The survival time of brain-dead patients on ventilator-assisted breathing varies and is closely related to their underlying disease, ranging from a few weeks to several months. The brain cells of brain dead patients are dead, but the heart cells are still alive, the heart muscle can be supplied with oxygen, and the whole body tissues and organs are still metabolizing normally. Therefore, after brain death, the heart may still be beating and the organs may not have completely failed. Respiratory arrest can be replaced by a ventilator to inflate the lungs to provide oxygen to the whole body and maintain the heartbeat. Brain death is irreversible damage, and without ventilator oxygenation, one’s own heart activity alone can only sustain life for a few minutes. Therefore, a brain-dead patient is already dead and a ventilator can only assist the patient to breathe and cannot revive him/her.