The duration of intrapartum supplemental oxygen administration and umbilical cord oxygen content

Background: Maternal oxygen (O₂) administration is a commonly performed intrauterine resuscitation technique though to improve fetal oxygenation. However, hyperoxygenation is known to be harmful in both neonates and adults. Currently, there are no formal recommendations on whether a certain dose or duration of O₂ may be most helpful in improving umbilical cord gases or neonatal outcomes. Objective: We tested the hypothesis that prolonged supplemental O₂ exposure during labor is associated with increased umbilical cord O₂ concentrations. Study Design: This was a planned secondary analysis of a randomized noninferiority trial comparing O₂ with room air in laboring patients. Patients were randomized to receive either 10 L/min O₂ or room air at any point during active labor when they developed a category II fetal heart tracing that would otherwise require resuscitation. The primary outcome variable for this analysis was partial pressure of O₂ in the umbilical vein. The secondary outcome variable was partial pressure of O₂ in the umbilical artery. These outcome variables were compared between patients with short durations of O₂ exposure and those with long durations of O₂ exposure, defined as <75th percentile and ≥75th percentile of duration, respectively. The outcomes were also compared among the groups that received room air, O₂ for short durations, and O₂ for long durations. Results: Among the 99 patients with paired and validated cord gases who were included in this analysis, the partial pressure of O₂ in the umbilical vein was significantly lower in patients who received O₂ supplementation for longer durations than in those who received O₂ for shorter durations (median interquartile range 25.5 [21.5–33] vs 32.5 [26.5–37.5] mm Hg; P<.03). There was no difference in the partial pressure of O₂ in the umbilical artery or other cord gases between the short and long duration O₂ supplementation groups. Other methods of intrauterine resuscitation were similar between the short and long duration O₂ supplementation groups. There was no difference in the partial pressure of O₂ in the umbilical artery or in the umbilical vein when the room air, short duration O₂ supplementation, and long duration O₂ supplementation groups were compared. Conclusion: Longer durations of O₂ exposure are not associated with a higher partial pressure of O₂ in the umbilical cord. In fact, patients with longer durations of O₂ exposure had lower partial pressure of O₂ in the umbilical vein, suggesting impaired placental O₂ transfer with prolonged O₂ exposure.