According to the American Heart Assn, Using 2014 data, nearly 45 percent of out-of-hospital cardiac arrest victims survived when bystander CPR was administered.
I run on an ambulance service, we think it so important as to carry a Lucas Autopulse unit, https://www.lucas-cpr.com/
, I think the record for being on the machine is 8 hours and the PT recovered. It however is a violent machine in use, busted ribs are most certainly expected, but it can go on forever in it's compressions.
One reason folks don't think CPR works is they give up due to exhaustion before the PT arrives at the next level of care, hopefully a hospital. Before this machine, in a transport situation we used to have to stop every 5 minutes and do a Chinese fire drill, change the attendant in the back with the driver in order to keep continuous CPR going.
Having at least advanced first aid and CPR isn't a bad thing at all, if you're not the one actually treating the PT, you can at least help. Or not... Been boating since 1983, and fortunately I've never personally seen any serious medical conditions on the river, but I've heard stories from others. If memory serves, the most critical thing that's happened was a detached retina on last years Grand trip, we called the NPS and they choppered the gent out. Thankfully it was a false alarm and he was Ok, Most things are taken care of easily...