Which formula correctly defines arterial oxygen content (CaO2)?

Which formula correctly defines arterial oxygen content (CaO2)?

• A. (Hb × 1.34 × SvO2) + (PvO2 × 0.003)
• B. (Hb × 1.34 × SaO2) + (PvO2 × 0.003)
• C. (Hb × 1.34 × SaO2) + (PaO2 × 0.003)
• D. (Hb × 1.23 × SaO2) + (PaO2 × 0.003)

Answer: (C)

Oxygen content in arterial blood comes from two parts: the oxygen bound to hemoglobin and the oxygen dissolved in plasma. The bound portion is Hb (in g/dL) times the maximum oxygen-carrying capacity per gram of Hb (about 1.34 mL O2/g Hb) times the arterial oxygen saturation (SaO2, as a fraction). The dissolved portion is PaO2 (in mmHg) times the solubility of oxygen in plasma (about 0.003 mL O2/dL per mmHg). Put together, CaO2 = (Hb × 1.34 × SaO2) + (PaO2 × 0.003). This uses arterial values (SaO2 and PaO2) and the standard constants. The other options mix venous values (SvO2, PvO2) or use an incorrect constant for Hb’s oxygen-carrying capacity, or pair the dissolved component with the wrong arterial/dissolved term, making them incorrect.

Oxygen content in arterial blood comes from two parts: the oxygen bound to hemoglobin and the oxygen dissolved in plasma. The bound portion is Hb (in g/dL) times the maximum oxygen-carrying capacity per gram of Hb (about 1.34 mL O2/g Hb) times the arterial oxygen saturation (SaO2, as a fraction). The dissolved portion is PaO2 (in mmHg) times the solubility of oxygen in plasma (about 0.003 mL O2/dL per mmHg). Put together, CaO2 = (Hb × 1.34 × SaO2) + (PaO2 × 0.003). This uses arterial values (SaO2 and PaO2) and the standard constants.

The other options mix venous values (SvO2, PvO2) or use an incorrect constant for Hb’s oxygen-carrying capacity, or pair the dissolved component with the wrong arterial/dissolved term, making them incorrect.