Brain death has been categorized into two groups.
There is the death of the cerebrum which in many jurisdictions defines brain death, the person's life can only be sustained artificially with life support equipment and then there is brainstem dead which means other organs could still be alive and functioning, such as the heart and the lungs.
Years ago if you lost your heart beat or stopped breathing you were considered dead. Today after a physical exam, which includes responses to pain and reflexes such as the pupillary response or fixed pupils, no corneal reflex, no eye movements and no coughing or respirations then you will be declared dead.
There are many states of the mind that mimic brain death; drug overdoses, alcohol intoxication, hypothermia, coma, and chronic vegetative states.
A doctors diagnosis should include
- no doubts of the patients condition
- no evidence of drugs
- Hypothermia must be eliminated
Once you lose consciousness and the ability to breathe, you're dead regardless if you're on life support or not.
Getting a flat line on an EEG test verifies you are brain dead and I take it that's when you'll start seeing the white light that you're supposed to gravitate towards.
Luckily, it takes two doctors to diagnose death. One to pull the plug and the other to bare, witness.