Using the FiO2 equation, what FiO2 would be predicted for 4 L/min?

Using the FiO2 equation, what FiO2 would be predicted for 4 L/min?

• A. 32%
• B. 34%
• C. 36%
• D. 44%

Answer: (C)

The main idea is how FiO2 rises with nasal cannula flow. A common rule is FiO2 ≈ 21% plus about 4% for each additional liter per minute of O2 delivered. So at 4 L/min, that gives about 21% + (4 × 4%) = 37%. In practice this is typically rounded to around 36%–37%, so the closest option is 36%. The other numbers don’t line up with the 4% per liter rule for 4 L/min, either being too low or too high for this flow. Remember that the actual FiO2 can vary with breathing pattern and how well the cannula fits, but the 36% estimate fits the standard approximation for 4 L/min.

The main idea is how FiO2 rises with nasal cannula flow. A common rule is FiO2 ≈ 21% plus about 4% for each additional liter per minute of O2 delivered. So at 4 L/min, that gives about 21% + (4 × 4%) = 37%. In practice this is typically rounded to around 36%–37%, so the closest option is 36%. The other numbers don’t line up with the 4% per liter rule for 4 L/min, either being too low or too high for this flow. Remember that the actual FiO2 can vary with breathing pattern and how well the cannula fits, but the 36% estimate fits the standard approximation for 4 L/min.