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

INTRODUCTION: A variety of labor pain management options is essential to patients and their care providers. Inhaled, patient controlled nitrous oxide (N2 O) is a valuable addition to these options. The purpose of this study was to examine laboring patient, newborn, and provider characteristics associated with N2 O use for pain relief in labor and to examine the association between N2 O, conversion to neuraxial analgesia, and cesarean birth.

METHODS: This was a retrospective observational cohort study of the first year of N2 O 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 N2 O use were calculated as unadjusted and adjusted relative risks (RRs). Poisson regression was used to model the association between N2 O use and subsequent use of neuraxial analgesia and type of birth for both nulliparous and multiparous patients.

RESULTS: Overall, 20.2% of patients used N2 O during labor. Multiparous patients were 24% less likely to use N2 O than nulliparous patients (RR, 0.76; 95% CI, 0.69-0.84). Use of N2 O 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, N2 O 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 N2 O use and use of neuraxial analgesia in nulliparous patients (RR, 0.99; 95% CI, 0.93-1.06). N2 O use was not associated with cesarean birth in either group.

DISCUSSION: N2 O 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.