The indications for oxygen inhalation are the following three points: 1. Various reasons cause patients to have arterial partial pressure of oxygen lower than 60 mmHg or oxygen saturation lower than 90%, or oxygen saturation or oxygen partial pressure not reaching the expected value when breathing; 2. Patients with cardiovascular and cerebrovascular emergencies who suddenly develop chest pain, dyspnea and impaired consciousness; 3. Suspected cases of hypoxemia. The selection scheme of oxygen is mainly the following three points: 1. oxygen on demand; 2. short-term oxygen; 3. long-term oxygen. Oxygen on demand is based on the need of the disease and can be withdrawn when oxygen is not needed. Short-term oxygenation is to give oxygen therapy during the acute exacerbation of the disease, and oxygen can be stopped in the stable period. Long-term oxygen inhalation is for patients with chronic obstructive pulmonary disease or long-term lack of oxygen, and low-flow oxygen inhalation should be given for more than fifteen hours a day. There are three adverse effects of oxygen inhalation, hypercapnia, pulmonary atelectasis, and oxygen toxicity. Generally, it is due to the oxygen flow or oxygen concentration, which is not well regulated and will not be regulated. If you want to take oxygen at home, low-flow oxygen is 1-2L, and the maximum should not exceed 5L. If you are rescuing a patient in critical condition, you can adjust it higher.