The nonrebreathing mask delivers up to ______% inspired oxygen when a good seal is maintained and a 15 L/min flow.

• A. 70
• B. 100
• C. 90
• D. 80

Answer: (C)

A nonrebreathing mask delivers a very high inspired oxygen concentration when the mask fits well and the flow is set high, because the reservoir holds oxygen and the one-way valves prevent room air from diluting it. With a good seal and about 15 L/min, the inspired oxygen concentration is typically around ninety percent. It isn’t guaranteed to reach one hundred percent because a small amount of ambient air can still be entrained during inhalation and any leaks or a deflating reservoir will dilute the mix. So the best answer is about ninety percent. To maintain that level, keep the mask snug, ensure the reservoir bag remains partially inflated, and maintain the recommended flow.