What is the typical oxygen concentration delivered by a bag-valve-mask (BVM) when connected to a high oxygen supply?

• A. Approximately 21%
• B. Approximately 35%
• C. Approximately 50%
• D. Nearly 100%

Answer: (D)

With a bag-valve-mask attached to a high-flow oxygen source and a good mask seal, you can deliver oxygen concentrations that are essentially 100%. The reservoir bag fills with oxygen, and when you squeeze the bag or the patient inspires, the charted gas that reaches the lungs is drawn largely from that oxygen-rich reservoir rather than ambient air. A tight seal minimizes entrainment of room air, and the high oxygen flow keeps the reservoir filled between breaths, pushing the inspired gas toward pure oxygen. In real-world use a perfect 100% FiO2 isn’t guaranteed due to leaks or imperfect technique, but “nearly 100%” is the typical expectation with proper setup.