Oxygen saturation (SO2) - in capillaries and venules -
a measure for oxygen extraction
Hemoglobin amount (Hb amount) -
in microvessels (up to about 100µm)
Clinical Relevance
Normal microcirculation
Measurement of:
Hypoxia caused by venous congestion
During venous congestion
blood volume increases (especially in the venous system) and due to the decreased
perfusion pressure difference the blood flow decreases and with it the oxygen
saturation.
Hypoxia caused by ischemia
Flow and hemoglobin volume decreases, so that oxygen extraction increases with constant metabolism and oxygen saturation decreases.
Hypoxia caused by increased metabolism (Tumour, Inflammation)
Oxygen extraction increases. Therefore oxygen saturation decreases. With strongly increased metabolism additionally flow is increased to serve increased O2-demand.
