Multiple factors related to better outcome in out-of-hospital cardiac arrest—is mediation analysis the solution?

We thank Dr. Goto for his editorial in the Journal of Emergency and Critical Care Medicine entitled “Bystander Interventions for Out-of-Hospital Cardiac Arrests: Substantiated Critical Components of the Chain of Survival” (1), commenting on the recent New England Journal of Medicine manuscript “Bystander Efforts and 1-Year Outcomes in Out-of-Hospital Cardiac Arrest” conducted by our research group (2). Dr. Goto’s outline of the nationwide initiatives taken in Denmark during the last ten to fifteen years to increase rates of early resuscitative efforts by bystanders is extensively and accurately described. These initiatives include widespread voluntary and mandatory courses in basic life support, introduction and implementation of dispatch-assisted CPR, widespread automated external defibrillator (AED) dissemination and formation of an AED registry and linkage to emergency dispatch centers, enabling healthcare professionals to guide bystanders to the nearest AED (1-4). Bystander CPR and 30-day survival rates have more than tripled since the beginning of the past decade, where the Danish Cardiac Arrest Registry was established (5). In addition to the increased survival rates, Dr. Goto also highlighted from our recent New England Journal of Medicine manuscript that 30-day survivors were significantly less likely to be diagnosed with anoxic brain damage or admitted to a nursing home during the first year after out-of-hospital cardiac arrest (OHCA) had they received bystander CPR or bystander defibrillation relative to no bystander resuscitation (1,2).