Which device is capable of delivering up to 100% FiO₂ at high flow rates?

• A. Non-rebreather mask
• B. Nasal cannula
• C. Simple face mask
• D. Partial rebreather mask

Answer: (A)

The ability to deliver the highest possible FiO2 depends on having a reservoir of oxygen and a way to prevent rebreathing of exhaled air. The non-rebreather mask uses a reservoir bag filled with oxygen and one-way valves that close during inhalation, so most of what’s inhaled comes from the oxygen in the bag rather than room air. Exhaled air exits through side vents, not back into the bag, allowing near 100% FiO2 when the flow is high enough to keep the bag inflated.

Nasal cannula delivers oxygen without a reservoir, so inhaled air is mixed with room air, typically capping FiO2 around the lower range (often up to the mid-40s at higher flows). A simple face mask covers the nose and mouth but leaks around the edges and also has no reservoir, limiting FiO2 to roughly the mid-30s to about 50%. A partial rebreather mask has a reservoir but lacks the full one-way valve system, so some exhaled air re-enters the mix, usually achieving up to about 60–70% FiO2 depending on flow.

Thus, the non-rebreather mask is capable of delivering up to 100% FiO2 at high flow rates when the bag stays inflated and the valves function properly.