Hypoxemia is generally a severe ventilation or gas exchange dysfunction, resulting in a decrease in arterial partial pressure of oxygen as well as blood oxygen saturation, and the patient presents with clinical manifestations such as dyspnea, cyanosis, and shortness of breath. Common causes may include airway obstructive lesions, lung tissue lesions, neuromuscular diseases and so on. 1. Obstructive airway lesions: if the patient has chronic non-obstructive diseases, asthma and other diseases, it may cause airway spasm, inflammatory edema, resulting in the diameter of the airway lumen becoming smaller, thus affecting pulmonary ventilation and hypoxemia. 2. Lung tissue lesions: lung tissue lesions are commonly pneumonia, emphysema, tuberculosis, pulmonary fibrosis, pulmonary edema, etc. The above diseases will affect gas exchange to different degrees, and when the exchanged oxygen can not satisfy the body, it will cause hypoxemia. 3. Neuromuscular diseases: when patients have cerebrovascular diseases, such as cerebral infarction, or encephalitis, craniocerebral trauma, various types of drug poisoning. The above causes will lead to the respiratory muscles can not work normally, so that the lung ventilation is reduced, thus causing hypoxemia. The causes of hypoxemia are many and the etiology is relatively complex, so it is recommended to consult a doctor in time and choose the appropriate treatment according to the etiology.