Ischemic injury

Ischemia means inadequate or absent blood circulation that deprives tissue of oxygen and nutrients. At least several minutes of ischemia is an unavoidable part of cryonics because of the legal requirement that cryonics procedures do not begin until after blood circulation stops. The heart must stop beating so that legal death can be declared. When there is advance notice of impending clinical death, it is sometimes possible to deploy a team of technicians to perform a “standby”. The team artificially restores blood circulation and breathing using techniques similar to CPR as soon as possible after the heart stops..The aim is to keep tissues alive after legal death by analogy to conventional medical procedures in which viable organs and tissues are obtained for transplant from legally deceased donors. Contrary to popular belief, legal death does not mean that all the cells of the body have died.Often in cryonics the brain is without oxygen for many minutes at warm temperatures, or even hours if the heart stops unexpectedly. This causes ischemic injury to the brain and other tissues that makes resuscitation impossible by present medical technology. Cryonicists justify preservation under such conditions by noting recent advances that allow brain resuscitation after longer periods of ischemia than the traditional 4 to 6 minute limit, and persistence of brain structure and even some brain cell function after long periods of clinical death.They argue that definitions of death change as technology advances, and the early stages of what is called “death” today is actually a form of ischemic injury that will be reversible in the future.They claim that personal survival during long periods of clinical death is determined by information theoretic criteria