In healthy adults the normal PO2 is 80-100 mmHg .
Hypoxemia can be defined as diminished amount of oxygen in the arterial blood, shown by decreased partial pressure of oxygen (PO2) and reduced saturation in arterial blood sample .
PO2 values less than 80 mmHg is considered hypoxemia, however, with advancing age the ability of the lungs to exchange the blood declines progressively, the PO2 is decreased by one mmHg for each year above 60.
For example a 70 years old male, will not be considered hypoxemic unless the PO2 is less than 71mmHg.
according to arterial sample PO2 the severity of hypoxemia can divided into 3 main forms
Mild hypoxemia : PO2 60-79 mmHg
Moderate hypoxemia : PO2 40-59 mmHg
Severe hypoxemia : PO2 < 40 mmHg
The PaO2/FiO2 ratio in another common measure of oxygenation.
A normal PaO2/FiO2 ratio is 300 to 500 mmHg, with values less than 300 mmHg indicating abnormal gas exchange and values less than 200 mmHg indicates severe hypoxemia .