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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.

      Key words

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      Linked Article

      • Potential benefits of maternal supplemental oxygen
        American Journal of Obstetrics & GynecologyVol. 224Issue 3
        • Preview
          Watkins et al1 suggest that longer durations of O2 exposure result in lower PO2 in the umbilical vein, suggesting O2-induced impaired placental O2 transfer, although previous trials indicate that maternal O2 administration increases umbilical vein PO2. Under conditions of maternal normoxia, supplemental maternal O2 increases maternal arterial PO2, minimally alters maternal arterial O2 content, and results in a modest increase in fetal umbilical vein PO2. Should the mother be significantly hypoxemic, O2 supplementation has a markedly greater beneficial effect. In this study, patients with maternal hypoxia were excluded from enrollment, thus limiting the benefit of supplemental O2.
        • Full-Text
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      • Duration of oxygen exposure: insight and response to feedback
        American Journal of Obstetrics & GynecologyVol. 224Issue 3
        • Preview
          We thank Dr Ross for his letter and interest in our study investigating the duration of maternal O2 exposure and umbilical cord O2 content.1
        • Full-Text
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