A comparative study of continuous intravascular O2 saturation and transcutaneous PO2 measurements in the sheep fetus following the reduction of uterine blood flow.

Under physiologic conditions the tcPO2 reflects the PO2 in the carotid artery. It is therefore a measure of the PO2 in the arteries supplying the brain. The response of the tcPO2 to fetal hypoxemia, as during the recovery period following hypoxemia, is delayed. The delayed response of the tcPO2 during recovery is generated by the release of catecholamines into the fetal circulation. The reading of the tcPO2 corresponds better with the course of the heart rate decelerations and the increased blood pressure than with the course of the PO2 in the fetal aorta. The tcPO2 is, in this context, a reliable measure for the peripheral oxygenation and vasoconstriction. The tcPO2 however should be applied with great care for studying the pathomechanism of fetal heart rate decelerations during labor.