Elsevier

Journal of Clinical Anesthesia

Volume 40, August 2017, Pages 40-45
Journal of Clinical Anesthesia

Original Contribution
Nitrous oxide for labor analgesia: Utilization and predictors of conversion to neuraxial analgesia

https://doi.org/10.1016/j.jclinane.2017.04.005Get rights and content

Highlights

  • Only a small number of women opted to use nitrous oxide during labor.

  • Nitrous oxide offered limited analgesia to laboring women.

  • The majority of women using nitrous oxide during labor converted to neuraxial analgesia.

  • Labor induction and augmentation were associated with conversion to neuraxial analgesia.

Abstract

Study Objective

We examined the characteristics of women who choose nitrous oxide for labor analgesia and identified factors that predict conversion from nitrous oxide to labor neuraxial analgesia.

Design

Retrospective descriptive study.

Setting

Labor and Delivery Ward.

Patients

146 pregnant women who used nitrous oxide for analgesia during labor and delivery between September 2014 and September 2015.

Interventions

Chart review only.

Measurements

Demographic, obstetric, and intrapartum characteristics of women using nitrous oxide were examined. Multivariable logistic regression was performed to identify factors associated with conversion from nitrous oxide to neuraxial analgesia. Data are presented as n (%), median [IQR], adjusted relative risk (aRR), and 95% confidence intervals (CI) as appropriate.

Results

During the study period, 146 women used nitrous oxide for labor analgesia (accounting for 3% of the total deliveries). The majority (71.9%) of women who used nitrous oxide were nulliparous, and over half (51.9%) had expressed an initial preference for “nonmedical birth.” The conversion rate to neuraxial blockade was 63.2%, compared to a concurrent institutional rate of 85.1% in women who did not use nitrous oxide. Factors associated with conversion from nitrous oxide to neuraxial blockade were labor induction (aRR = 2.0, CI 1.2–3.3) and labor augmentation (aRR = 1.7, CI 1.0–2.9).

Conclusion

Only a small number of women opted to use nitrous oxide during labor, analgesia was minimal, and most converted to neuraxial analgesia. Women with induced and augmented labors should be counseled about the increased likelihood that they will convert to neuraxial analgesia.

Introduction

Nitrous oxide is an anesthetic gas with NMDA antagonistic properties that offers rapid-onset inhaled mild analgesia. The first description of its use during labor and delivery was in 1881 [1], and women throughout the world continue to use it as a labor analgesic today. The minimally invasive delivery method of nitrous oxide offers a modality for managing labor pain that appeals to women who desire labor analgesia without a neuraxial block. This group of women could comprise a significant proportion of obstetric patients, with 26% of women expressing a preference for delivery without neuraxial analgesia in a 2010 national survey performed in France [2]. However, until recently, nitrous oxide was not widely available in the United States [3]. In a nationwide survey performed in the United States in 2000, only a small minority of women (2%) reported using nitrous oxide [4]. Since that time, patient expectations fueled by media coverage have promoted greater nitrous oxide use in the United States. The availability of nitrous oxide for labor analgesia has increased from only five United States institutions in 2012 [3] to several hundred hospitals and birth centers in 2016 [5].

Cultural and societal expectations play a large role in labor preferences [6], [7]. Despite the recent resurgence of nitrous oxide use for labor analgesia in the United States, few studies have examined populations of women that use nitrous oxide for labor analgesia that are applicable to pregnant women in the United States today. The utilization of nitrous oxide for labor analgesia, the rate of conversion from nitrous oxide to neuraxial analgesia for labor, and predictors of which patients are most likely to convert to neuraxial analgesia are unknown. This information can assist anesthesia providers in the United States who are interested in offering a new nitrous oxide service for labor analgesia to help determine expected demand and utilization. It will also help anesthesiologists to tailor their labor analgesia counseling and consent to individual patients who are more likely to convert to neuraxial analgesia.

The primary aim of this study was to determine the utilization and characteristics of women who choose to use nitrous oxide for labor analgesia. The secondary objective was to evaluate factors that predict the conversion to neuraxial analgesia.

Section snippets

Materials and methods

After obtaining Stanford University IRB approval, we reviewed electronic medical records of women who used nitrous oxide for labor analgesia over 13 months (September 2014 to September 2015). The study was conducted at Lucile Packard Children's Hospital, a tertiary obstetric center with approximately 4500 deliveries per year and a labor epidural rate of over 80%.

There is dedicated, “around-the-clock” anesthesia coverage for the obstetric patients, with anesthesia care provided by an anesthesia

Results

We abstracted data from 146 records of women who used nitrous oxide. During the study period 4698 women delivered at our institution, therefore women who used nitrous oxide accounted for 3.1% of all deliveries. Demographic and obstetric characteristics of these women are outlined in Table 1. Women who used nitrous oxide were primarily English-speaking (82.1%), and nulliparous (71.9%). More than half (51.9%) had initially indicated a preference for “nonmedical birth” according to their birth

Discussion

Only a small proportion (3%) of women at our institution chose to use nitrous oxide. This stands in stark contrast to reports outside the United States showing over 50% to nearly 80% utilization of nitrous oxide in Australia and the United Kingdom, respectively [9], [10]. The reasons for this large disparity in use of nitrous oxide for labor analgesia are not well established. The Agency for Healthcare Research and Quality identified many potential factors influencing the use of nitrous oxide

Disclosures

None.

Acknowledgements

This paper has been presented at the 2016 Society of Obstetric Anesthesiology and Perinatology Annual Meeting in Boston, Massachussetts and at the 2016 American Society of Anesthesiology Annual Meeting in Chicago, Illinois.

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    1

    Present address: Department of Pediatric Anesthesiology, Perioperative, and Pain Medicine, Texas Children's Hospital, Baylor College of Medicine, 6621 Fannin Street, Houston, Texas 77030, USA.

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