Continuous monitoring of tissue oxygen tension during hyperoxia and hypoxia: relation of subcutaneous, transcutaneous, and conjunctival oxygen tension to hemodynamic variables.

Subcutaneous, transcutaneous, and conjunctival oxygen tensions (PscO2, PtcO2, and PcjO2, respectively) were measured in anesthetized dogs subjected sequentially to normoxia, hyperoxia, and hypoxia. Intravascular pressure, hemodynamic and oxygen transport variables were measured simultaneously. PtcO2 and PcjO2 closely paralleled PaO2 during normoxia, hyperoxia, and hypoxia over a wide range of arterial oxygen tensions. PtcO2 was reliable over the widest range of PaO2, with a correlation coefficient of .94. The PcjO2/PaO2 index fell at very low PaO2. The PscO2/PaO2 index decreased at both very low and very high PaO2. Only minor changes were found in hemodynamic and oxygen transport variables during hyperoxia. During hypoxia, however, cardiac output and other central hemodynamic measurements increased, while PscO2, PtcO2, and PcjO2 fell. Oxygen delivery and oxygen consumption were maintained or only slightly changed during hypoxia. All three continuous measurements of oxygen tension are reliable indices of PaO2 over a wide range under normovolemic conditions. The instruments for measuring PscO2 and PcjO2 are unheated and therefore may have advantages for human application.