The mixed venous oxygen content (CvO2) is calculated using which formula?

The mixed venous oxygen content (CvO2) is calculated using which formula?

• A. (Hb × 1.34 × SvO2) + (PvO2 × 0.003)
• B. (Hb × 1.34 × SvO2) + (PaO2 × 0.003)
• C. (Hb × 1.34 × SaO2) + (PvO2 × 0.003)
• D. (Hb × 1.34 × SvO2) + (PvO2 × 0.0035)

Answer: (A)

Oxygen content in mixed venous blood has two parts: the amount bound to hemoglobin and the amount dissolved in plasma. The bound portion depends on how much hemoglobin there is and how saturated it is with oxygen in the venous blood (SvO2). The dissolved portion depends on the venous PO2 (PvO2) and the solubility of oxygen in plasma. Put together, the equation is CvO2 = (Hb × 1.34 × SvO2) + (PvO2 × 0.003). This uses SvO2 and PvO2—the venous saturation and venous PO2—along with the standard solubility coefficient of 0.003 mL O2 per dL of blood per mmHg. That’s why this option is correct: it incorporates the venous saturation and venous PO2 with the correct solubility constant. Using PaO2 or arterial saturation would mix in arterial variables, and the solubility coefficient is 0.003, not 0.0035. For context, if Hb is 15 g/dL, SvO2 is 0.70, and PvO2 is 40 mmHg, CvO2 ≈ 15 × 1.34 × 0.70 + 40 × 0.003 ≈ 14.2 mL/dL, which aligns with typical venous oxygen content values.

Oxygen content in mixed venous blood has two parts: the amount bound to hemoglobin and the amount dissolved in plasma. The bound portion depends on how much hemoglobin there is and how saturated it is with oxygen in the venous blood (SvO2). The dissolved portion depends on the venous PO2 (PvO2) and the solubility of oxygen in plasma. Put together, the equation is CvO2 = (Hb × 1.34 × SvO2) + (PvO2 × 0.003). This uses SvO2 and PvO2—the venous saturation and venous PO2—along with the standard solubility coefficient of 0.003 mL O2 per dL of blood per mmHg.

That’s why this option is correct: it incorporates the venous saturation and venous PO2 with the correct solubility constant. Using PaO2 or arterial saturation would mix in arterial variables, and the solubility coefficient is 0.003, not 0.0035. For context, if Hb is 15 g/dL, SvO2 is 0.70, and PvO2 is 40 mmHg, CvO2 ≈ 15 × 1.34 × 0.70 + 40 × 0.003 ≈ 14.2 mL/dL, which aligns with typical venous oxygen content values.