NBRC Normal Values TMC Practice Test

PaO2 varies directly with FiO2. Which option expresses this correctly?

PaO2 is fixed and does not depend on FiO2 PaO2 varies inversely with FiO2 PaO2 varies directly with FiO2 PaO2 is independent of FiO2

Correct Answer:

PaO2 varies directly with FiO2

Explanation:

The main idea is that arterial oxygen tension (PaO2) increases when the inspired oxygen fraction (FiO2) is raised. In the alveolar gas equation, PAO2 depends on FiO2; increasing FiO2 raises the oxygen available to diffuse into the blood, so PaO2 tends to rise as well. This is why giving supplemental oxygen improves arterial oxygen tension, especially in those with hypoxemia. While the exact increase can be influenced by lung diffusion capacity and V/Q matching, the overall relationship is direct: higher FiO2 leads to higher PaO2.

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