TL;DR CPR slightly increases the odds for someone otherwise healthy and young but is much less effective for the old and the chronically ill.
IIRC from prior CPR classes (own life data), 'correctly done' chest compressions are extremely violent, they often break ribs to get that compression of the heart between the rib cage and spine. It's a last-ditch effort with COSTS. If there's an AED around to use instead that would be FAR more preferable.
""" But the true odds are grim. In 2010 a review of 79 studies, involving almost 150,000 patients, found that the overall rate of survival from out-of-hospital cardiac arrest had barely changed in thirty years. It was 7.6%.
Bystander-initiated CPR may increase those odds to 10%. Survival after CPR for in-hospital cardiac arrest is slightly better, but still only about 17%. The numbers get even worse with age. A study in Sweden found that survival after out-of-hospital CPR dropped from 6.7% for patients in their 70s to just 2.4% for those over 90. Chronic illness matters too. One study found that less than 2% of patients with cancer or heart, lung, or liver disease were resuscitated with CPR and survived for six months. """