life support

Dear scholars, As-salamu `alaykum. There is a big controversy and debate among doctors and scholars regarding the exact definition of death. Doctors say that an individual is considered dead in one of the following two situations: complete irreversible cessation of respiratory and cardiovascular systems, or complete irreversible cessation of functions of the brain including the brain stem. In light of the above, what is the definition of death that justifies switching off life support? What are the other rulings related to the issue? Jazakum Allah khayran.