Which variable decreases the FIO2 in low-flow oxygen systems?

In low-flow oxygen systems, the fraction of inspired oxygen (FIO2) is influenced primarily by the inspiratory flow rate. When there is a high inspiratory flow, it can lead to a dilution effect as the patient breathes in ambient air along with the supplemental oxygen. This occurs because low-flow oxygen systems do not have a mechanism to deliver a consistent, high concentration of oxygen; instead, they rely on the patient drawing in air from the environment. Therefore, with a high inspiratory flow, the percentage of oxygen in the air mixture decreases, resulting in a lower FIO2.

The understanding of how FIO2 varies with different flow rates highlights the importance of matching oxygen delivery to patient needs, especially in clinical settings. In contrast, other variables like low tidal volume or low inspiratory flow do not have the same effect on FIO2 reduction as high inspiratory flow does; they can either maintain or slightly change the FIO2, depending on the system in use and the patient’s condition.