With Hb = 15 g/dL, SaO2 = 90%, CO = 4 L/min, and PaO2 = 40 mmHg, what is the calculated DO2 (approx.) in mL/min?

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Multiple Choice

With Hb = 15 g/dL, SaO2 = 90%, CO = 4 L/min, and PaO2 = 40 mmHg, what is the calculated DO2 (approx.) in mL/min?

Oxygen delivery to the tissues (DO2) is determined by how much oxygen is carried in arterial blood (CaO2) and the amount of blood the heart pumps each minute (cardiac output). CaO2 is calculated from both the oxygen bound to hemoglobin and the dissolved oxygen in plasma: CaO2 = (Hb × 1.34 × SaO2) + (PaO2 × 0.003). Plugging in the values: - Hb × 1.34 × SaO2 = 15 × 1.34 × 0.90 ≈ 18.09 mL O2/dL - PaO2 × 0.003 = 40 × 0.003 = 0.12 mL O2/dL So CaO2 ≈ 18.21 mL O2 per dL of blood. Now convert cardiac output to compatible units. CO = 4 L/min = 40 dL/min. DO2 = CO × CaO2 ≈ 40 × 18.21 ≈ 728 mL O2/min. Note this result depends on proper unit handling: CaO2 is per deciliter, so CO must be expressed in deciliters per minute to multiply directly. A common pitfall is using CO in liters per minute without converting, which would yield a much smaller value (around 72 mL/min). The standard calculation gives about 730 mL/min. The options shown don’t align with the correct unit-consistent result.

Oxygen delivery to the tissues (DO2) is determined by how much oxygen is carried in arterial blood (CaO2) and the amount of blood the heart pumps each minute (cardiac output).

CaO2 is calculated from both the oxygen bound to hemoglobin and the dissolved oxygen in plasma: CaO2 = (Hb × 1.34 × SaO2) + (PaO2 × 0.003). Plugging in the values:

  • Hb × 1.34 × SaO2 = 15 × 1.34 × 0.90 ≈ 18.09 mL O2/dL

  • PaO2 × 0.003 = 40 × 0.003 = 0.12 mL O2/dL

So CaO2 ≈ 18.21 mL O2 per dL of blood.

Now convert cardiac output to compatible units. CO = 4 L/min = 40 dL/min. DO2 = CO × CaO2 ≈ 40 × 18.21 ≈ 728 mL O2/min.

Note this result depends on proper unit handling: CaO2 is per deciliter, so CO must be expressed in deciliters per minute to multiply directly. A common pitfall is using CO in liters per minute without converting, which would yield a much smaller value (around 72 mL/min). The standard calculation gives about 730 mL/min. The options shown don’t align with the correct unit-consistent result.

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