Maintaining a body temperature of 40°C for 2-3 hours can affect the physiological functions of multiple systems, especially the central nervous system in young children. The body temperature continues to climb up to 40 ℃ metabolic rate increases, the human body will feel extremely uncomfortable, at this time may appear weakness, the whole body bone and joint and muscle pain and other symptoms. As the body is in a state of high metabolism, body fluids will also produce loss, if the fever is maintained for a short time, generally will not appear dehydration, if the fever lasts for a long time, there will be hypertonic dehydration, then need timely rehydration, otherwise it will lead to water-electrolyte metabolism disorders in the body, resulting in adverse consequences. In particular, children with persistent high fever of 40°C need to be given high clinical attention, and if not relieved in time, it may cause damage to brain cells and cause serious consequences. Therefore, patients with fever up to 40℃ are recommended to take appropriate relief measures in a timely manner, and if necessary, they can visit the hospital’s Infectious Diseases Department for symptomatic treatment by a professional doctor after clarifying the cause.