At 2 L/min via nasal cannula, what is the approximate FiO2 delivered?

• A. About 60–70%.
• B. About 15–20%.
• C. About 28–32% (commonly cited around 28%).
• D. About 0%.

Answer: (C)

FiO2 from a nasal cannula rises with flow, but the device is a low-flow system and can’t deliver very high oxygen concentrations. Room air is about 21% O2, and with a standard nasal cannula, each liter per minute adds roughly 4% to the FiO2. At 2 L/min, that gives about 21% + (2 × 4%) ≈ 29%, which falls in the 28–32% range. In reality, the exact value varies with how the patient is breathing and how well the cannula fits. Higher FiO2 (around 60–70%) is typically delivered by devices like a nonrebreather mask, not a nasal cannula. So the best approximation at 2 L/min is about 28–32%.