Redistribution of fetal circulation during repeated asphyxia in sheep: effects on skin blood flow, transcutaneous PO2, and plasma catecholamines.

To improve the understanding of fetal responses to labour, we have ascertained whether reduced fetal skin blood flow after asphyxia reflects redistribution of the circulation, and if so, whether this can be detected by transcutaneous PO2 monitoring. We also studied the relation between plasma concentrations of catecholamines and organ blood flow. Eight experiments were conducted on 8 acutely-prepared fetal sheep in utero between 125 and 135 days of gestation. In each fetus 11 episodes of asphyxia were induced within 33 min by intermittent arrest of uterine blood flow for 90 s. The distribution of blood flow was measured before and after asphyxia (at 35.5 min) by the isotope-labelled microsphere method. Blood samples were drawn at 0, 33 (i.e. after 90 s recovery), and 40 min to determine blood gases, acid-base balance, and catecholamine concentrations. Fetal transcutaneous PO2, heart rate, arterial blood pressure, and arterial O2 saturation were recorded continuously. Repeated fetal asphyxia increased plasma catecholamine concentrations and caused a circulatory redistribution to the brain (181% change), adrenals (116% change), and lungs (105% change) at the expense of many peripheral organs, particularly of the skin (-61% change). The pattern of these changes was different from that observed by others in persistent hypoxia or asphyxia. The decrease in skin blood flow, which depressed transcutaneous PO2 and increased the arterial-transcutaneous PO2 difference, correlated with the decrease in blood flow to other peripheral organs and with an increase in blood flow to the brain stem. We conclude that reduced blood flow to the fetal skin after repeated episodes of asphyxia indicates circulatory redistribution, which can be detected by transcutaneous PO2 measurements. We suggest that monitoring of variables that depend on skin blood flow may improve fetal surveillance during complicated labour.