Fetal scalp blood flow as recorded by laser Doppler flowmetry and transcutaneous PO 2 during labour

Abstract

Laser Doppler flowmetry was used to evaluate the relationship between the changes in scalp blood flow and transcutaneous PO 2 ( PtcO 2) during labour. Laser Doppler flow (LDF) and PtcO 2 were measured simultaneously in fourteen women using a combined sensor. Scatter diagrams of LDF and PtcO 2 show a hyperbolic curve, i.e. at high flow levels Ptco 2 is independent of the flow rate and will reflect the arterial PO 2 value, whereas at lower flow levels PtcO 2 becomes highly dependent on the blood flow rate. The latter situation occurred in most of the fetuses when labour progressed. An inverse relationship between LDF and PtcO 2 was observed in two fetuses in those parts of the recordings which coincided with repetitive severe variable decelerations in the FHR tracing ( r = −0.59 and −0.65), suggesting a compensatory increase in scalp blood flow during hypoxemia. It is concluded that the PtcO 2 signal is considerably influenced by local scalp blood flow in the majority of the patients and thus is a questionable parameter for monitoring fetal carotid arterial PO 2.