Fraction of inspired oxygen

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 FIO2. Natural air includes 21% oxygen, which is equivalent to FIO2 of 0.21. Oxygen-enriched air has a higher FIO2 than 0.21; up to 1.00 which means 100% oxygen. FIO2 is typically maintained below 0.5 even with mechanical ventilation, to avoid oxygen toxicity,[2] but there are applications when up to 100% is routinely used.

Often used in medicine, the FIO2 is used to represent the percentage of oxygen participating in gas-exchange. If the barometric pressure changes, the FIO2 may remain constant while the partial pressure of oxygen changes with the change in barometric pressure.

  1. ^ Wagner, Peter D. (2021-03-01). "i stands for internet (and other things), not for inspired O 2 concentration". American Journal of Physiology. Lung Cellular and Molecular Physiology. 320 (3): L467. doi:10.1152/ajplung.00610.2020. ISSN 1040-0605. PMID 33750222.
  2. ^ Bitterman H (2009). "Bench-to-bedside review: oxygen as a drug". Crit Care. 13 (1): 205. doi:10.1186/cc7151. PMC 2688103. PMID 19291278.