Which device delivers the highest oxygen concentration among the listed options during non-urgent care?

• A. Nasal Cannula
• B. Simple Mask
• C. Nonrebreather Mask
• D. Bag-Valve Mask

Answer: (C)

The device that can deliver the highest oxygen concentration to a spontaneously breathing patient is the one with a reservoir and one-way valves to prevent mixing with exhaled air. The nonrebreather mask uses a reservoir bag and valves so exhaled gas doesn’t dilute the inhaled oxygen, allowing you to achieve very high FiO2—typically around 90% or more with proper flow. In contrast, a nasal cannula provides up to about 40–44% O2, and a simple mask roughly 40–60%. A bag-valve mask can deliver near‑100% oxygen as well, but it is primarily a ventilation device used for active ventilations rather than continuous non-urgent oxygen therapy. So, in this non-urgent care context, the nonrebreather mask delivers the highest oxygen concentration.