A method and apparatus for determining a venous oxygen saturation value (SvO2) of a subject is provided. The method includes the steps of: a) sensing a plurality of tissue regions on a subject using a NIRS oximeter adapted to determine a tissue oxygen saturation value (StO2) for each region, each region independent of the other regions and each region sensed using a NIRS oximeter sensor specific to that region, and determining a StO2 value for that region b) assigning a coefficient to each region, each of which coefficients reflects a portion of the StO2 value for the region attributable to a composite venous blood return representative of the tissue regions measured and c) determining a composite SvO2 value for the subject using the StO2 region values and the respective coefficients.
