Which reservoir mask delivers the highest possible O2 via mask?

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

Answer: (C)

The amount of oxygen a mask delivers depends on how much room air dilutes the inspired gas. A reservoir mask stores oxygen in a bag, but the key difference is how the device handles exhaled air. The non-rebreather has a one-way valve and a tight seal that prevents room air from entering the reservoir during inspiration and keeps exhaled air out of the bag. This design means the person is breathing mostly pure oxygen from the reservoir, so the inspired oxygen concentration can be the highest among standard mask systems when the flow is adequate and the bag stays inflated.

In contrast, the partial rebreather also uses a reservoir but lacks a valve that blocks inhaled air from mixing with exhaled gas. Some of the exhaled gas can re-enter the reservoir, diluting the oxygen with non-oxygen components and lowering the FiO2. Simple masks don’t have a true reservoir, so they mix room air with delivered oxygen, resulting in a lower and more variable FiO2. A nasal cannula isn’t a reservoir mask at all, and its maximum oxygen concentration is limited and usually lower than what a non-rebreather can deliver.

So, the non-rebreather mask delivers the highest possible oxygen concentration via mask when used with sufficient flow and a properly inflated reservoir.