Why the hell couldn't they fork out a few bucks for a medical advisor?
Because yes, while the writers got it right about drowning in freezing water, I don't think I've ever seen a CPR rescue done so badly in a major film. Hardly any compressions, sporadic rescue breaths, inappropriate use of defibrillator, and lots of stopping to yell and emote.
Jeez, pay a nurse from your local ER a couple of hundred bucks to show you now to do it right, how hard is that!