Raghuraman N, Temming LA, Doering MM, et al. Maternal oxygen supplementation compared with room air for intrauterine resuscitation: a systematic review and meta-analysis. JAMA Pediatr. January 4, 2021. doi:10.1001/jamapediatrics.2020.5351.
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Maternal oxygen supplementation is widely used in labor for nonreassuring fetal heart rate (FHR) tracings, although its efficacy is uncertain for preventing fetal acidosis, operative intervention, or sequelae of neonatal encephalopathy. Recently, Raghuraman and colleagues reported the results of a systematic review and meta-analysis that included 16 randomized controlled trials. A total of 1,078 women were included in the oxygen group and 974 in the room air group. The primary outcome was umbilical artery pH; 14 trials reported on this outcome.
After analyzing the pooled and stratified results of the effect of maternal oxygen supplementation versus room air on umbilical artery gas measures, the authors concluded that peripartum oxygen supplementation is not associated with clinically relevant improvement in umbilical artery pH. They acknowledged, however, that the published studies were heterogeneous, lacked data on the association of oxygen supplementation with neonatal outcome, and did not assess oxygen use for abnormal FHR tracings, except for one trial with category II FHR tracings.
Effects of O2 supplementation
As maternal arterial hemoglobin is nearly saturated under normal conditions, maternal hyperoxia produces only modest increases in umbilical vein Po2 and O2 content during maternal normoxemia but greater effects during maternal hypoxemia (FIGURE).1 Maternal O2 supplementation will impact fetal oxygenation depending on the extent of O2 supplementation and the normality of maternal, placental, and fetal O2 transport steps.2
Fetal hypoxemia and acidosis can result from an interruption or an impairment of the mother-to-placenta-to-fetus oxygen pathway. With some interruptions of the oxygen pathway, such as placental abruption and complete cord occlusion–induced bradycardia, there would be less impact of maternal hyperoxia. By contrast, with other oxygen pathway impairments, such as reduced oxygen transfer with placental insufficiency, maternal hyperoxia can be of greater value by increasing maternal uterine artery and vein Po2 and, thus, the placental O2 transfer.
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