FiO2, in the field of medicine,'s the fraction of inspired oxygen in a gas mixture. The FiO2's expressed as a number from 0 (0%) to 1 (100%). The FiO2 of normal room air's 0.21 (21%). A patient's FiO2 may be varied through the use of different Venturi masks, in combination with varying oxygen flow rates. In addition, most mechanical ventilators have controls for adjusting FiO2. An increased FiO2's necessary in managing adequate oxygenation in patients who're critically ill due to causes such as… (More on Fio2)