Are simple facemask and nasal cannula open systems?

• A. Sometimes
• B. No
• C. Only when used with extra oxygen
• D. Yes

Answer: (D)

Open systems are oxygen delivery methods that do not form a sealed breathing circuit. With these devices, the patient’s breath mixes with room air and exhaled gas exits to the surroundings, not into a closed reservoir.

A simple facemask and a nasal cannula fit this description. The nasal cannula delivers oxygen through prongs into the nostrils while the rest of the breath comes from room air; the facemask covers the nose and mouth but does not seal tightly, so air leaks around the edges and ambient air mixes in. Because there’s no closed loop or reservoir that traps air, these devices are considered open systems. This is why they don’t provide a controlled, positive-pressure, closed breathing circuit, and their delivered oxygen concentration is influenced by how the patient breathes and how well the device fits.