Arterial oxygen saturation, generally above 95%, is the percentage of the volume of oxygenated hemoglobin in the blood that is oxygenated to the total bound hemoglobin volume, i.e., the blood oxygen concentration, called arterial oxygen saturation, and is an important physiological parameter of the respiratory circulation. The ratio of saturation concentration to hemoglobin concentration is distinct from the percentage of oxygenated hemoglobin. Therefore, monitoring arterial oxygen saturation provides an estimate of the oxygenation of the lungs and the oxygen-carrying capacity of hemoglobin. Normal human arterial blood has an oxygen saturation of 95% or more, and venous blood is 75% or more.