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Utilization and Predictors of Efficacy of Nitrous Oxide for Labor Analgesia
Abstract Number: T-25
Abstract Type: Original Research
Introduction: Nitrous oxide (N2O), a widely used labor analgesia outside the United States, has recently gained popularity in the United States.(1,2) We examined the characteristics of women who choose N2O for labor pain management, efficacy of analgesia, and factors that predicted conversion to labor epidural analgesia.
Methods: After IRB approval, we reviewed the medical records of all women who used N2O between September 2014 and September 2015 after it was introduced at a US tertiary obstetric center. We collected maternal demographic and obstetric data, analgesic endpoints, and neonatal outcomes. Bivariate correlations of maternal characteristics and labor epidural use were determined. Multivariate logistic regression was performed to determine factors that predicted conversion to labor epidural among women who used N2O. Data is presented as n (%), median [IQR], adjusted relative risk (aRR), and 95% confidence intervals (CI) as appropriate.
Results: 148 (3.2%) of the 4698 women who delivered vaginally within the study period received N2O. The characteristics of these women are outlined in Table 1. The median duration of use was 80 min [38-143]. Median verbal pain score immediately prior to N2O initiation was 8 [6-9], and median pain score change after N2O use was 0 [-2 to 1]. Labor epidural analgesia was used by 60% of women using N2O, which is significantly different than the 74% institutional epidural rate (p=0.0001). Bivariate analysis for association with conversion to neuraxial analgesia revealed several candidate variables: language (p=0.17), nulliparity (p=0.005), labor type (p<0.0005), birth plan (p=0.03), pain score prior to nitrous oxide (p=0.0005), and cervical dilation (p<0.00005). In the multivariate model, compared to spontaneous labor, labor induction (aRR=2.0, CI 1.2-3.3) and augmentation (aRR=1.7, CI 1.0-2.9) were associated with epidural use.
Conclusion: Our findings suggest that only a small proportion of women chose to use N2O, analgesia was modest, and duration of use was limited. Although the majority converted to neuraxial analgesia, the epidural rate was lower than women who did not use N2O. Labor induction and augmentation predicted epidural use. Future studies are needed to further delineate laboring women who most benefit from N2O.
1. Anesth Analg 2014;118:153-67.
2. Am J Obstet Gynecol 2002;186:S110-26.