SaO2 in medical terms is arterial oxygen saturation, S stands for ratio, a stands for artery, and O2 is the molecular formula for oxygen. Arterial oxygen saturation refers to the hemoglobin bound to oxygen in arterial blood, as a percentage of all hemoglobin, with a normal range of 95%-98%. Because there is sufficient oxygen in the arteries, most of the hemoglobin is bound to oxygen and the arterial oxygen saturation is relatively high. If the arterial oxygen saturation is above the normal range, it commonly occurs after hyperbaric oxygen therapy. If the oxygen saturation is below normal, the most common is a problem with pulmonary ventilation function and or gas exchange function, common diseases are chronic bronchitis, bronchial asthma; diseases with pulmonary gas exchange function, common is pulmonary fibrosis.