The results of this meta-analysis show that dispatcher-assisted chest compression-only bystander CPR is associated with improved survival after out-of-hospital cardiac arrest in adults patients compared to standard CPR (chest compression plus rescue ventilation).
Since meta-analyses are statistical tools for pooling existing evidence, we should consider the strength of the evidence favouring chest compression-only CPR. Despite the small number of trials included in this meta-analysis,14–16
the evidence favouring dispatcher-assisted chest compression-only CPR appears to be robust since all randomized clinical trials found a similar, albeit statistically non-significant, positive effect of chest compression-only CPR on survival. The effect size may appear small (~22%), but rates of survival after out-of-hospital cardiac arrest have been stagnating around 4–8 % for the last decades and thus a 22% increase in survival may actually represent an important progress. The incidence of cardiac arrest is about 0.5/1000 in North America.19
Extrapolating this number to include North America and the European Union (population: ~850 mio.), an absolute 2% increase of survival (as found in our meta-analysis), e.g. from 10% to 12% (20% relative increase), would mean an additional 8,000 lives saved per year.
The main reason why neither clinical trial showed a benefit of dispatcher-assisted chest compression-only CPR over standard CPR was probably because of lack of adequate power. The fact that only three clinical trials investigating dispatcher-assisted chest compression-only CPR have ever been conducted in out-of-hospital cardiac arrest, speaks for the difficulty of conducting well-designed prospective studies in this setting. Well identified challenges involve obtaining informed consent, the limited time to randomize patients, the fidelity of following the study protocol, the tracking of patients and outcomes and the difficulties in blinding the interventions. Because survival rates after out-of-hospital cardiac arrest are low and large treatment effects unlikely, very large sample sizes are required to show a statistically significant survival benefit. No chest compression-only clinical trial had more than 125 “events” (survivors) in a study arm, a number that may be considered fairly small for statistical analyses.
A second question that needs to be addressed is the plausibility of our findings. While being considered a controversial topic,20, 21
several independent lines of evidence suggest that chest compression-only CPR, assisted by dispatchers but perhaps also for non-assisted bystander CPR, may indeed be superior to standard bystander CPR in out-of-hospital cardiac arrest. Because this topic has been intensively discussed over the last few years, only the most pertinent explanations will be mentioned. The importance of uninterrupted, high-quality chest compressions for CPR success has been repeatedly documented.22–24
Limiting hands-off time, both for lay people and healthcare professionals, is an important predictor for survival after cardiac arrest. By avoiding rescue ventilations during CPR, which are commonly fairly time-consuming for lay bystanders,25
a continuous uninterrupted coronary perfusion pressure is maintained which increases the probability of a successful outcome.6
It should be noted that these considerations were the main reason to increase the compression:ventilation ratio for standard BLS from 15:2 to 30:2 in the 2005 resuscitation guidelines. All three dispatcher-assisted CPR trials used the old 15:2 ratio. It is unclear if using the current 30:2 ratio would have changed the results. Secondly, particularly for witnessed cardiac arrest it may be of less importance to provide oxygenation and ventilation during the first minutes than to provide high-quality chest compressions. Thirdly, chest compression-only CPR is easier to teach, to learn and to perform compared to the fairly complex standard CPR algorithm, thus increasing the chances of bystander to intervene and provide any CPR.
It is an interesting observation that our secondary meta-analysis that included only observational cohort studies and not randomized controlled trials, did not show any benefit of chest compression-only CPR compared to standard CPR. It needs, again, be pointed out that these observational studies did not investigate dispatcher-assisted bystander CPR, but aimed to investigate the chances of survival after out-of-hospital cardiac arrest between chest compression-only and standard CPR. In none of these studies, chest compression-only CPR had been taught to bystanders; rather, it was a deliberate decision of the lay bystander to avoid mouth-to-mouth rescue ventilation. While evidence suggests now that dispatcher-assisted chest compression-only CPR may be superior to standard CPR in adult out-of-hospital cardiac arrest, several special circumstances exist where chest compression-only CPR may not
be beneficial. Recent evidence from a large-scale prospective cohort study indicates that in cardiac arrest from non-cardiac causes, e.g., drowning, trauma, asphyxia, standard CPR may actually improve survival.26
Moreover, in paediatric out-of-hospital cardiac arrest which is also commonly of non-cardiac origin, a similar benefit may be conferred by standard CPR as well.27
Therefore, it appears that the benefits of chest compression-only bystander CPR are largest in adult patients suffering from “cardiac” arrest.
In summary, findings from this meta-analysis provide evidence that in adult out-of-hospital cardiac arrest dispatcher-assisted chest compression-only bystander CPR is associated with improved survival compared to standard CPR (chest compressions plus rescue ventilations). It is, however, unclear if unassisted chest compression-only bystander CPR provides similar survival benefits.