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Approximately 2/3 of laboring women receive supplemental oxygen (O2) in an attempt to reverse perceived fetal hypoxemia and prevent acidosis. O2 supplementation is routinely used in patients with Category II fetal heart tracings (FHT). However, this liberal use of intrapartum O2 may not be beneficial, particularly since hyperoxygenation in neonates is harmful. We tested the hypothesis that room air (RA) for Category II FHT is not worse than O2 in reducing umbilical artery (UA) lactate, a marker of metabolic acidosis and neonatal morbidity.
This was a randomized controlled noninferiority trial conducted from June 2016 to June 2017. Singleton pregnancies ≥ 37 weeks with Category II FHT necessitating intrauterine resuscitation in active labor (≥6cm) were randomized to RA or 10L/min O2 by face mask until delivery. The primary outcome was UA lactate measured by cord gases collected at delivery. Secondary outcomes were other UA gas components, cesarean delivery for nonreassuring fetal status (NRFS), and operative vaginal delivery. Assuming a mean UA lactate of 3.5 ± 1.6 mmol/L in patients with Category II FHT, 98 patients were needed for 90% power to detect non-inferiority with a margin of 30% and 1-sided alpha of 0.025. We increased the sample size to 114 patients to accommodate 15% loss to unattainable cord gases. Noninferiority was declared if the mean difference in lactate between RA and O2 was <1.0 mmol/L. Analysis was by intention-to-treat.
Of the 114 patients randomized, 99 with paired cord gases were included in the intention-to-treat analysis; 48 O2 and 51 RA. There was no difference in mean UA lactate between patients randomized to O2 and RA (mean [95%CI], 3.4 [3.0, 3.8] vs 3.5 [3.1, 4.0]), P=0.69). The mean difference in UA lactate was 0.1 mmol/L (95% CI -0.5, 0.7), which is within the non-inferiority margin (Figure). There were no differences in other UA gas components, operative vaginal delivery or cesarean delivery for NRFS between groups (Table).
Among patients with Category II FHT in active labor, intrauterine resuscitation with RA is not inferior to O2 in improving UA lactate. (ClinicalTrials.gov number NCT02741284).