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O2 delivery vs. PaO2

Oxygen delivery is defined as the amount of oxygen delivered to the capillaries per minute. It is calculated by the following formula:

DO2=CO x CaO2 (mL/min/m2)

So oxygen delivery is dependent on cardiac output as well as the arterial oxygen content.

The arterial oxygen content is based on the amount of hemoglobin (Hb), the saturation of hemoglobin with oxygen (SaO2), and the amount of oxygen that each gram of hemoglobin can carry, which has been calculated to be between 1.32 and 1.39, depending on the circumstances. This is summarized by the equation below:

CaO2=(1.34 X Hgb X SaO2) + (0.003 X PaO2)

Therefore, oxygen delivery can be affected by changes in cardiac output as well as changes in the oxygen saturation of hemoglobin, the amount of hemoglobin available, and to a much smaller extent the PaO2 (the amount of oxygen dissolved in the blood). Thus, when hemoglobin is completely saturated with oxygen (the SaO2 is 1.0 or 100%), increases in the PaO2 have a negligible impact on the CaO2 and oxygen delivery.