Which statement about oxygen delivery devices is true, specifically regarding nonrebreather masks?

• A. They deliver the lowest FiO2 among standard devices.
• B. They do not require humidification.
• C. They require 10-15 L/min flow and provide the highest FiO2 among standard devices.
• D. They are used for low oxygen needs.

Answer: (C)

Nonrebreather masks provide the highest oxygen concentration among standard delivery devices because the mask has a reservoir that is filled with oxygen and one-way valves that prevent inhaled air from mixing with exhaled air. This design keeps the inspired gas rich in oxygen, so the device can deliver a very high FiO2 when used correctly. To maintain that high FiO2, a high flow rate is needed—typically 10–15 L/min—to keep the reservoir inflated during inspiration. If the flow is too low, the bag deflates and the patient ends up breathing more exhaled air, reducing the FiO2. These masks are chosen for patients with significant oxygen needs, not for low oxygen requirements. Humidification is not a defining requirement for this device; it’s not strictly necessary, though it may be used in some situations to improve comfort.