Compared with ambient air, supplemental oxygen increases FiO2 by raising it above what baseline percentage?

Compared with ambient air, supplemental oxygen increases FiO2 by raising it above what baseline percentage?

• A. Below 21%
• B. Zero change in FiO2 from baseline air
• C. Exactly 15%
• D. Above 21%

Answer: (D)

The key idea is that the oxygen content of room air is about 21%. When you give supplemental oxygen, you increase the fraction of inspired oxygen, so the FiO2 rises above that 21% baseline. Therefore, the correct understanding is that supplemental oxygen raises FiO2 above 21%. The other ideas don’t fit because room air already has its FiO2 at about 21%, so it wouldn’t be described as below that, and providing oxygen does not keep FiO2 at the exact same level. An exact value like 15% would be lower than ambient air, which isn’t how supplemental oxygen works in practice.

The key idea is that the oxygen content of room air is about 21%. When you give supplemental oxygen, you increase the fraction of inspired oxygen, so the FiO2 rises above that 21% baseline. Therefore, the correct understanding is that supplemental oxygen raises FiO2 above 21%.

The other ideas don’t fit because room air already has its FiO2 at about 21%, so it wouldn’t be described as below that, and providing oxygen does not keep FiO2 at the exact same level. An exact value like 15% would be lower than ambient air, which isn’t how supplemental oxygen works in practice.