CPR is done in virtually every case with compression only. CPR with breaths interspersed with compressions is now all but abandoned.
Compression only CPR started during the beginning of the AIDS epidemic. At that time people became unwilling to do breaths with compressions and there became a need for evidence for CPR with compressions only. The scientific method requires an open mind when investigating a question but in this case a conclusion was necessary to support what had to be done. There is evidence but the evidence is biased, forced by circumstances.
Science based CPR would recommend compressions only CPR in cases of primary V-fib but breaths alone in cases of near drowning. Evidence for or against this would be misleading, manufactured as mandated by circumstance. We need to use science and common sense. We know that in primary V-fib, circulation suddenly stops but there is fully oxygenated blood present. Circulation via chest compressions as best as can be done makes sense for a time.
In near drowning, we know that the primary process involves breathing and the lack of oxygen. Rescue breathing makes sense. Anything that interferes with the delivery of effective rescue breathing is likely detrimental. It is tragic that simple rescue breathing is no longer employed in near drowning, costing many lives.
CPR has the unfortunate role of the psycho social response to many hopeless situations. It is sometimes obvious to the simplest of assessments that CPR would be fruitless. The guillotine comes to mind. There other reliable signs of futility that are less obvious. It is possible that a reliable sign such as rigor mortis, that is postmortem rigidity can is some cases be mistaken. Sometimes it is obvious and sometimes it is not. Casual, uneducated, arrogant, and judgmental observation by onlookers is all too often a fact of life. For this reason, resuscitation is sometimes carried out when the situation is in fact, recognized as hopeless by the appointed rescuer.