Nitrous Oxide Use During Labor: Satisfaction, Adverse Effects, and Predictors of Conversion to Neuraxial Analgesia

Introduction: Women desire safe and effective choices for pain management during labor. Currently, neuraxial and opioid analgesia are the most common methods used in the United States. The purpose of this study was to investigate demographic characteristics, safety, and satisfaction in a cohort of parturients who used inhaled nitrous oxide (N₂O) analgesia and to determine predictors of conversion from N₂O to neuraxial analgesia. Methods: This was a prospective chart review study. Individuals aged at least 18 years who used inhaled N₂O during the first or second stage of labor between March 1, 2016, and July 23, 2017, on the labor and delivery unit of one academic medical center (N = 463) and their neonates were included. Data describing maternal and neonatal factors are reported. Logistic regression and chi-square tests were used to model the effects of oxytocin augmentation, labor induction, parity, prior cesarean birth, pre-N₂O cervical dilatation, and post-N₂O cervical dilatation on the odds of conversion from N₂O to neuraxial analgesia. Results: In this cohort, 31% who chose N₂O for analgesia did not convert to any other analgesic method. Significant positive predictors for conversion from N₂O to neuraxial analgesia included labor induction (odds ratio [OR], 2.9; 95% CI, 1.7-5.0), oxytocin augmentation (OR, 3.1; 95% CI, 1.6-6.0), and labor after cesarean (OR, 6.4; 95% CI, 2.5-16.5). Multiparity (OR, 0.4; 95% CI, 0.2-0.6) and post-N₂O cervical dilatation (OR, 0.8; 95% CI, 0.7-0.9) were negative predictors. Adverse effects related to N₂O use during labor were rare (8%) and were not a significant reason for conversion to neuraxial analgesia. Parturients had moderately high satisfaction with N₂O for pain management (11-point scale, mean [SD], 7.4 [2.9]). Five-minute Apgar scores were 7 or greater in 97.8% of the newborns. Discussion: Understanding predictors of conversion from inhaled N₂O to neuraxial analgesia may assist perinatal care providers in their discussions with women about analgesia options during labor. N₂O is a useful, safe option for labor analgesia in the United States.