Prior to the invention of cardiopulmonary resuscitation (CPR), defibrillation, epinephrine (adrenaline) injection, and other treatments in the 20th century, the absence of blood circulation (and vital functions related to blood circulation) was historically considered the official definition of death.
With the advent of these strategies, cardiac arrest came to be called clinical dead rather than simply deceased, to reflect the possibility of post-arrest resuscitation.
Most tissues and organs of the body can survive clinical death for considerable periods. Blood circulation can be stopped in the entire body below the heart for at least 30 minutes, with injury to the spinal cord being a limiting factor.
Detached limbs may be successfully reattached after 6 hours with no circulation at warm temperatures. Bone, tendon, and skin can survive as long as 8 to 12 hours.
The brain, however, appears to accumulate ischemic (blood restriction) injury faster than any other organ. Without special treatment after circulation is restarted, full recovery of the brain after more than 3 minutes of clinical death at normal body temperature is rare.
Usually brain damage or later brain death results after longer intervals of clinical death even if the heart is restarted and blood circulation is successfully restored. Brain injury is therefore the chief limiting factor for recovery from clinical death.
Velma Thomas, of West Virginia, US, holds the record time for recovering from clinical death. In May 2008, Thomas went into cardiac arrest at her home. Medics were able to establish a faint pulse after eight minutes of CPR.
Her heart stopped twice after arriving at the hospital and she was placed on life support. Doctors attempted to lower her body temperature to prevent additional brain injury.
She was declared clinically dead for 17 hours after doctors failed to detect brain activity.
She was taken off life support and funeral arrangements were in progress. However, ten minutes after being taken off life support, she revived and recovered.
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