I work in a Level II Trauma ICU. We get the occasional brain dead patient on a vent secondary to an accidental trauma, heart attack, or some other event leading to that person's brain death. In determining brain death there are very, very specific criteria that have to be met. Most often at my facility we do a brain flow study. That is a quick and accurate verification of what the neurologist already suspects from signs on assessment of the patient.
Like many others with Neuro ICU experience have said, brain dead IS dead. Period. There is no possible way for that patient to have conscious thought processes. There is no possible way for that patient to 'wake up' ever again. At the point in time when their injury or whatever disease process they have caused a cessation of blood flow to the brain - that person was no more. They died right then and there. They will never be the person they were before that event happened. It is SO hard to explain that to families. Just look at how much disinformation is out there, even among us nurses!
As for talking to the brain dead patient. I do not. It is my belief that the person, the 'soul' of that body, has already left this Earth and is not 'hanging around' in the hospital room. It is my belief that the concsious person has 'left the building' and is long gone. At that point in time, I am working on constant resucitation of a body and nothing more. I am trying to keep organs alive in the case that we have gotten consent from the family in order to harvest. I do remain professional and respectful while doing that job, but I do not speak with the dead as though they are still alive.