There was also an article on HN 6 months ago or something, where a doctor rescued a person in cardiac arrest by keeping her head cold enough using groceries just bought in the supermarket (if I remember correctly) - at about 25-30C. The person was successfully reanimated about 4 hours after the cardiac arrest and suffered no brain damage.
I have seen fist hand someone who had drowned, no pulse, being brought back with CPR. It happened to be ice cold glacial melt kayaking in the Alps that they had drowned in. Not 4 hours, but a significant amount of time without a pulse and breathing. Apparently he was OK afterwards.
