SKIN BLOOD-FLOW INFLUENCES THE TRANSCUTANEOUS PCO2 (TC PCO2) DURING STRESS IN THE GUINEA-PIG

The transcutaneously measured carbon dioxide tension (tc PCO2) allows fetal monitoring in a continuous and non-invasive way. Though tc PCO2 is correlated well with the fetal acid-base balance. rather large vari ations in tc PCO2 exist. A decreased skin blood flow is known to influ ence the transcutaneous oxygen tension (tc PO2), and tc PCO2 might be affected in an equal way. During fetal asphyxia skin blood flow is ext remely reduced. Thus, tc PCO2 might be affected by fetal asphyxia. whi ch it is supposed to detect. To elucidate the role of reduced skin per fusion on tc PCO2, experiments on acutely instrumented guinea pigs wer e performed and skin perfusion was changed by injection of catecholami nes. During control re PCO2 was twice as high as the arterial PCO2 due to a reduced skin perfusion. After injection of catecholamines skin b lood flow rose, tc PCO2 fell and the arterio-transcutaneous difference in PCO2 decreased. Then skin perfusion decreased and tc PCO2 increase d. We conclude, that during stress situations with a low skin perfusio n, as in the acutely instrumented guinea pig, re PCO2 is higher than t he arterial PCO2 and can be influenced by changes in skin blood flow. These findings are relevant for the interpretation of tc PCO2 recordin gs during fetal asphyxia, where an extreme vasoconstriction exists.