A reservoir mask with CLOSED exhalation ports indicates which mask type?

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

Answer: (D)

The key idea is how the mask’s reservoir and exhalation valves control rebreathing and oxygen concentration. In a non-rebreather setup, the reservoir bag fills with oxygen from the source, and the exhalation ports are equipped with one-way valves so that exhaled air leaves through those ports instead of entering the reservoir. This prevents rebreathing exhaled gas and ensures that the inhaled gas comes primarily from fresh oxygen in the reservoir, delivering a high fraction of inspired oxygen when the flow is appropriate.

If the mask had open exhalation ports and no proper valves to keep exhaled air out of the reservoir, some of the exhaled gas could mix with the inhaled gas, lowering the FiO2. That’s what happens with a simple mask, which lacks a reservoir and tends to deliver a lower, more variable oxygen concentration. A nasal cannula also provides oxygen but without a reservoir and without the ability to achieve the high FiO2 associated with a non-rebreather. A partial rebreather has a reservoir but with ports that allow some exhaled air to re-enter the reservoir, giving an intermediate FiO2—not as high as a true non-rebreather.