The<unk>  is a calculation used in intensive care medicine to measure the fraction of inspired oxygen (FiO2) and its usage within the body. A lower<unk>  is better - this can be inferred by the equation itself. As the<unk>  of a person improves, they will be able to achieve a higher PaO2 at a lower FiO2. This would be reflected on the formula as a decrease in the numerator or an increase in the denominator - thus lowering the<unk> . Typically an<unk>  threshold is set for when a neonate should be placed on ECMO, for example >40.
Oxygenation index
Oxygen saturation 
Oxygen saturation
Oxygen enhancement ratio
Fraction of inspired oxygen
Arteriovenous oxygen difference
Pulse oximetry
NC ratio