Arterial Oxygen Content

Arterial Oxygen Content (CaO2) is the amount of oxygen bound to hemoglobin (1.34 * Hb * SaO2) plus the oxygen dissolved in plasma (0.0031 * PaO2).

The normal oxygen combining capacity is 1.39 mls/gram, however due to abnormal forms of hemoglobin such as carboxyhemoglobin and methemoglobin this value is reduced to 1.34 mls/gram.

Hgb is Hemoglobin, the normal Hgb for males is 14-20 g/dl and females 12-15 g/dl. Hgb expressed as g/dl is equivalent to g Hgb/100 mL of Blood.

SaO2 is the percentage of available hemoglobin that is saturated with oxygen, this value is from a direct measurement of an arterial blood gas.

0.0031 is the solubility coefficient of oxygen at body temperature.

PaO2 is the Partial Pressure of Oxygen (Alveolar Gas Equation) in arterial blood not bound to hemoglobin.

Arterial Oxygen Content – CaO2 Calculator

Example CaO2 Exam Calculation

Calculate the Arterial Oxygen Content given the following: Hgb 14 g Hgb/100 ml blood, SaO2=95%,and PaO2 = 120 mmHg.

CaO2 = (Hgb * 1.34 * SaO2/100) + ( 0.0031* PaO2)

CaO2 = (14 g Hgb/100 ml blood * 1.34 ml O2/ g Hgb * 95%/100) + ( 0.0031 ml O2/100 ml blood/mmHg* 120 mmHg)

CaO2 = (18.76 ml O2/ 100 ml blood * 0.95) + 0.372 ml O2/100 ml blood

CaO2 = 17.82 ml O2/ 100 ml blood + 0.372 ml O2/100 ml blood

CaO2 = 18.19 ml O2/ 100 ml blood

CaO2 = 18.19 vol%