Blood circulation: Red =<unk> ated (arteries), Blue = deoxygenated (veins)<unk> is the fraction of<unk> -saturated hemoglobin relative to total hemoglobin (unsaturated + saturated) in the blood. The human body requires and regulates a very precise and specific balance of<unk>  in the blood. Normal arterial blood<unk> levels in humans are 95–100 percent. If the level is below 90 percent, it is considered low and called hypoxemia. Arterial blood<unk>  levels below 80 percent may compromise organ function, such as the brain and heart, and should be promptly addressed. Continued low<unk>  levels may lead to respiratory or cardiac arrest.<unk>  therapy may be used to assist in raising blood<unk>  levels.<unk> ation occurs when<unk>  molecules () enter the tissues of the body. For example, blood is<unk> ated in the lungs, where<unk>  molecules travel from the air and into the blood.<unk> ation is commonly used to refer to medical<unk>
Oxygen saturation 
Blood gas tension
Respiratory rate
Oxygenation index
Blood pressure
Fraction of inspired oxygen
Heart rate
Breathing gas