The FiO2 equation does NOT work for which device?

The FiO2 equation does NOT work for which device?

• A. Nasal cannula
• B. Venturi mask
• C. Non-rebreather mask
• D. Oxymizer

Answer: (D)

The key idea is that some oxygen delivery devices rely on a reservoir, not just a constant flow, to determine how much oxygen reaches the patient. The usual FiO2 estimate works reasonably well for devices that mix oxygen with room air in a straightforward, continuous flow—like nasal cannulas or simple masks—because FiO2 becomes a relatively predictable function of the prescribed flow. But the Oxymizer uses a built-in reservoir that stores oxygen and releases it during inspiration. Because of that reservoir, the actual FiO2 delivered depends on how much oxygen is stored, the patient’s breathing pattern (tidal volume and inspiratory flow), and the timing of inspiration, not simply the flow rate. In other words, the simple FiO2 equation breaks down for this device because it cannot accurately account for how oxygen is delivered from the reservoir during the breathing cycle. So, the FiO2 equation does not reliably apply to the Oxymizer.

The key idea is that some oxygen delivery devices rely on a reservoir, not just a constant flow, to determine how much oxygen reaches the patient. The usual FiO2 estimate works reasonably well for devices that mix oxygen with room air in a straightforward, continuous flow—like nasal cannulas or simple masks—because FiO2 becomes a relatively predictable function of the prescribed flow.

But the Oxymizer uses a built-in reservoir that stores oxygen and releases it during inspiration. Because of that reservoir, the actual FiO2 delivered depends on how much oxygen is stored, the patient’s breathing pattern (tidal volume and inspiratory flow), and the timing of inspiration, not simply the flow rate. In other words, the simple FiO2 equation breaks down for this device because it cannot accurately account for how oxygen is delivered from the reservoir during the breathing cycle.

So, the FiO2 equation does not reliably apply to the Oxymizer.