system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why is being 'brain dead' irreversible?
gpt
Brain-death isn't a diagnosis like a Coma or being Vegetative. Brain-Death occurs when the body is no longer receiving any electrical impulses from the brain and electrical function in the brain has ceased for the most part.

Parts of the brain can die and the rest still work the body. However if a significant enough portion of the brain were to die, then your body would have no way to respond.

The exact % of your brain required to be inoperable varies case to case. Brain Death has occured in people where they have sustained little brain injury at all, and yet there are people who are missing 80% of their Brain matter and still moving, talking and walking.

Brain Death, is very tricky to diagnose, because you are essentially calling the brain dead and the body is normally being kept alive by machine alone without end.