The time of hyperbaric oxygen treatment for mild patients is usually about 3-5 days, and patients will have clinical symptoms such as dizziness, nausea, vomiting, headache and fatigue, etc. Patients with moderate poisoning will have typical clinical manifestations such as cherry-red lips and worsening headache. Patients with moderate poisoning will show typical clinical manifestations, which are cherry red color of lips and mouth, and they will have dizziness and worsening of headache, and the time of hyperbaric oxygen therapy is recommended to be around 7-10 days for patients with moderate poisoning. For severe patients, if coma and convulsions occur, hyperbaric oxygen treatment is required for a longer period of time, which should be 15 days or even more than 15 days to ensure that carbon monoxide poisoning is released and metabolized in the body. Mild poisoning can be fully recovered. Those with prolonged coma in severe cases are mostly suggestive of a serious prognosis, but a number of patients still recover. Recovery from delayed onset encephalopathy is slower. A few may retain persistent symptoms.