Brain death refers to the irreversible termination of the whole brain function, including the brainstem function. The respiratory center of human body is located in the brainstem, and the respiratory function of the patient will stop when brain death occurs. Therefore, the international criteria for judging brain death are: irreversible deep coma, no voluntary breathing, disappearance of brainstem reflexes, and disappearance of EEG activity. In China, death is also judged mainly by cardiac death before the doctor declares the patient dead, but in fact, the heart can continue to beat without oxygen deprivation, and breathing can be maintained with drugs and devices, as well as by ventilators. But once there is brain death, even if the vital signs are maintained by these devices, the patient will not get better, and this situation is actually a waste of medical resources.