I know some one who was in cardiac arest, and it took the paramedics twelve minutes to revive him. He is now on full life suport. Is there any chance of a recovery with out brain damage and how long can a brain remain with out oxygen?

only God know that, hun.

There is a very slim chance for full recovery, the longer he requires life support, the slimmer the chance gets. If the doctors do an EEG they will have a better idea of his current brain function, and therefore a better idea of the potential for recovery.

Yes, with good CPR there is a good chance of recovery. Depends on how long it was before CPR was initiated. People are very surprising though and make recoveries in what seem impossible situations