FiO2 equation: (flow rate in L/min x 4) + 20. What FiO2 would be predicted for 5 L/min?

FiO2 equation: (flow rate in L/min x 4) + 20. What FiO2 would be predicted for 5 L/min?

• A. 40%
• B. 60%
• C. 44%
• D. 20%

Answer: (A)

The key idea is that supplemental oxygen delivered through a nasal cannula raises the inspired oxygen in roughly 4 percentage points for every liter per minute of flow, starting from a room-air baseline. The given equation uses a simple approximation: FiO2 ≈ (flow in L/min × 4) + 20. Plugging in 5 L/min gives FiO2 ≈ (5 × 4) + 20 = 20 + 20 = 40%. So the predicted FiO2 is about 40%. Keep in mind this is an approximation used for standard nasal cannulas at modest flow; actual FiO2 can vary with cannula fit, patient breathing pattern, humidity, and whether higher-flow systems are used.

The key idea is that supplemental oxygen delivered through a nasal cannula raises the inspired oxygen in roughly 4 percentage points for every liter per minute of flow, starting from a room-air baseline. The given equation uses a simple approximation: FiO2 ≈ (flow in L/min × 4) + 20. Plugging in 5 L/min gives FiO2 ≈ (5 × 4) + 20 = 20 + 20 = 40%. So the predicted FiO2 is about 40%. Keep in mind this is an approximation used for standard nasal cannulas at modest flow; actual FiO2 can vary with cannula fit, patient breathing pattern, humidity, and whether higher-flow systems are used.