What is the maximum FIO2 that can be delivered by a nasal cannula?

What is the maximum FIO2 that can be delivered by a nasal cannula?

• A. 0.25
• B. 0.30
• C. 0.40
• D. 0.45

Answer: (D)

The main idea is that a nasal cannula delivers oxygen by mixing it with room air as the patient inhales, so the FiO2 increases with higher flow but cannot be pushed arbitrarily high because ambient air keeps diluting the mix. In practice, the delivered FiO2 with a nasal cannula tops out around the mid-40s percent. At the highest commonly used flow (about 6 L/min), you typically achieve roughly 44–45% FiO2. That’s why the maximum FiO2 associated with a nasal cannula is about 0.45. Lower values (0.25, 0.30, 0.40) occur at lower flows or with factors like mouth breathing, but they don’t reflect the ceiling of what a nasal cannula can deliver.

The main idea is that a nasal cannula delivers oxygen by mixing it with room air as the patient inhales, so the FiO2 increases with higher flow but cannot be pushed arbitrarily high because ambient air keeps diluting the mix. In practice, the delivered FiO2 with a nasal cannula tops out around the mid-40s percent. At the highest commonly used flow (about 6 L/min), you typically achieve roughly 44–45% FiO2. That’s why the maximum FiO2 associated with a nasal cannula is about 0.45. Lower values (0.25, 0.30, 0.40) occur at lower flows or with factors like mouth breathing, but they don’t reflect the ceiling of what a nasal cannula can deliver.