The<unk>  is used in the APACHE II (Acute Physiology and Chronic Health Evaluation II) severity of disease classification system for intensive care unit patients. For<unk>  values equal to or greater than 0.5, the alveolar–arterial gradient value should be used in the APACHE II score calculation. Otherwise, the PaO2 will suffice. The ratio between partial pressure of oxygen in arterial blood (PaO2) and<unk>  is used as an indicator of hypoxemia per the American-European Consensus Conference on lung injury. A high<unk>  has been shown to alter the ratio of PaO2/FIO2.
Fraction of inspired oxygen
Oxygen saturation 
Oxygen saturation
Minute ventilation
Oxygenation index
Pulse oximetry
Mandatory minute ventilation
Respiratory rate