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) in intrauterine resuscitation, the obstetric scientists' understanding of O therapy is full of contradictions. We tested the hypothesis that higher maternal arterial partial pressure of oxygen (PO) is associated with higher umbilical cord venous PO (UvPO).

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 or room air from the onset of second stage to delivery. We reported that maternal 2 L/min O 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 exposure increased the maternal arterial PO to the median 150 mmHg (hemoglobin would be saturated). The primary outcome for this analysis was UvPO in these non-random samples.

RESULTS

There were no significant differences between the O group (N = 107) and the control group (N = 110) in the UvPO (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 exposure duration (< 25th, ≧ 25th < 50th, ≧ 50th < 75th, ≧ 75th percentile) in the UvPO.

CONCLUSIONS

Maternal O exposure at super-physiological levels (median arterial blood PO 150 mmHg) in normal labor may not change the UvPO.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov NCT02221440 , first posted in 20 August 2014.