Brain death is an irreversible biological state of permanent and complete loss of brain and brainstem function. Brain death can be caused by any condition that results in widespread irreversible damage to the brain. Common causes of brain death include severe trauma, subarachnoid hemorrhage, cerebral hemorrhage, cerebral infarction, and ischemic-hypoxic encephalopathy. The main manifestations of brain death are coma and respiratory arrest, and the absence of cerebral stimulus responses, such as pupil dilation, loss of light reflex, absence of cough response to suction, and absence of convulsions, deafferentation, and other manifestations.