Also to consider: The Legal Aspect.

I've been told that if you attempt to do CPR on a person and they die anyway, YOU can be SUED because you FAILED to perform CPR properly (or one of many other trumped up charges).

..And if you DO decide to risk litigation, you must continue doing CPR until EMTs arrive and take over.

If they had a DNR and you do CPR, you get sued.

If they didn't have DNR and you do CPR, and they die, you get sued.

No longer can anyone be a "Good Samaritan" without risk of being sued for not being "Good ENOUGH Samaritan".

Blech.