Scalp Blood Flow Measured by the Xenon Clearance Technique and Transcutaneous PO2 in the Fetal Lamb

Summary: Scalp blood flow and transcutaneous (tc) Po2 were measured in four fetal lambs at 130–135 days of gestation. Scalp blood flow was measured by the xenon clearance technique using a technetium source to correct for changes in distance from the detector. The effect of circular pressure, the so-called “tonsure effect” on scalp flow and tcPo2, was evaluated by pressing a ring on the scalp. A circular pressure between 20–30 mmHg markedly reduced local scalp blood flow and was sufficient to reduce tcPo2 to zero. We found evidence of significant recirculation of xenon in the fetal circulation indicating right-left shunting. This study showed that the tonsure effect seriously affected scalp blood flow and tcPo2 in the fetus.