Transcutaneous PO2 and cardiovascular observations in the sheep fetus following the reduction of uterine blood flow.

On 11 near term pregnant sheep the response of the fetal transcutaneous oxygen partial pressure (tcPO2) was compared with the alteration of the oxygen saturation (SO2) and the PO2 in the fetal aorta (FA), fetal heart rate (FHR) and fetal arterial blood pressure (FA BP) following the reduction of uterine blood flow (UBF). The FA SO2 changed 12.3 (SD 3.1) sec and the tcPO2 26.6 (SD 7.9) sec after UBF was reduced. The tcPO2 response was also delayed after UBF was restored: 72.6 (SD 41.9) sec compared to the SO2 response: 23.9 (SD 14.4) sec. The reduction of UBF was paralleled by a rise of the FA BF and a fall of FHR. They were at control within 10 min after the reduction of UBF was released reflecting the normalization of the tcPO2. There was a tcPO2-FA PO2-difference which was due to the difference that exist between the carotid artery PO2 and the PO2 in the fetal aorta. The delayed response of the tcPO2 electrode was due to the response time of the electrode itself. The delay during the recovery period however was predominantly due to the peripheral vasoconstriction as proved by Norepinephrine injection. The tcPO2 reflects very close the fall of the FA BP and the rise of the FHR during the recovery period and vice versa. The importance of the tcPO2-PO2,a difference for the fetal condition during labor has still to be worked out.