Which oxygen delivery device is capable of delivering up to 90% inspired oxygen with a tight seal at high flow?

• A. Oxygen tent
• B. Nasal cannula
• C. Simple face mask
• D. Nonrebreathing mask

Answer: (D)

The key idea is delivering a high concentration of oxygen by preventing air from diluting the inhaled gas. A nonrebreathing mask uses a reservoir bag and one-way valves on the exhalation ports, so during inhalation the mask draws mostly oxygen from the bag and the oxygen source rather than room air. When it’s fitted tightly and supplied with high flow (typically about 10–15 L/min), the bag stays inflated and the valves limit entrainment, allowing inspired oxygen concentrations to approach about 90%.

Nasal cannulas deliver relatively low FiO2 because they primarily add oxygen to the air the patient is already drawing in and don’t prevent room-air entrainment. Simple face masks provide a modest increase but are limited by leaks and inability to maintain a high, constant FiO2. Oxygen tents are not a tight-seal delivery and aren’t suitable for achieving very high FiO2 quickly. So the nonrebreathing mask is the device capable of delivering up to near 90% inspired oxygen with a tight seal at high flow.