My understanding (and of course, I could be wrong) is that mag isn't really useful for COPD, only asthma (due to the fact that in COPD, the damage/constriction is chronic. In asthma, the constriction is more acute, thus responds better to mag). I've only initiated CPAP once prehospitally on a COPD patient, and I can say that the improvement was drastic on just 5 of PEEP. Went from gasping to sleeping/resting (not the "oh crap" resting of a respiratory patient, a legitimate "oh, they look comfortable!").