The fraction of inspired oxygen (FiO2) is the concentration of oxygen in the gas mixture. The gas mixture at room air has a fraction of inspired oxygen of 21%, meaning that the concentration of oxygen at room air is 21%.

Fraction of inspired oxygen (FiO2) is the percentage or concentration of oxygen in the air mixture that a person inhales. Under normal atmospheric conditions, the FiO2 is approximately 21%, as this is the oxygen concentration in room air.

In medical settings, the fraction of inspired oxygen (FiO2) plays a critical role in determining the concentration of oxygen delivered to a patient. It is a fundamental parameter that healthcare professionals monitor and adjust to ensure adequate oxygenation.

Fraction of inspired oxygen (FIO2), correctly denoted with a capital I, [1] is the molar or volumetric fraction of oxygen in the inhaled gas. Medical patients experiencing difficulty breathing are provided with oxygen-enriched air, which means a higher-than-atmospheric FI O 2.