CPR
Cardio Pulmonary Resuscitation

CPR is used to revive someone whose heart has stopped, or who has stopped breathing.  It can save lives.  However it can also result in brain damage from a period of time without blood circulation, or can bring one back to suffer through a long ICU stay requiring machines to breath, only to die a few months later.  You would expect a better CPR outcome if your heart stopped because of a momentary conduction problem - for example, an irregular heart beat that comes and goes, or an adverse effect of a medication.  On the other hand, if the heart stops because it is weak, that is not so good.  Indeed this is the case.  Success with CPR is not very strongly linked to age, but it is linked to one's "frailty".

The Clinical Frailty Scale (note that this scale does need individual interpretation!):

9: The most extreme frailty is when you are approaching end of life, which is expected within 6 months.

8: Completely dependent on others and approaching the end of life

7: Completely dependent on others (from physical or cognitive standpoint), but seem stable.

6: Needs help with all outside activities, cleaning the home or bathing.

5: Needs help with higher order activities of daily living - like transportation, heavy housework, taking medications.  Typically walking outside alone, meal preparation and housework are impaired somewhat.

4: While not dependent on others for daily help, symptoms often limit activities.

3: There are medical problems that are well controlled, but not regularly active beyond routine walking.

2: Have no active disease, may be very active occasionally.

1: Very robust, active, energetic, and motivated.  Exercise regularly.  Among the fittest for their age.

Those with frailty of 5-6 or higher on general have very poor outcomes from CPR.  In one study, not a single such frail person survived to be discharged from hospital after receiving CPR.  However, even people in their 80s with low frailty had similar survival rates to younger people (though long term survival is lower):

General statistics for CPR

Survival after CPR (to hospital discharge):  about 1 in 5-6 people  (can be 40% though for certain situations, though)

Of those who survive CPR:

Survival after 1 year: about 74%

Survival after 3 years: about 50% (62% for under 70 and 44% for over 70)

Neurologic function after CPR: about 80% of those who survive CPR will have at least enough neurologic function for independent living and at least part time work

CPR is an aggressive procedure: typically the ribs will be broken during the process, and there is an ICU stay with a tube in the throat and a machine doing the breathing can be quite traumatic as well.  Rehabilitation can also be a long haul.

Certainly CPR needs to be started as early as possible to have the best outcomes, and why there are training courses given widely.  And this is why CPR is performed by all first responders as a default unless someone presents with a "Do Not Resuscitate" form.

Do Not Resuscitate - this does not mean "do not care".  It just means that if the heart were to stop, CPR would not be attempted - but other measures, like IV antibiotics, fluids, and other medications, and oxygen masks can all be used.  If you do not want CPR to be performed, you can have a "DNR" form to have at home, so if first responders are called to an emergency and your heart stops, the form can be presented so they will not do resuscitation.  In hospital this form is not needed, you just need to tell your doctor that you would not want resuscitation if your heart stops, then this is recorded in your medical record (but only for that specific visit - after all, you are allowed to change your mind!)