What is the approximate partial pressure of oxygen in arterial blood (PaO2) in a healthy person at sea level?

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Multiple Choice

What is the approximate partial pressure of oxygen in arterial blood (PaO2) in a healthy person at sea level?

Oxygen dissolved in arterial blood (PaO2) shows how effectively oxygen moves from the lungs into the blood. In a healthy adult breathing room air at sea level, PaO2 is about 95–100 mmHg because the alveolar oxygen tension is around 100 mmHg and only a small A–a gradient exists. If you plug typical values into the alveolar gas equation (FiO2 ≈ 0.21, barometric pressure ≈ 760 mmHg, water vapor ≈ 47 mmHg, PaCO2 ≈ 40 mmHg, respiratory quotient ≈ 0.8), the alveolar PO2 comes out near 100 mmHg. The arterial PO2 is then slightly lower, commonly around 95–100 mmHg in a healthy person on room air. The other ranges would indicate abnormal oxygenation: about 40–45 mmHg points to hypoxemia, 70–80 mmHg can occur with aging or mild impairment but isn’t normal in a young healthy adult, and 110–120 mmHg would require unusually high inspired oxygen or specific conditions.

Oxygen dissolved in arterial blood (PaO2) shows how effectively oxygen moves from the lungs into the blood. In a healthy adult breathing room air at sea level, PaO2 is about 95–100 mmHg because the alveolar oxygen tension is around 100 mmHg and only a small A–a gradient exists.

If you plug typical values into the alveolar gas equation (FiO2 ≈ 0.21, barometric pressure ≈ 760 mmHg, water vapor ≈ 47 mmHg, PaCO2 ≈ 40 mmHg, respiratory quotient ≈ 0.8), the alveolar PO2 comes out near 100 mmHg. The arterial PO2 is then slightly lower, commonly around 95–100 mmHg in a healthy person on room air.

The other ranges would indicate abnormal oxygenation: about 40–45 mmHg points to hypoxemia, 70–80 mmHg can occur with aging or mild impairment but isn’t normal in a young healthy adult, and 110–120 mmHg would require unusually high inspired oxygen or specific conditions.

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