Searching for non-invasive markers of tissue hypoxia

Tissue hypoxia is a common end product of circulatory shock and a primary target for resuscitation efforts. In this issue Podbregar and Mozina show that thenar tissue O(2 )saturation (StO(2)) and mixed venous O(2 )saturation (SvO(2)) co-vary in patients in left ventricular failure, but in patients with sepsis StO(2 )was higher than SvO(2). Although StO(2 )may co-vary with SvO(2 )they have different determinants such that after shock StO(2 )may increase well before SvO(2 )as a result of increased O(2 )demands to repay O(2 )debt incurred during hypoperfusion. Thus, the use of StO(2 )alone to define the endpoint of resuscitation may be misleading.