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

2020 
OBJECTIVE We tested the hypothesis that a longer duration of supplemental oxygen (O2) exposure in labor is associated with higher umbilical cord O2 content. STUDY DESIGN This is a planned secondary analysis of a randomized noninferiority trial comparing O2 to room air (RA) in laboring patients. Patients were randomized to 10 L/min O2 or RA at any point in active labor when they developed a Category II tracing that otherwise required resuscitation. The primary outcome for this analysis was umbilical vein (UV) pO2. The secondary outcome was umbilical artery (UA) pO2. These outcomes were compared between patients with short and long durations of O2 exposure, defined as <75th percentile and ≥75th percentile of duration, respectively. Outcomes were also compared between RA, short O2, and long O2 groups. RESULTS Among the 99 patients with paired and validated cord gases included in this analysis, UV pO2 was significantly lower in patients who received longer durations of O2 compared to those who received shorter durations (median [IQR] 25.5[21.5,33] vs 32.5 [26.5, 37.5] mm Hg, p 0.03). There was no difference in UA pO2 or other cord gases between short and long duration O2 groups. Other methods of intrauterine resuscitation were similar between short and long duration O2 groups. There was no difference in UA or UV pO2 when compared between RA, short duration O2, and long duration O2 groups. CONCLUSION Long durations of O2 exposure are not associated with higher cord pO2. In fact, patients with longer O2 exposure had lower UV pO2, suggesting impaired placental O2 transfer with prolonged O2 exposure.
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