How does oxygen differ from air in terms of FiO2?

How does oxygen differ from air in terms of FiO2?

• A. Ambient air contains about 21% oxygen; supplemental oxygen increases FiO2 above 21%.
• B. Ambient air contains about 50% oxygen.
• C. Ambient air has no oxygen.
• D. Oxygen therapy decreases FiO2.

Answer: (A)

FiO2 is the fraction of inspired oxygen. Room air contains about 21% oxygen, so FiO2 is around 0.21. Delivering supplemental oxygen raises the amount of oxygen the patient breathes, pushing FiO2 above that baseline. The exact level depends on the device and flow, from modest increases with a nasal cannula to nearly 100% with certain masks or ventilators. So oxygen therapy increases FiO2 rather than decreasing it, which is why the statement about ambient air being 21% and supplemental oxygen raising FiO2 is correct.

FiO2 is the fraction of inspired oxygen. Room air contains about 21% oxygen, so FiO2 is around 0.21. Delivering supplemental oxygen raises the amount of oxygen the patient breathes, pushing FiO2 above that baseline. The exact level depends on the device and flow, from modest increases with a nasal cannula to nearly 100% with certain masks or ventilators. So oxygen therapy increases FiO2 rather than decreasing it, which is why the statement about ambient air being 21% and supplemental oxygen raising FiO2 is correct.