Which oxygen delivery device provides the highest oxygen concentration when used appropriately?

• A. Nasal Cannula
• B. Venturi Mask
• C. Non-Rebreather
• D. Simple Face Mask

Answer: (C)

The highest oxygen concentration is achieved with a mask that uses a reservoir and one-way valves to prevent dilution with room air. When the reservoir bag is filled with oxygen and the flow is set high enough, inhalation pulls from that oxygen-rich reservoir while exhaled air exits through the side ports, so the inspired gas can approach nearly 100% oxygen. If the bag collapses or the flow is too low, the FiO2 falls because room air mixes in. This makes the non-rebreather mask the best option for delivering the greatest O2 concentration when used correctly.

In comparison, a venturi mask provides a precise but typically lower and fixed range of FiO2 (often up to about 60%), a nasal cannula delivers roughly 24–44% depending on flow, and a simple face mask delivers around 40–60% without a dedicated reservoir.