Which device does not follow the FiO2 equation for estimating FiO2?

Which device does not follow the FiO2 equation for estimating FiO2?

• A. Nasal cannula
• B. Venturi mask
• C. Simple mask
• D. Oxymizer

Answer: (D)

The main idea is that the simple FiO2 estimation you learn for common oxygen devices assumes a straightforward relationship between how much oxygen you flow into the system and how much ends up in the lungs. For devices like a nasal cannula or a simple oxygen mask, the delivered FiO2 tends to follow that rough flow-based pattern because there isn’t a stored reservoir inside delivering oxygen on top of the flow. The oxymizer is different: it has a reservoir that stores oxygen and releases it during inspiration. That stored oxygen augments what reaches the lungs beyond what the continuous flow alone would deliver, so the actual FiO2 can be higher—and not reliably predicted by the simple flow-to-FiO2 equation. In other words, you can’t rely on the straightforward FiO2 = ambient 21% + (flow × 0.04) for this device because its performance depends on the reservoir and the patient’s inspiratory effort. Nasal cannula and simple masks generally conform more closely to that rough equation, while devices like venturi masks provide a fixed FiO2 by design (their delivered oxygen is set by the adapter, not by a simple flow-based calculation). The reservoir-based oxymizer breaks the simple relationship, which is why it’s the correct choice here.

The main idea is that the simple FiO2 estimation you learn for common oxygen devices assumes a straightforward relationship between how much oxygen you flow into the system and how much ends up in the lungs. For devices like a nasal cannula or a simple oxygen mask, the delivered FiO2 tends to follow that rough flow-based pattern because there isn’t a stored reservoir inside delivering oxygen on top of the flow.

The oxymizer is different: it has a reservoir that stores oxygen and releases it during inspiration. That stored oxygen augments what reaches the lungs beyond what the continuous flow alone would deliver, so the actual FiO2 can be higher—and not reliably predicted by the simple flow-to-FiO2 equation. In other words, you can’t rely on the straightforward FiO2 = ambient 21% + (flow × 0.04) for this device because its performance depends on the reservoir and the patient’s inspiratory effort.

Nasal cannula and simple masks generally conform more closely to that rough equation, while devices like venturi masks provide a fixed FiO2 by design (their delivered oxygen is set by the adapter, not by a simple flow-based calculation). The reservoir-based oxymizer breaks the simple relationship, which is why it’s the correct choice here.