PAO2 calculation using FiO2 0.50, PaCO2 45, and R = 0.8 at sea level yields PAO2 approximately which value?

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Multiple Choice

PAO2 calculation using FiO2 0.50, PaCO2 45, and R = 0.8 at sea level yields PAO2 approximately which value?

The alveolar gas equation governs PAO2: PAO2 = FiO2 × (Pb − PH2O) − PaCO2 × (1 − R). At sea level, Pb ≈ 760 mmHg and PH2O ≈ 47 mmHg. With FiO2 = 0.50 and PaCO2 = 45 with R = 0.8: First part: 0.50 × (760 − 47) = 0.50 × 713 ≈ 356.5 mmHg Second part: 45 × (1 − 0.8) = 45 × 0.2 = 9 mmHg PAO2 ≈ 356.5 − 9 ≈ 347.5 mmHg, about 350 mmHg. So the PAO2 is approximately 350 mmHg.

The alveolar gas equation governs PAO2: PAO2 = FiO2 × (Pb − PH2O) − PaCO2 × (1 − R). At sea level, Pb ≈ 760 mmHg and PH2O ≈ 47 mmHg. With FiO2 = 0.50 and PaCO2 = 45 with R = 0.8:

First part: 0.50 × (760 − 47) = 0.50 × 713 ≈ 356.5 mmHg

Second part: 45 × (1 − 0.8) = 45 × 0.2 = 9 mmHg

PAO2 ≈ 356.5 − 9 ≈ 347.5 mmHg, about 350 mmHg.

So the PAO2 is approximately 350 mmHg.

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