Which is the acceptable A-aDO2 range at FiO2 0.21?

Which is the acceptable A-aDO2 range at FiO2 0.21?

• A. 10-15 mmHg
• B. 5-10 mmHg
• C. 0-5 mmHg
• D. 15-20 mmHg

Answer: (A)

The short answer is that the alveolar-arterial oxygen gradient should be small on room air, since the lungs normally transfer oxygen efficiently into the blood. At sea level with FiO2 of 0.21, the alveolar PO2 is about 100 mmHg, and arterial PO2 is only slightly lower, giving a modest gradient. In healthy adults this gradient is typically around 5 to 15 mmHg, with many individuals near 10 mmHg. So a range of 10–15 mmHg best reflects the common normal value for A-aDO2 at FiO2 0.21. Values lower than this would be unusually small, while values starting around 15–20 mmHg begin to approach ranges considered elevated, especially in younger people, making 10–15 mmHg the most representative normal band.

The short answer is that the alveolar-arterial oxygen gradient should be small on room air, since the lungs normally transfer oxygen efficiently into the blood. At sea level with FiO2 of 0.21, the alveolar PO2 is about 100 mmHg, and arterial PO2 is only slightly lower, giving a modest gradient. In healthy adults this gradient is typically around 5 to 15 mmHg, with many individuals near 10 mmHg. So a range of 10–15 mmHg best reflects the common normal value for A-aDO2 at FiO2 0.21. Values lower than this would be unusually small, while values starting around 15–20 mmHg begin to approach ranges considered elevated, especially in younger people, making 10–15 mmHg the most representative normal band.