Transcutaneous O2 and CO2 Monitoring

Abstract

Transcutaneous PO2 and PCO2 measurements are often used to estimate their arterial counterparts. However, tissue perfusion is a critical determinant of the difference between transcutaneous and arterial PO2 or PCO2. Measuring transcutaneous PO2 at 37 °C poorly represents tissue oxygenation, as the measured variable reflects a mixture of arterial, venous, and capillary PO2, and the proportion of these varies in different shock states. Dynamic tests, such as transient occlusion test or inhalation of a hyperoxic mixture, are much more representative of tissue perfusion. On the other hand, transcutaneous PCO2 at 37 °C and the gradient between transcutaneous and arterial PCO2 reflect tissue perfusion and in particular microvascular perfusion. Whether these could be used in routine clinical monitoring of our critically ill patients remains to be determined.