Maternal oxygen exposure may not change umbilical cord venous partial pressure of oxygen: non-random, paired venous and arterial samples from a randomised controlled trial

BACKGROUND: Despite the widespread use of oxygen (O(2)) in intrauterine resuscitation, the obstetric scientists’ understanding of O(2) therapy is full of contradictions. We tested the hypothesis that higher maternal arterial partial pressure of oxygen (PO(2)) is associated with higher umbilical cord venous PO(2) (UvPO(2)). METHODS: This is a planned secondary analysis of a randomised controlled trial (RCT), 443 normal women were 1:1 randomly allocated to receive 2 L/min O(2) or room air from the onset of second stage to delivery. We reported that maternal 2 L/min O(2) exposure cannot affect the umbilical cord arterial pH or the fetal heart rate (FHR) pattern. In 217 non-random samples, we found 2 L/min O(2) exposure increased the maternal arterial PO(2) to the median 150 mmHg (hemoglobin would be saturated). The primary outcome for this analysis was UvPO(2) in these non-random samples. RESULTS: There were no significant differences between the O(2) group (N = 107) and the control group (N = 110) in the UvPO(2) (median 30.2, interquartile 25.4–35.2 versus median 28.3, interquartile 23.4–35.3, mmHg, P = 0.379). There were also no significant differences between room air and different percentiles of O(2) exposure duration (< 25th, ≧ 25th < 50th, ≧ 50th < 75th, ≧ 75th percentile) in the UvPO(2). CONCLUSIONS: Maternal O(2) exposure at super-physiological levels (median arterial blood PO(2) 150 mmHg) in normal labor may not change the UvPO(2). CLINICAL TRIAL REGISTRATION: ClinicalTrials.govNCT02221440, first posted in 20 August 2014.