The human brain is composed of six parts: the medulla oblongata, pons, midbrain, cerebellum, mesencephalon and telencephalon, with the medulla oblongata, pons and midbrain collectively referred to as the brainstem. The respiratory center of the human body is located in the brainstem, so damage to brainstem function can directly lead to the cessation of respiratory function. Unlike cells in some parts of the body that can be regenerated after damage, nerve cells cannot be regenerated once they are necrotic. Therefore, when a person suffers an irreversible injury to the brainstem, the brainstem is permanently and completely disabled, resulting in an irreversible loss of respiratory function. Subsequently, other organs and tissues of the body will also gradually lose their function due to the lack of oxygen supply. The clinical term brain death refers to the irreversible loss of function of the entire brain, including the brainstem. Brain death is different from “vegetative state”, where brainstem function exists and coma is only due to severe damage to the cerebral cortex or sudden inhibition, the patient can have voluntary breathing, heartbeat and brainstem response, while brain death has no voluntary breathing and is permanent and irreversible. Brain death is permanent and irreversible. In many countries, “cardiac arrest” and “loss of respiration” have been used as the criteria for death in the past. However, with the development of medical technology, the patient’s vital signs such as heartbeat, respiration and blood pressure can be reversed or maintained for a long time by a series of drugs and advanced equipment. However, if there is structural damage to the brainstem, nothing can be done to save the patient regardless of the medical treatment. Therefore, compared to cardiac death, brain death appears to be a more scientific and reliable criterion. The ability of artificial respirators to maintain cardiopulmonary function for long periods of time when all other organs of the patient’s body have failed has led to the widespread acceptance in jurisprudence and society that the hallmark of a patient’s death is the complete cessation of integrated brain function, especially brainstem function. To declare a patient brain dead, the physician must have evidence of structural or metabolic causes of brain damage, and must exclude all causes of reversible coma, such as acute intoxication (carbon monoxide poisoning, sedative sleeping drugs, narcotics, psychotropic drugs, muscle relaxants, etc.), hypothermia (anal temperature 32°C), severe electrolyte and acid-base balance disorders, metabolic and endocrine disorders (e.g., hepatic encephalopathy, uremic encephalopathy, non-ketogenic encephalopathy), and endocrine disorders, uremic encephalopathy, non-ketotic hyperglycemic encephalopathy) and shock, etc. Diagnostic criteria for brain death in China: Definition: Brain death is an irreversible loss of whole brain skills, including the brainstem. Prerequisites include: clear cause of coma and exclusion of reversible coma from all causes. Diagnostic criteria: deep coma, total loss of brainstem reflexes, and absence of voluntary breathing. All of the above must be present. Confirmation test, flat EEG, transcranial Doppler ultrasound with brain death pattern, and disappearance of waveforms above p14 of somatosensory evoked potentials. One of these three must be positive. Observation time of brain death: After the first diagnosis, no change in 12 hours of observation is required to confirm brain death. Diagnostic criteria of brain death in children The diagnosis of brain death in children should be more cautious and the following can be referred to: 1. Coma and respiratory arrest exist simultaneously. 2.All brainstem reflexes are gone, pupils are dilated and fixed, eyes are fixed, and respiratory activity is completely stopped. 3.The above examination results are constant and unchanged.