<unk>  is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood.<unk>  has many causes, and often causes hypoxia as the blood is not supplying enough oxygen to the tissues of the body.
Hypoxemia
Hypercapnia
Hypocapnia
Hyperaemia
Hypoventilation
Acidosis
Hypothermia
Hyperoxia