FiO2 stands for Fraction of Inspired Oxygen, which is the concentration of oxygen in the gas mixture that a person inhales and is involved in gas exchange at the alveolar level. The gas mixture at room air has a FiO2 of 21%, meaning that the concentration of oxygen at room air is 21%. Understanding oxygen delivery and interpreting FiO2 values are imperative for the proper treatment of hypoxemia, especially in critically ill patients
. Different oxygen delivery devices deliver to the patient more or less of a percentage of what is coming in from the tank, and the FiO2 for each device varies
