What is the normal A-a DO2 on room air (21%)?

What is the normal A-a DO2 on room air (21%)?

• A. 25-65 torr
• B. 0-5 torr
• C. 15-25 torr
• D. 5-10 torr

Answer: (D)

The normal A-a DO2 on room air shows how well oxygen moves from the alveoli into the arterial blood. It’s the difference between the oxygen tension in the alveoli (PAO2) and the oxygen tension in arterial blood (PaO2). On room air, PAO2 is about 100 mmHg when using the typical alveolar gas equation, and a healthy person’s PaO2 is roughly 95–100 mmHg, giving an A-a gradient of about 5–10 mmHg. This small gradient indicates efficient gas exchange. In pediatrics, the normal gradient is generally ≤15 mmHg, so a value in the 5–10 range is considered normal. If the gradient were much higher, it would point to gas exchange abnormalities such as V/Q mismatch, diffusion limitation, or shunt. Therefore, 5–10 torr is the best representation of a normal A-a DO2 on room air.

The normal A-a DO2 on room air shows how well oxygen moves from the alveoli into the arterial blood. It’s the difference between the oxygen tension in the alveoli (PAO2) and the oxygen tension in arterial blood (PaO2). On room air, PAO2 is about 100 mmHg when using the typical alveolar gas equation, and a healthy person’s PaO2 is roughly 95–100 mmHg, giving an A-a gradient of about 5–10 mmHg. This small gradient indicates efficient gas exchange. In pediatrics, the normal gradient is generally ≤15 mmHg, so a value in the 5–10 range is considered normal. If the gradient were much higher, it would point to gas exchange abnormalities such as V/Q mismatch, diffusion limitation, or shunt. Therefore, 5–10 torr is the best representation of a normal A-a DO2 on room air.