Which oxygen delivery device provides the highest FiO2 when used properly?

• A. Nasal cannula
• B. Simple face mask
• C. Nonrebreather mask
• D. Venturi mask

Answer: (C)

The device that delivers the highest FiO2 when used correctly relies on having a reservoir of oxygen and a design that minimizes mixing with room air. The nonrebreather mask uses a reservoir bag and one-way valves so during inhalation the patient mainly draws oxygen from the bag, not from surrounding air, and exhaled air exits through separate ports rather than back into the bag. When the flow is high enough to keep the bag full, the inhaled gas is almost pure oxygen, approaching 100% FiO2.

In contrast, a nasal cannula provides oxygen through a small tube in the nostrils and always mixes with room air in the lungs, yielding about 24–44% FiO2 depending on flow. A simple face mask allows more room-air entrainment around the edges and typically delivers roughly 40–60% FiO2, depending on flow. A Venturi mask can deliver precise, known FiO2 using adapters, but its maximum FiO2 is generally less than what a well-used nonrebreather can provide.

To achieve the highest FiO2, keep the reservoir bag inflated with an adequate flow (often around 10–15 L/min) and ensure a good seal so there’s minimal dilution with room air.