Brain death
Before diagnosing brain death, doctors will check for any other problem that could look like brain death (for example, a very low body temperature, or an overdose of sedatives).  They will usually wait six to 24 hours before checking again to make sure the person still has no signs of activity in the brain.  Then a second doctor is called in to do the same tests.  If both doctors agree, the patient can officially be diagnosed "brain dead."