Nrdsb4, a quick Google search on coding turned up the information that in a study of a large number of people who had gone into cardiac arrest (30,000 + people), the average length of CPR for those who had good brain function subsequently was 13 minutes. The average of those who had less favorable outcomes was 22 minutes. There was a case or perhaps cases where a person was restored to good brain function after 38 minutes. That was the longest this report contained.
I can see why they might continue for a total of 120 minutes, if Jahi’s heart keep restarting and then stopping.
This makes me aware that an Advanced Directive needs to be even more detailed than I would have guessed.
The 2 hours without blood supply to the brain comes from the news reports on Jahi’s case. That information is fairly widespread. It could of course be erroneous.