\text{Oxygen Content of blood} = \left [\text{Hb} \right] \left ( \text{g/dl} \right ) \ \times\ 1.34 \left ( \text{ml}\ O_2 /\text{g of Hb} \right ) \times\ O_2^{\text{saturation fraction}} +\ 0.0032\ \times\ P_{O_2} (\text{torr}) .
Cardiac output may also be estimated with the Fick principle using production of carbon dioxide as a marker substance [REF].