Which device delivers 100% oxygen concentration in typical EMS use?

• A. Nasal Cannula
• B. Non-Rebreather Mask
• C. Simple Face Mask
• D. Bag Valve Mask

Answer: (D)

Delivering the highest oxygen concentration depends on having a reservoir and a seal so that oxygen isn’t diluted by room air. A bag-valve-mask combines a tight-sealing face mask, the Ambu bag, and an oxygen reservoir. When you squeeze the bag and keep a good seal, the patient inhales gas drawn from the reservoir with each breath, giving near–100% oxygen concentration during ventilation.

Nasal cannulas feed oxygen passively through the nose and mix with room air, so the inspired fraction is relatively low—roughly in the 24–44% range depending on flow. A simple face mask improves on that but still typically provides only about 40–60% oxygen, influenced by fit and flow. A non-rebreather mask can reach very high concentrations if the reservoir stays full and the mask fits well, but it relies on the patient’s breathing and conditions that can allow dilution, so it’s not as reliably close to 100% as a properly used bag-valve-mask during active ventilation.

So, in typical EMS use, the device that delivers effectively the highest oxygen concentration is the bag-valve-mask.