Continuous Fetal Scalp and Carotid Artery Oxygen Tension Monitoring in the Sheep.

Fetal scalp and carotid PO2 were recorded continuously by polargraphic oxygen electrodes at several levels of maternal oxygenation. The results were compared to measurements obtained by intermittent blood samples using the radiometer blood gas analyzer. There was a good correlation between the PO2 values measured by the implanted oxygen electrodes and by conventional analyses of blood samples collected anaerobically. Electrode measurements differed from the control radiometer values by a mean of +/- 1.2 mmHg; 2 SD= +/- 2.50. Scalp PO2 recordings were lower but paralleled the carotid recordings under varying degrees of maternally inspired O2 concentrations. Thus scalp PO2 levels reflect closely those in the central fetal circulation. Administration of 95% O2 to the mother resulted in a 27% increase of scalp PO2 and a 29% increase in the carotid artery PO2 when compare to room air.