lunes, 8 de octubre de 2012

Research Activities, October 2012: Comparative Effectiveness: New research examines use of nitrous oxide for labor pain

Research Activities, October 2012: Comparative Effectiveness: New research examines use of nitrous oxide for labor pain

Comparative Effectiveness

New research examines use of nitrous oxide for labor pain

A new research review from the Agency for Healthcare Research and Quality's (AHRQ's) Effective Healthcare Program has evaluated the use of inhaled nitrous oxide, or "laughing gas," to manage maternal pain during labor. Although nitrous oxide is commonly used in many countries for labor pain management, only five centers in the United States are known to provide it as an option. However, nitrous oxide offers several potential benefits that may make it appealing to women in the United States. For example, it is inexpensive, noninvasive, and can be self-administered as needed at any point during labor.
As expected, the research review found that nitrous oxide was less effective at controlling pain than epidural analgesia, but it noted that the quality of available studies was generally poor. The review also examined the effect of nitrous oxide on route of birth (i.e., vaginal, assisted, or cesarean), but the strength of evidence was insufficient to determine the effect. Additional research is needed to assess its effectiveness for pain control, women's satisfaction, type of birth, harms, and health system factors related to the use of nitrous oxide in labor.
Most negative effects to the mother reported in the study were unpleasant side effects, such as nausea, vomiting, dizziness, and drowsiness. The study also looked at the effects on newborns and found that delivery room testing scores in newborns whose mothers used nitrous oxide were similar to those of newborns whose mothers used other labor pain management methods or no pain management treatments.
These findings can be found in the research review, Nitrous Oxide for the Management of Labor Pain. This review adds to AHRQ's growing library of resources on women's health.
To access this review and other materials that explore the effectiveness and risks of treatment options for various conditions, visit the Effective Health Care Program Web site at

Nitrous Oxide for the Management of Labor Pain


On August 1, 2011, two amendments were made to this protocol. To view these amendments, please see the section titled “Summary of Protocol Amendments.”

Table of Contents

Background and Objectives for the Systematic Review

According to data from the Centers for Disease Control and Prevention (CDC), more than 4 million births occur in the United States each year; in 2007, there were 4,316,223 births.1 The 2006 Listening to Mothers II survey found that 86 percent of responding women reported using one or more types of medication for pain relief; 76 percent used epidural or spinal analgesia/anesthesia, 22 percent received narcotics, 3 percent received general anesthesia, and 3 percent used nitrous oxide (likely an overestimate considering how few U.S. facilities offer this method as described later in this section). Although this survey is limited by reliance on women’s self-reporting of analgesia use, it provides a general sense of the relative use of each method in the U.S.2 A 2002 review of labor pain management strategies used in U.S. hospitals—stratified by number of yearly births and size of hospital—found that, among women who gave birth in 1997, from 21 to 50 percent received epidural analgesia, from 5 to 11 percent received combined spinal-epidural analgesia, from 40 to 56 received parenteral analgesia, and from 2 to 13 received paracervical or spinal analgesia.3 In the same study, from 10 to 17 percent of women did not receive any form of analgesia.3
Nitrous oxide is a commonly available option for labor pain relief in several countries outside the U.S. Rosen’s 2002 systematic review on the topic cites evidence that nitrous oxide is used in the United Kingdom by approximately 50 to 75 percent of women and in Finland by approximately 60 percent of women.4 In other studies, Irestedt found that 65 percent of women in Sweden received nitrous oxide for labor pain relief in 1991,5 and a 1995 survey of hospitals in Ontario, Canada, found that nitrous oxide was available for labor pain analgesia in 75% of responding hospitals.6 Nitrous oxide is also commonly used for labor analgesia in Australia and New Zealand.4The widespread use of nitrous oxide in other countries suggests it is an effective labor pain relief method.
Only three centers in the U.S. are known to currently provide nitrous oxide as an option for labor pain relief: the Birth Center at the University of California San Francisco (UCSF) Medical Center, the University of Washington Hospital in Seattle, and St. Joseph Regional Medical Center in Lewiston, Idaho. Bishop has briefly described the UCSF practices in “Administration of Nitrous Oxide in Labor: Expanding the Options for Women,”7 including contraindications, preparation of the patient, and the documentation and competency requirements for midwives. The UCSF model uses a mixture of 50 percent nitrous oxide and 50 percent oxygen that is self-administered by the patient after initial instruction on use and potential side effects. No related publications or descriptions of the option used at the University of Washington Hospital or St. Joseph Regional Medical Center could be located in the literature.
Inhaled self-administered nitrous oxide in a 50/50 mix (e.g., Nitronox) is the most common method of nitrous oxide administration for labor pain relief described in the biomedical literature. Some literature addresses 50 vs. 70 percent concentrations of nitrous oxide in oxygen, and other literature addresses continuous vs. self-administered/intermittent administration. Alternatives/comparators to nitrous oxide include: epidural analgesia/anesthesia; systemic drugs such as opioids administered intravenously, intramuscularly, or orally; other inhalational agents such as sevoflurane and isoflurane; nonpharmacologic methods; and no pain relief.
Literature reporting on the use of nitrous oxide for the management of labor pain is sparse when compared to the use of other forms of analgesia/anesthesia. Initial searches of the PubMed database identified more than 600 studies. After the case reports and the nonoriginal research reports are eliminated, almost 500 studies remain. Currently, the Agency for Healthcare Research and Quality has no completed or in-progress products on the use of nitrous oxide. A search of and the National Institutes of Health RePORTER database of funded research yielded no results, suggesting that nitrous oxide analgesia is not an active research topic.
Most women in the U.S. use some type of medication for labor pain relief. However, the option of using nitrous oxide to relieve labor pain is limited by its lack of availability. With such prevalent use of nitrous oxide during labor in other countries and potential advantages of this pain relief method, such as being less expensive and invasive than widely used regional anesthesia, this review attempts to assess the effectiveness of nitrous oxide in managing labor pain and to identify the potential factors that may influence its availability and use within the U.S. Our key questions have been structured with this goal in mind. The primary outcomes for consideration, as identified by our Technical Expert Panel, include the comparative effectiveness of nitrous oxide for the management of labor pain, the influence of nitrous oxide on the satisfaction with the birth experience, the health system factors influencing its use within the U.S., and any adverse effects associated with this intervention. It is our intention to evaluate the relative effectiveness of nitrous oxide when compared with other pain relief methods, but this comparison is distinct from the assessment of the efficacy of nitrous oxide as a sole pain relief method and may not be adequately reported on in the biomedical literature. With the rate of cesarean birth continuing to rise—31.8 percent of all U.S. births reported in 20071—it is also important to address whether the use of nitrous oxide during labor influences the route of birth in women initially intending a vaginal birth.


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