What is the normal A-a DO2 on 100% oxygen?

What is the normal A-a DO2 on 100% oxygen?

• A. 5-10 torr
• B. 0-5 torr
• C. 25-65 torr
• D. 60-100 torr

Answer: (C)

The A-a gradient shows how well oxygen moves from the alveoli into the arterial blood. On 100% oxygen, PAO2 is very high, but PaO2 cannot rise perfectly due to physiologic shunt and V/Q mismatch, so the gradient stays elevated but within a normal upper range. In healthy individuals, the normal A-a gradient on 100% O2 is about 25–65 torr. Values higher than this suggest some impairment in oxygen transfer, while much lower values aren’t expected on 100% O2.

The A-a gradient shows how well oxygen moves from the alveoli into the arterial blood. On 100% oxygen, PAO2 is very high, but PaO2 cannot rise perfectly due to physiologic shunt and V/Q mismatch, so the gradient stays elevated but within a normal upper range. In healthy individuals, the normal A-a gradient on 100% O2 is about 25–65 torr. Values higher than this suggest some impairment in oxygen transfer, while much lower values aren’t expected on 100% O2.