Comparison of continuous transcutaneous Po2 measurement with intermittent arterial Po2 determinations in fetal lambs

This study determined the validity of transcutaneous Po2 (tcPo2) versus Pao2 determinations in the sheep fetus. In 7 fetal lambs catheters were placed in the carotid artery and the trachea, and ECG leads and a tcPo2 electrode were attached. Intermittently determined Pao2 values were compared to continuously recorded tcPo2 values. Fetal tcPo2 values ranging from 12 to 29 mmHg were achieved by changing the gas mixture the ewe breathed or by inflation of a balloon catheter in the maternal aorta. Transcutaneous Po2 correlated strongly with Pao2 (r = .91). These studies indicate that the tcPo2 electrode precisely and accurately reflects Pao2 in the fetal lamb. Limitations of tcPo2 measurements regarding prolonged attachment of the electrode to the fetal skin as well as fetal skin tolerance to the heat of the electrode have been identified. With this electrode the changes in oxygen tension can be compared with changes in fetal cardiovascular variables, eg, heart rate, blood pressure, and ECG, for a better understanding of the effects of hypoxemia on the fetus.