Inclusion Criteria:  patients present within 12 hours after acute carbon monoxide poisoning; age older than 16 years.  Exclusion Criteria:  pregnant women； patients receive oxygen therapy before presentation; have history of acute carbon monoxide poisoning within 1 year; have been diagnosed any of the following disease: Parkinson disease; cognitive disorder, psychiatric disorders, sequelae of cerebral infarction or hemorrhage, chronic kidney disease and receive hemodialysis, congestive heart failure ( NYHA class III-IV)