SAO2 is the abbreviation for arterial oxygen saturation, which is the ratio of oxyhemoglobin to all hemoglobin in the body in arterial blood. The normal human arterial oxygen saturation is 98% or higher. Clinical monitoring of arterial oxygen saturation provides a quantitative assessment of the oxygen-carrying capacity of oxygenated hemoglobin in both lungs and the ability to transport oxygen, primarily to clarify the ability of the blood to carry and transport oxygen. Oxygen usually enters the human blood through the respiratory system and then combines with the hemoglobin of the red blood cells in the blood to become oxyhemoglobin, an indicator measured by the arterial oxygen saturation. If there is a lack of oxygen in the body, the oxygen saturation level will decrease. If the arterial oxygen saturation is less than 94%, the oxygen supply to the body is insufficient, resulting in hypoxemia.