<unk>  <unk>  is the<unk>  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<unk> . Natural air includes 20.9% oxygen, which is equivalent to<unk>  of 0.21. Oxygen-enriched air has a higher<unk>  than 0.21, up to 1.00, which means 100% oxygen.<unk>  is typically maintained below 0.5 even with mechanical ventilation, to avoid oxygen toxicity.
Often used in medicine the<unk>  is used to represent the percentage of oxygen participating in gas-exchange.  If the barometric pressure changes, the<unk>  may remain constant while the partial pressure of oxygen changes with the change in barometric pressure.
Fraction of inspired oxygen
Pulse oximetry
Oxygen Enhancement Ratio
Respiratory rate
Arterial blood gas
Ventilation/perfusion ratio
Cardiothoracic ratio
Cardiac output