“When is a person in coma declared dead?”

I am so sorry for your situation. While you hear rare reports of people waking up after a long period of coma, it is very unusual.

Brain death is usually diagnosed by assessing their brainstem reflexes when a person is clearly not "waking up" otherwise. It may be that your sister has some brain stem reflexes after all this time. Having some reflexes does not mean she will wake up necessarily. It may mean that without support she will breath for a while on her own. She may continue breathing on her own. It is a very hard decision for you.

This is a very sad and difficult situation. Encephalopathy is when the brain activity is abnormal and a person is declared dead if brain activity both metabolic and electrical is absent. The goal of choosing a care plan is to respect the wishes of the sick person if that person had to make decisions.

A patient in a coma is not dead. They may be in a chronic vegetative state with no signs of meaningful activity or response, but still have some primitive brain function. Unfortunately, they do not recover and return to what we as families want to see as meaningful interaction and activity. Stopping the artificial means of life support is a difficult decision, but if they haven't shown any improvement in two years, it is unlikely to occur. What would your loved one want should be the best guide to help make a decision.

This is a complicated question and you really should speak at length with the doctors caring for your sister. It is easy to confuse coma with the term "brain dead." Coma means unresponsive to pain and other stimuli, but the patient still has some reflex activities, may breathe, and may react to pain (even though non purposeful). Brain dead, on the other hand, means no brain or brain stem activity--the pupils do not react to light, there is no response to a variety of stimuli. An EEG will show some residual electrical activity in a comatose patient, but in brain death, there is no electrical activity. Similarly, in brain death, tests show no circulation of blood to the brain. In the US, brain death is recognized as the equivalent of cardiac cessation death. Coma, on the other hand, is not the same. It sounds like what the doctors are proposing is that they stop supportive care (respirator, perhaps feeding, perhaps intravenous fluids, antibiotics and so on). This kind of discussion requires you understand what your sister's medical situation is. It is often helpful for some families if you include advisors, religious leaders or others whose opinions you value in making these decisions.