The normal arterial blood oxygen level is 80-100 mmHg. If the partial pressure of oxygen is 60-80 mmHg, the patient has mild hypoxemia; if the partial pressure of oxygen is 40-60 mmHg, the patient has moderate hypoxemia; if the partial pressure of oxygen is below 40 mmHg, the patient has severe hypoxemia. Many clinical conditions may cause hypoxemia, such as emphysema, pulmonary obstruction, acute myocardial infarction, cerebral obstruction, etc. The main symptoms of hypoxemic patients are unconsciousness, dyspnea, chest tightness, chest pain, shortness of breath, wheezing, and cyanosis. If there are symptoms of hypoxemia, it is necessary to send to hospital for examination and treatment as soon as possible, and to give oxygen and other treatment measures to avoid delaying the best treatment time.