A nasal cannula delivers oxygen at 1–6 L/min with approximately what percent inspired oxygen, depending on flow?

• A. 1-6 L/min; 24-44%.
• B. 10-15 L/min; 95%.
• C. 15-25 L/min; 60-80%.
• D. 2-4 L/min; 80-90%.

Answer: (A)

Oxygen concentration from a nasal cannula rises as you increase flow because the device delivers O2 into the nasal passages while ambient air is still being inhaled. At low flow, more room air dilutes the oxygen, giving a relatively modest FiO2. As flow increases toward 6 L/min, less air is drawn in and the inspired mixture becomes richer in oxygen, typically reaching about 44% at the high end. In practice, the exact FiO2 depends on how you breathe (mouth or nose), the fit of the cannula, and your tidal volume, so the range is a useful guide rather than an exact value. This is why nasal cannula at 1–6 L/min is described as delivering roughly 24–44% FiO2.