Which device can deliver high concentrations of oxygen, typically 80–100%, at 12–15 L/min?

• A. Nonrebreather mask (NRB)
• B. Nasal cannula
• C. Simple face mask
• D. Bag-valve mask

Answer: (A)

Delivering the highest oxygen concentration to a patient who is breathing on their own relies on a device with a reservoir and one-way valves that prevent room air from diluting the oxygen. The nonrebreather mask does this best. It has a reservoir bag that fills with oxygen and valves that stop exhaled gas from mixing back in. When you run oxygen at about 12–15 L/min and seal the mask well, the patient inhales mostly oxygen from the bag, giving an FiO2 around 80–100%.

The other options don’t maintain that high concentration as reliably. A nasal cannula delivers oxygen through the nostrils at lower flows, topping out around 44–50% FiO2. A simple face mask without a reservoir tends to deliver roughly 40–60% FiO2 at 6–10 L/min and can be compromised by leaks or mouth breathing. A bag-valve mask can deliver very high FiO2, but it’s a manual ventilation device used to assist breathing, not a fixed device for a spontaneously breathing patient; its high FiO2 depends on active ventilation and the operator, not just the device itself.