The essence of life is the constant movement of the contradiction between assimilation and alienation in the body; And death is the end of this contradiction. The normal assimilation and alienation of tissues and organs in human body requires the respiratory and circulatory system to provide enough oxygen and raw materials, especially the central nervous system has poor tolerance to ischemia and hypoxia, so once breathing and heartbeat stop, it can immediately cause death.

So I think before the word brain death appeared, the so-called diagnostic criteria were breathing and heartbeat. Of course, I think China added a vein in ancient times! ! !

Under the condition that blood pressure can be measured, many countries have always regarded "cardiac arrest", "disappearance of breathing" and "zero blood pressure" as the standard of death.

Since the special committee of Harvard University to review the definition of death put forward the diagnostic index of brain death in 1968, more than 80 countries and regions in the world have successively formulated death standards, and some countries have also formulated corresponding laws on brain death, but some countries have adopted the standard of coexistence of brain death and respiratory death.

Because the artificial respirator can continue to maintain the cardiopulmonary function for a long time when other organs in the patient's body have failed, it has been widely believed in the legal field and all walks of life that the sign of the patient's death is the complete stop of brain function, especially the brain stem function. To declare a patient brain dead, doctors must have evidence of the structural or metabolic causes of brain injury, and must rule out the influence of drugs that may have anesthetic effect or muscle flaccid paralysis, especially the possibility of taking poison by themselves.