How is the FIO2 calculated using the flow rate?

The calculation of FIO2 (Fraction of Inspired Oxygen) using the flow rate involves understanding how supplemental oxygen affects the concentration of oxygen delivered to a patient. When a patient is receiving supplemental oxygen via a high-flow system, the amount of oxygen they inhale is influenced by the flow rate of the oxygen mixed with room air.

The correct method to estimate FIO2 when using a nasal cannula or similar device is to take the flow rate in liters per minute and multiply it by 4, then add a baseline of 20%. This is based on the fact that room air contains approximately 21% oxygen. As the flow rate increases, the proportion of oxygen delivered increases above the ambient level.

In this context, the calculation can be summarized as follows: For every liter of oxygen flow, the FIO2 increases by approximately 4% due to the dilution of room air with supplemental oxygen. Therefore, if you have a flow rate of, for example, 2 L/min, the calculation would be (2 x 4) + 20 = 28% FIO2. This method allows healthcare providers to quickly estimate the percentage of oxygen the patient is receiving based on the flow rate.

This understanding is particularly important in clinical practice to