What is the typical oxygen concentration delivered by a nasal cannula at its maximum flow?

• A. Up to about 44% O2 at 6 L/min.
• B. 100% O2 at 6 L/min.
• C. 20% O2 at 6 L/min.
• D. 60% O2 at 6 L/min.

Answer: (D)

The main idea is that a nasal cannula can raise the oxygen level a patient breathes, but only to a limited extent because ambient air mixes with the oxygen being delivered. At the highest practical flow with a nasal cannula (about 6 L/min), you can typically achieve around 40–44% O2. In other words, it’s not possible to reach 60% or 100% O2 with this device alone. To deliver higher FiO2, you’d use a different interface such as a mask (e.g., nonrebreather or Venturi) that minimizes room-air entrainment. So the best choice reflects that maximum around 44% O2 at 6 L/min.