Before cryonics procedures can begin a patient must be legally dead. Legal death is a determination made by a legally qualified authority that a patient whose heart and lungs has stopped normal functioning cannot benefit from further medical care. The details of the determination depend upon care that is available, disease prognosis, and patient wishes (e.g., do-not-resuscitate order).
The legal status of cryonics care is after-death care. There is no legal ambiguity. However, philosophically, cryonics can be regarded as an attempt to continue care in hope of future resuscitation even after today’s medicine declares that it can do no more to resuscitate someone.
Physical conditions corresponding to legal death change over time. In the past, if someone stopped breathing, they were declared legally dead. Later, death became cessation of heartbeat. Today, a stopped heart can be restarted with CPR. As medical technology improves, the understanding of death changes.
Given the gap between today’s medical technology and the expected capabilities of future medical technology, the difference between present and future medical criteria for determination of death is likely to persist for some time (The future of death. J Crit Care. 2014;29(6):1111-3).
Under ideal conditions, cryonics procedures can begin shortly after the heart stops beating. Blood circulation and breathing can be artificially restored, keeping cells of the brain and body alive and functioning during the early stages of cryopreservation. Cryonics may also be performed after longer periods of legal death while retaining the possibility of future repair and resuscitation. Until information theoretic death occurs, there is reason to believe a cryopreserved person might be resuscitated in the future.