Survival with good neurological function following out-of-hospital CA requires a well coordinated approach to care, including citizen awareness, early access to CPR, defibrillation, and EMS, and optimal emergency department and post-resuscitation care.12, 14–22
Unfortunately, survival with good neurological function remains uncommon and understanding the epidemiology of cardiac arrest in specific communities, as in Denver, represents the first step in identifying ways to improve survival.
The results of this study demonstrate similar survival outcomes relative to other metropolitan communities in North America, and support utilization of a two-tiered EMS system split between fire-based BLS and hospital-based ALS. In addition, our system is relatively unique in that it uses fixed dispersal for BLS and dynamic dispersal for ALS, and the results of this study, to our knowledge, represents the first description of cardiac arrest survival using this type of system.
Two articles published in the 1990s provided insight into how different EMS systems impact survival following out-of-hospital CA, and both reported large variations in survival across several distinct EMS systems.23, 24
Both reviews classified EMS systems into one of five mutually exclusive systems using tiered response (one or two) and the level of training of the responders (basic emergency medical technicians (EMT), basic EMTs trained to use defibrillators, or paramedics). In both instances, the authors concluded that survival was greater in systems that used a two-tiered, BLS/ALS approach. Unfortunately, additional operational details of each EMS system were not provided in these reviews, making it difficult to know whether there are differences between fire- or non-fire-based systems or whether different dispersal mechanisms influence outcomes.
More recently, Persse et al.
reported the results of a study to compare survival following out-of-hospital CA due to VF between a uniform, “all ALS”, deployment strategy and a tiered deployment strategy within the same fire-based EMS system.25
Their study provided additional operational details related to deployment and how it may impact survival, although their EMS system was not split as it is with our system. The different cardiac arrest survival rates from other communities include a variety of EMS system structures that may influence survival.2,7,8
Unfortunately, it still remains unknown to what extent, if any, unique system differences, beyond the tiered approach, impact cardiac arrest survival.2,7,8
The characteristics of the population of cardiac arrest victims in Denver are comparable to those reported nationally.26
The annual incidence of out-of-hospital CA in North America ranges from approximately 5 to 20 per 10,000 (4 to 18 per 10,000 in Denver), and it is estimated that between 24% and 53% of all CAs are treated by EMS in North America (36% in Denver),26
between 20% and 38% of all arrests are due to VF or pVT (29% in Denver),27
approximately 27% receive bystander CPR (25% in Denver),3
and SHD in unselected adult populations is approximately 6% (8% in Denver).3, 6
Although the lack of uniformity in reporting arrest characteristics and survival makes comparisons to other published reports difficult, our findings of 27% SHD and 19% SHD with good neurologic recovery in patients with witnessed VF or pulseless VT also compare similarly to other communities as well.28
These findings, however, offer opportunities for focused efforts to further improve survival,29
including but not limited to the incorporation of “CPR First”,30, 31
“cardiocerebral” resuscitation strategies,21
early aggressive interventions in the emergency department,32, 33
implementation of standardized goal-directed post-resuscitation care15, 19
and therapeutic hypothermia.20, 34
During the study period, none of these potential strategies had been implemented in Denver.
Efforts to improve the timing and methods of delivery of CPR and defibrillation may also improve outcomes. Given the importance of CPR as a simple intervention with demonstrated efficacy, the small proportion of patients who received bystander CPR (26%) in our cohort, while similar to other large metropolitan communities, is disappointing, and further community-wide efforts to improve identification and bystander CPR are warranted.2, 35–38
Novel approaches to performing CPR and defibrillation have been recently described. Investigators in Seattle noted a survival increase among patients with VF following a CPR-defibrillation protocol change in 2005 that decreased the interval from shock to CPR and increased the duration of CPR between rhythm analyses.39, 40
Additionally, survival increased following the introduction of a minimally-interrupted cardiac resuscitation protocol in Arizona that emphasized primarily fewer interruptions in CPR.22
Training and continuous education in the performance of CPR and defibrillation for both first responders and paramedics may therefore further improve survival. In 2005, a protocol emphasizing uninterrupted CPR and CPR prior to defibrillation among patients with unwitnessed cardiac arrest was initiated in Denver. Results of this current evaluation provide the basis to compare the introduction of these new interventions on survival.
Training the public in CPR may be another method of improving survival, although the focus of these efforts remains a source of considerable debate.41
Although there are reports of successful school-based CPR training programs,42
some authors have suggested more focused CPR training strategies may be more cost-effective.43–45
Specific suggestions have focused on training high risk house-hold companions, the elderly, and those in specific occupations rather than mass training of unselected laypersons. It still remains unclear, however, how best to provide layperson CPR training in large communities in an effort to maximize survival.
Early access to defibrillation represents another critical “link” in the metaphorical chain of survival. Equipping Denver Fire first-responders with automated external defibrillators (AEDs) was initiated in 1996 and since 2000 all first-responding units in Denver have had defibrillation capabilities. Previous reports of equipping non-medical personnel (e.g., police officers, casino security officers, etc.) with AEDs, which resulted in the delivery of first defibrillation in a relatively short period of time, revealed a relatively high survival to hospital discharge percentage.46, 47
A recent meta-analysis also demonstrated that programs based on CPR plus early defibrillation with AEDs by trained non-healthcare professionals offer a significant survival advantage over CPR alone.48
These results substantiate the importance of further improving access to these critical interventions; however, effective and efficient implementation of such resources have not yet been clearly delineated and are likely community-specific.
Improving access to hospital-based medical services and post-resuscitative care may represent other opportunities to improve survival from CA. A recent commentary described the community as an important, powerful, and underappreciated factor in determining survival after cardiac arrest.8
As these authors pointed out, reporting of cardiac arrest survival statistics as we have done in this study may bring us closer to identifying and improving geographic variation in CA survival. There may be no single answer to improving cardiac arrest survival for all communities, although there are areas that deserve focus when attempting to maximize survival from CA. Each community may need to focus efforts and resources in somewhat different ways to achieve optimal success.