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Fraction of inspired oxygen (''Fi''O2) is the fraction or percentage of oxygen in the space being measured. Medical patients experiencing difficulty breathing are provided with oxygen-enriched air, which means a higher-than-atmospheric ''Fi''O2. Natural air includes 20.9% oxygen, which is equivalent to ''Fi''O2 of 0.209. Oxygen-enriched air has a higher ''Fi''O2 than 0.21, up to 1.00, which means 100% oxygen. ''Fi''O2 is typically maintained below 0.5 even with mechanical ventilation, to avoid oxygen toxicity.〔http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2688103/〕 If a patient is wearing a nasal cannula or a simple face mask, each additional liter of oxygen adds about 4% to their FiO2 (for example, a patient with a nasal cannula with 2L of oxygen attached would have an FIO2 of 21% + 8% =29%). Often used in medicine the ''Fi''O2 is used to represent the percentage of oxygen participating in gas-exchange. If the barometric pressure changes, the ''Fi''O2 may remain constant while the partial pressure of oxygen changes with the change in barometric pressure. == Equations == ;Abbreviated alveolar air equation :: PAO2, PEO2, and PiO2 are the partial pressures of oxygen in alveolar, expired, and inspired gas, respectively, and VD/VT is the ratio of physiologic dead space over tidal volume. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Fraction of inspired oxygen」の詳細全文を読む スポンサード リンク
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