Canada, Australia and New Zealand.1, 2 The use of nitrous oxide during labor has undergone a resurgence in popularity recently in the United States and became available at Brigham and Women's hospital in August 2014.

Inhaled nitrous oxide has a rapid onset (30-50 seconds) and clearance with a half-life of about 5 minutes.3 It can be used for analgesia during the first, second and third stages of labor, as well as during post-delivery procedures such as laceration repair, manual removal of the placenta, and uterine curettage. It is also commonly used to facilitate the initiation of epidural analgesia.4 At the Brigham and Women's Hospital, a pneumatically driven gas mixer is designed to deliver a 50% oxygen and 50% nitrous oxide mixture to patients. Nitrous oxide passes readily across the placenta, and reaches equilibrium within a few minutes; the fetal maternal concentration ratio after 2 minutes of inhalation is 0.64.5 Hence, when administered at 50% concentration to the mother, the fetal concentration approximates at 32%.

Despite its long track record of maternal safety reported in numerous countries, the effect of nitrous oxide on the fetus is less well-studied. A number of studies have published data on the use of nitrous oxide for labor analgesia, including the effectiveness in labor analgesia, maternal satisfaction and maternal fetal adverse effects. Most of these studies have not identified adverse neonatal outcomes. However, these studies used Apgar scores or neonatal behavior scores as outcome measures and the quality of these studies was predominately poor.

The purpose of this study is to evaluate maternal and neonatal outcomes in parturients who used nitrous oxide and neuraxial labor analgesia during labor.