By Rebecca H. Allen, MD, MPH, Editor
Associate Professor, Department of Obstetrics and Gynecology, Warren Alpert Medical School of Brown University, Women and Infants Hospital, Providence, RI
In this prospective cohort study at one large academic medical center in Colorado, 31% of women who opted for nitrous oxide for analgesia during labor did not require any other source of analgesia, such as an epidural or intravenous opioids. Risk factors for conversion to other modalities included labor induction, oxytocin augmentation, and labor after cesarean.
Nodine PM, Collins MR, Wood CL, et al. Nitrous oxide use during labor: Satisfaction, adverse effects, and predictors of conversion to neuraxial analgesia. J Midwifery Womens Health 2020; May 26. doi: 10.1111/jmwh.13124. [Online ahead of print].
This prospective cohort study was conducted at a large, urban, tertiary care academic medical center in Colorado between March 2016 and July 2017. Adult women were enrolled in the study during the first or second stage of labor if they opted for nitrous oxide for pain management and were at term (37 to 42 weeks’ gestation).
All women presenting in labor were counseled about the option to receive epidural analgesia, intravenous opioids, or nitrous oxide. Exclusion criteria included women with planned cesarean deliveries. Multiple data variables were collected, including demographic information, medical history, obstetric history, intrapartum course, and specifics of nitrous oxide use. Maternal adverse effects and satisfaction levels also were recorded.
A total of 463 women were enrolled and had complete data for analysis. The majority of participants were nulliparous (60.9%), and the average age was 27.3 years (standard deviation [SD] = 6.3). One hundred eighty-six women (40%) were admitted for labor induction and 101 (22%) underwent oxytocin augmentation of labor. Overall, of the women who used nitrous oxide as their initial pain relief modality, 144 (31%) used it during the entire course of labor. The remainder converted to another option. The mean time of using nitrous oxide was 178 minutes (SD = 213) and the mean satisfaction score on a scale of 0 to 10 was 7.4 (SD = 2.9). The most common adverse effects reported during use were nausea (3.7%) and dizziness (1.7%). There were no reports of excessive sedation. The mode of delivery among the sample was 81% spontaneous vaginal, 0.9% vacuum, 4.5% forceps, and 13.6% cesarean.
Of the 319 women who converted to another method of pain relief, the most common reason cited was inadequate pain relief (96%), followed by a minority for adverse effects (1.6%). Most who converted to another method chose epidural anesthesia (91%). In multivariable analysis, higher odds of converting to another pain control method were found with labor induction (adjusted odds ratio [aOR], 2.9; 95% confidence interval [CI], 1.7-4.9), oxytocin augmentation (aOR, 3.1; 95% CI, 1.6-6.0), and labor after cesarean (aOR, 6.4; 95% CI, 2.5-16.5). Multiparity was protective and decreased the odds of analgesia method conversion (aOR, 0.4; 95% CI, 0.2-0.6).
COMMENTARY
Epidural analgesia is the most common pain control method employed during labor and delivery in the United States. In the past, other options included only intravenous opioids, which are limited in utility because of adverse maternal and fetal effects. However, nitrous oxide recently has become available as another option on many labor and delivery units. The advantages of nitrous oxide (50% N2O and 50% O2) include rapid onset and offset, no need for additional monitoring because of the minimal effects on the maternal cardiovascular and respiratory system, and control by the patient.1 Although it is not considered as effective as epidural analgesia in terms of pain scores, patients may prefer it as an alternative.
Although nitrous oxide has been used for labor pain in other countries for many years, it is relatively new to the United States. The authors of this study wanted to explore the use of nitrous oxide at their institution in Colorado and found a 69% conversion rate from nitrous oxide to another form of pain control. Two other studies from the United States found conversion rates ranging from 40% to 63%, which correspond with the findings from the Nodine et al study.2,3 The finding that oxytocin augmentation and labor induction increased conversion rates is not surprising to me, given that these factors likely are associated with longer labors. Similarly, multiparous women likely do better with nitrous oxide alone, since their labors typically are faster, and they may have a higher tolerance for labor pain because of their past experience.
This study also found a higher rate of conversion among women with a previous cesarean delivery, which the authors suspected may be related to increased anxiety and fear of labor or a slower labor progress. The mean time of nitrous oxide use was 178 minutes in this study, with a wide range reported (five to 1,508 minutes). The authors thought that better education and communication regarding the expected effect for patients who start using nitrous oxide would be beneficial in prolonging use times.
Overall, women were satisfied with nitrous oxide use in this study, even though the pain control was not optimal for the majority. Nevertheless, the method may be satisfactory for other reasons, including the ability to ambulate and the control that the patient has over its use. Even if the patient does not use nitrous oxide for the entire labor, it may be a helpful adjunct and may increase satisfaction with the overall delivery experience. Most patients prefer to have multiple options available for pain control.
During the COVID-19 pandemic, our hospital suspended use of nitrous oxide for labor pain because of the concern for aerosolizing the virus if the patient was infected. It is hoped that nitrous oxide will be reinstated for patient use at some point.
REFERENCES
- American College of Obstetricians and Gynecologists’ Committee on Practice Bulletins–Obstetrics. ACOG Practice Bulletin No. 209: Obstetric Analgesia and Anesthesia. Obstet Gynecol 2019;133:e208-e225.
- Richardson MG, Lopez BM, Baysinger CL. Should nitrous oxide be used for laboring patients? Anesthesiol Clin 2017;35:125-143.
- Sutton CD, Butwick AJ, Riley ET, Carvalho B. Nitrous oxide for labor analgesia: Utilization and predictors of conversion to neuraxial anesthesia. J Clin Anesth 2017;40:40-45.
