Central venous oxygen saturation, or ScvO2, is one of the most misunderstood hemodynamic variables in critical care. Many clinicians recognize low values as concerning but are less comfortable interpreting normal or elevated measurements.
To understand ScvO2, it helps to revisit the Fick principle. Oxygen delivery is determined primarily by cardiac output, hemoglobin concentration, and arterial oxygen content.
Oxygen consumption reflects tissue metabolic demand. ScvO2 represents the balance between oxygen delivery and oxygen utilization.
A low ScvO2 generally indicates that tissues are extracting a greater proportion of delivered oxygen. This may occur because oxygen delivery is inadequate or because oxygen consumption has increased substantially.