Nitrous Oxide Use for Pain in Labor, Conversion to Neuraxial Analgesia, and Birth Outcome.

A variety of labor pain management options is essential to patients and their care providers. Inhaled, patient controlled nitrous oxide (N2O) is a valuable addition to these options. The purpose of this study was to examine laboring patient, newborn, and provider characteristics associated with N2O use for pain relief in labor and to examine the association between N2O, conversion to neuraxial analgesia, and cesarean birth. This was a retrospective observational cohort study of the first year of N2O use in one large academic medical center. Patients at least 37 weeks' gestation who were admitted for labor with intended vaginal birth from August 1, 2018, to June 30, 2019, were included (N = 2605). Laboring patient and newborn factors and their relationship to N2O use were calculated as unadjusted and adjusted relative risks (RRs). Poisson regression was used to model the association between N2O use and subsequent use of neuraxial analgesia and type of birth for both nulliparous and multiparous patients. Overall, 20.2% of patients used N2O during labor. Multiparous patients were 24% less likely to use N2O than nulliparous patients (RR, 0.76; 95% CI, 0.69-0.84). Use of N2O did not differ significantly between patients cared for by midwives compared with patients cared for by physicians (RR, 0.95; 95% CI, 0.90-1.00). In multivariable modeling, N2O use in multiparous patients was associated with a 17% decrease in use of neuraxial analgesia (RR, 0.83; 95% CI, 0.73-0.94). There was no association between N2O use and use of neuraxial analgesia in nulliparous patients (RR, 0.99; 95% CI, 0.93-1.06). N2O use was not associated with cesarean birth in either group. N2O is an important pain management option for laboring patients and those who care for them. Study results may assist midwives, physicians, and nurses in counseling patients about analgesia options.

DeJoy S ，Killeen C ，Jackson-Köhlin D ，Psaltis A ，Knee A ... -  《-》

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

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 (N2 O) analgesia and to determine predictors of conversion from N2 O to neuraxial analgesia. This was a prospective chart review study. Individuals aged at least 18 years who used inhaled N2 O 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-N2 O cervical dilatation, and post-N2 O cervical dilatation on the odds of conversion from N2 O to neuraxial analgesia. In this cohort, 31% who chose N2 O for analgesia did not convert to any other analgesic method. Significant positive predictors for conversion from N2 O 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-N2 O cervical dilatation (OR, 0.8; 95% CI, 0.7-0.9) were negative predictors. Adverse effects related to N2 O use during labor were rare (8%) and were not a significant reason for conversion to neuraxial analgesia. Parturients had moderately high satisfaction with N2 O 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. Understanding predictors of conversion from inhaled N2 O to neuraxial analgesia may assist perinatal care providers in their discussions with women about analgesia options during labor. N2 O is a useful, safe option for labor analgesia in the United States.

Nodine PM ，Collins MR ，Wood CL ，Anderson JL ，Orlando BS ，McNair BK ，Mayer DC ，Stein DJ ... -  《-》

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

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. Retrospective descriptive study. Labor and Delivery Ward. 146 pregnant women who used nitrous oxide for analgesia during labor and delivery between September 2014 and September 2015. Chart review only. 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. 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). 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.

Sutton CD ，Butwick AJ ，Riley ET ，Carvalho B ... -  《-》

Does nitrous oxide labor analgesia influence the pattern of neuraxial analgesia usage? An impact study at an academic medical center.

To compare the rate of epidural use before and after the implementation of nitrous oxide (N2O). Data were obtained from a nursing database of N2O usage and our obstetric anesthesia database. We compared 8 months before and 8 months after the introduction of N2O. It was available 24 h/d, 7 d/wk, consistent with neuraxial analgesia availability. Epidural utilization before and after introduction of N2O was compared using χ2 analysis. Labor and delivery floor. Total number of births over the study period was 8539: 4315 pre-N2O and 4224 post-N2O. The rate of epidural usage was 77% pre-N2O and 74% after N2O (P= not significant, χ2). A total of 762 patients used N2O. Monthly analysis showed no change in pattern of neuraxial analgesia use in post-N2O period compared with the pre-N2O period. The introduction of N2O for labor analgesia was not associated with any change in our rate of labor epidural utilization. Under the conditions of our study, these results suggest that N2O does not discourage neuraxial use for labor pain relief.

Bobb LE ，Farber MK ，McGovern C ，Camann W ... -  《-》

Multicenter Study Evaluating Nitrous Oxide Use for Labor Analgesia at High- and Low-Altitude Institutions.

Nitrous oxide (N2O) has been used nationally as an analgesic in many clinical settings. While neuraxial analgesia is still the most commonly used labor analgesic in the United States, there is increasing use of N2O in labor. Given the reduction in the partial pressure of gases at a higher altitude, N2O has been reported to have reduced analgesic properties. However, there is no study to date evaluating the impact of altitude on labor analgesia and N2O. We conducted a multicenter retrospective data analysis of a N2O registry collected from 4 institutions over a 3-year period. We compared the impact of altitude on 50% N2O administration for labor analgesia, conversion rates to another analgesic modality, as well as collected side effect frequencies and conversion predictors. Multivariable regression models were used to compare clinical characteristics and outcomes between parturients at high and low altitudes, while adjusting for race, ethnicity, education, and age (logistic and linear regressions for categorical and quantitative outcomes, respectively). A total of 1856 laboring parturients (age 18-50) were included in the analysis. The odds of converting from 50% N2O to another analgesic modality had no statistically significant difference between high- versus low-altitude institutions (adjusted odds ratio [aOR], 1.13; 95% confidence interval [CI], 0.90-1.42; P = .3). Yet, when parturients at low altitude converted from N2O, they were more likely (aOR, 3.03; 95% CI, 1.59-5.88) to choose neuraxial analgesia instead of another analgesic modality when compared to high-altitude parturients. This is possibly due to higher epidural rates at the low-altitude institutions. When parturients at high altitude did convert into another modality, they were more likely (aOR, 2.19; 95% CI, 1.14-4.21) to convert due to inadequate pain relief compared to low-altitude parturients; however, missing data may have affected this finding. Laboring individuals at low altitude were significantly more likely to experience side effects (aOR, 2.13; 95% CI, 1.45-3.12). Those requiring labor augmentation, assisted vaginal, or cesarean delivery converted to neuraxial analgesia significantly more often than those that delivered via spontaneous vaginal delivery (P < .05) in both high- and low-altitude groups. This is the first study evaluating 50% N2O as a labor analgesic at high altitude. As expected, we found lower side effects at high altitude, likely due to the lower partial pressure of N2O. However, there was not a statistically significant increase in conversion from N2O to another analgesic modality at high altitude and no clinically significant differences in neonatal outcomes.

Wood C ，Arbet J ，Amura CR ，Nodine P ，Collins MR ，Orlando BS ，Mayer DC ，Stein D ，Anderson J ... -  《-》