Non-rebreather mask has FiO2 of what range on a flow rate of about 0.9 L/min?

• A. 0.60-0.80+, 0.9 L/min
• B. 0.21-0.30, 2-3 L/min
• C. 0.95-1.00, 8-10 L/min
• D. 0.40-0.60, 6-8 L/min

Answer: (A)

The key idea is how oxygen delivery devices depend on flow to maintain a high concentration in the inhaled air. A non-rebreather mask uses a reservoir bag and one-way valves to limit mixing with room air and to keep the inhaled oxygen rich. But the actual FiO2 you get depends on whether the reservoir bag stays inflated during each breath. When the flow is only about 0.9 L/min, that flow is usually insufficient to keep the bag full for the patient’s entire inspiration, so some room air is drawn in as well. That dilutes the oxygen, giving a moderate FiO2, typically around 0.60 to 0.80. Only with substantially higher flows (roughly 8–15 L/min) does the bag stay inflated enough to push FiO2 up toward 0.95–1.00, which is the scenario most people associate with a non-rebreather.

So, at a low-ish flow like 0.9 L/min, the non-rebreather tends to deliver FiO2 in the 0.60–0.80 range rather than the very high end.