I am not a medical provessional, but the reason, as I was told, is the same reason as taking care in not rewarming the body core of a hypthermia victim too quickly, If the chilled blood residing in the limbs is circulated with compressions before it is sufficiently warmed, then when it reaches the heart it can cause heart or other organ failure.
As I am told by professionals, the frequent changes to CPR guidance are the result of constant study of successful sufvival cases and reactions by care givers and with what works in the majoriity of situations that marginally trained care providers can effect. The recent compresssions only advice is the result of understandable hesitancy by lay persons, who do not have the training or PPE equipment to provide safe (to themselves) rescue breathing to random strangers in medical need. It has been found that compressions only to circulate the oxygenated blood already persent within in the body may delay death long enough until advanced EMS arrives. Obvioiusly not effective or productive in a remote WFA situation.
The recommendation for no rescue breathing CPR is not only because of reluctance of bystanders to perform mouth to mouth resuscitation but also for a couple of other reasons.
First, in our modern mobile phone world it is increasingly common for bystanders to receive coaching remotely from a medical dispatcher by phone in instances of out of hospital cardiac arrest (OHCA). It is very difficult for individuals who have never received any on-hands education in rescue breathing to be able to assess airway patency and perform mouth to mouth breathing even minimally effectively.
Even those who have received hands-on instruction who have not actually performed rescue breathing in a real world situation would sometimes waste a lot of time trying to assess the airway and deliver even a few rescue breaths before initiating chest compressions.
While it is true that in most cases of OHCA, the vast majority of which are cardiac in origin, assuming that chest compressions can be initiated promptly the blood remains adequately oxygenated for some minutes and circulating that blood with chest compressions is beneficial. That is not the case in a drowning victim who has sustained cardiac arrest as a result of asphyxiation. In most of those instances the drowning victim had a healthy heart that was circulating blood up to the time that the blood oxygenation level dropped to the point that unconsciousness ensued followed by cessation of cardiac activity. In those instances the blood is desaturated to the point that circulating it with chest compressions without rescue breathing is basically pointless.
The success rate of any type of CPR for OHCA has improved slightly over the years but remains lower than many in the general public appreciate. One has to be careful in defining what constitutes "success". Many victims who receive CPR and have return of spontaneous circulation (ROSC) (which many would consider success) do not survive to hospital discharge, and some do not even survive to hospital admission. In one large world-wide meta-analysis looking at the survival of individuals receiving bystander CPR the survival rate in North America to hospital discharge was only 7.7%. Overall world-wide survival to discharge did improve from the period 1976-1979 to the period 2010-2019 but only very modestly, from 8.6% to 9.9%.
One thing that has been significant in increasing survival of individuals receiving bystander CPR is the wider availability of automated external defibrillators (AEDs). Many witnessed OHCAs are the result of a malignant, non-perfusing cardiac dysrhthymias. These individuals will generally not see a return to a perfusing cardiac rhythm unless defibrillated. Prompt defibrillation greatly enhances the chance of survival. It may well be that the modest improvement in survival of OHCA victims who have received bystander CPR over the preceding decade is due to the wider availability of AEDs alone.
As for the issue of chest-compression-only CPR versus conventional CPR, a meta-analysis appeared some years ago in the Lancet that analyzed three studies of dispatcher-assisted CPR in which the technique was randomized to one or the other method. The outcome was survival to hospital discharge. When these three studies were pooled in the meta-analysis the chest-compression-only technique showed a very modest survival benefit of 14% versus 12%, but when looks at the 95% confidence interval for the risk ratio between these groups (1.01-1.46) one sees that the difference barely achieved statistical significance. In the same paper the authors did a meta-analysis of seven other observational, non-randomized studies comparing the two techniques. In that meta-analysis no difference in survival to hospital discharge was observed between the two cohort groups, 8% versus 8%.
For adults with out-of-hospital cardiac arrest, instructions to bystanders from emergency medical services dispatch should focus on chest-compression-only CPR.
www.thelancet.com
There may be more recent data demonstrating evidence for a greater benefit for chest-compression-only bystander CPR for OHCA that I am not aware of.
