Keep in mind that CPR is the bare minimum you can do to keep someone alive. If CPR is not performed properly the perfusion in the persons system is to low to keep them alive. Not giving enough breaths, compressions not deep enough, wrong hand placement on the compressions etc., all lead to bad CPR, which will result in permanent damage.
Using a AED (Automatic External Defibrilator) will help increase the chances of survival when used quickly, however there are only certain rythms that are shockable (Ventricular Fibrilation and Ventricular Tachycardia).
There are so many variables to CPR and keeping someone alive, technique, time etc that it is rarely keeping someone viable. There are some new advances in technology out there but most are used in small quantities. For example the new auto pulse CPR machine:
http://www.zoll.com/product.aspx?id=84
The problem is they are expensive. Sorry for my long post, just my training as a medic kicking in.
