Blood oxygen is the percentage of oxygen bound to hemoglobin in the blood as a percentage of all oxygen. The blood pressure range for a normal person is between 95% and 100%. If the blood oxygen is around 90%, the patient will have mild hypoxic symptoms and will feel chest tightness and shortness of breath. At this time, if the patient is kept quiet and given oxygen, the patient’s symptoms can usually be reduced. If the blood oxygen is below 80%, the patient will have obvious symptoms of hypoxia and feel chest tightness, shortness of breath and difficulty in breathing. Even if high flow oxygen is given, the patient will feel no significant improvement in the symptoms of chest tightness, which is more dangerous at this time. This condition is common in various respiratory system diseases and circulatory system diseases, such as severe pneumonia, pulmonary fibrosis, etc. If the oxygen saturation is below 50%, it is often a sign of advanced disease, signaling that the patient’s respiratory function is about to fail. The patient’s general condition is often characterized by severe dyspnea, profuse facial sweating, cyanosis of the lips, and a large number of wet rales can be heard in both lungs. At this time, it is difficult to relieve the patient’s symptoms even with various diuretic and oxygen treatments.