Which statement is true regarding the flow rate for a nonrebreathing mask?

• A. 3 L/min.
• B. 6 L/min.
• C. 12 L/min.
• D. 15 L/min.

Answer: (B)

The idea being tested is keeping the breathing circuit of a nonrebreathing mask free from rebreathing by delivering enough fresh gas flow to keep the reservoir bag inflated.

A nonrebreathing mask uses a reservoir bag and one-way valves so the patient mostly breathes from the bag and from the incoming oxygen, while exhaled gas exits through the mask’s vents. To prevent the bag from collapsing and to flush CO2 out of the system, there must be a minimum amount of flow that exceeds the patient’s inspiratory demand. That minimum is about 6 L/min. If the flow falls below this, the bag can deflate during inhalation, and the patient may end up drawing in exhaled gas, defeating the purpose of the mask.

Higher flows, such as around 10–15 L/min, are common in practice to ensure the FiO2 stays high and the bag remains well inflated, but the essential true statement about the flow rate is that a minimum of roughly 6 L/min is required to prevent rebreathing.