When the organism develops hypercapnia or hypoxemia, oxygen is administered to relieve the symptoms and prevent damage to various organs of the organism due to hypoxia. However, long-term over-oxygenation, at this time, may cause some damage to the organism and cause oxygen toxicity. Because of excessive oxygen, oxygen free radicals can be produced. When oxygen free radicals are very active in the body, they can kill and attack various tissues and cells, resulting in abnormal metabolic functions of tissues, cells, organs and systems of the organism, and even easily cause gene mutation and induce cancer. It can appear to have chest pain, cough, nausea, vomiting, dizziness, palpitations, and even feel coma, causing visual impairment, etc.