What does the term "fraction of inspired oxygen" (FiO2) refer to?

The term "fraction of inspired oxygen" (FiO2) specifically refers to the percentage of oxygen present in the air that a person inhales. In atmospheric air, the FiO2 is typically around 21% at sea level, which means that in the inspired air, approximately 21% of the gas is oxygen. This concept is crucial for understanding how much oxygen a patient is receiving, especially in clinical settings where supplemental oxygen is involved.

By knowing the FiO2, healthcare providers can assess and manage the patient's oxygenation needs effectively. For patients receiving supplemental oxygen, the FiO2 can be adjusted based on the delivery method, such as nasal cannulas or masks, which helps ensure they receive sufficient oxygen to meet their physiological requirements.