Effectiveness of Emergency Medical Services for Victims of Out-of-Hospital Cardiac Arrest: A Metaanalysis, , ,

Study objective: To determine the relative effectiveness of differences in response time interval, proportion of bystander CPR, and type and tier of emergency medical services (EMS) system on survival after out of hospital cardiac arrest. Methods: We performed a comprehensive literature search, excluding EMS systems other than those of interest (systems of interest were those comprising one tier with providers of basic life support [BLS] or advanced life support [ALS] and those comprising two tiers with providers of BLS or BLS-defibrillation followed by ALS), patient population of fewer than 100 cardiac arrests, studies in which we could not determine the total number of arrests of presumed cardiac origin, and studies lacking data on survival to hospital discharge. Metaanalysis using generalized linear model with dispersion estimation for random effects was then performed. Results: Increased survival to hospital discharge was significantly associated with tier (P<.01), response time interval (P <.01), and bystander CPR (P=.04). A significant interaction was detected between response time interval and bystander CPR (P=.02). For the studies analyzed, survival was 5.2% in a one-tier EMS system or 10.5% in a two-tier EMS system. A 1-minute decrease in mean response time interval was associated with absolute increases in survival rates of .4% and .7% in a one-tier and two-tier EMS systems, respectively. Conclusion: Increased survival to hospital discharge may be associated with decreased response time interval and with the use of a two-tier EMS system as opposed to a one-tier system. The data available for this analysis were suboptimal. Policymakers need more methodologically rigorous research to have more reliable and valid estimates of the effectiveness of different EMS systems. [Nichol G, Detsky AS, Stiell IG, OʹRourke K, Wells G, Laupacis A: Effectiveness of emergency medical services for victims of out-of-hospital cardiac arrest: A metaanalysis. Ann Emerg Med June 1996;27:700-710.] Heart disease is the most common cause of death in the United States.1 Such deaths are often due to cardiac arrest, the sudden cessation of cardiac mechanical activity manifested by the absence of a detectable pulse, unresponsiveness, and lack of breathing.2 Emergency medical services (EMS) systems have evolved into multifaceted advanced cardiac life support systems involving CPR, defibrillation, artificial ventilation, intubation, and administration of medication. Controversy exists about the effectiveness of different methods of emergency cardiac care because of wide variation in reported survival among centers3, ranging from 0%4 to 44%.5 This variation may be attributable to differences in the type of EMS system, proportion of victims receiving bystander CPR, response time intervals of providers, or geography of the city in question.6 Furthermore, different approaches to reporting survival make comparison of studies difficult.6, 7 and 8 A consensus conference has offered guidelines for uniform reporting of results to facilitate comparison of results.2 The purpose of this analysis was to estimate the relative effectiveness of the type and tier of an EMS system, unit response time interval of providers, and rate of bystander CPR on survival after out-of-hospital cardiac arrest. Using a protocol developed a priori, we performed a metaanalysis based on conventional techniques.9 and 10 The protocol comprised selection criteria for the primary studies, definitions of the primary endpoints, and an analysis plan.11 The metaanalysis was part of a larger cost-effectiveness analysis of improvements to EMS systems for out-of-hospital cardiac arrest. The results of the cost-effectiveness analysis are reported elsewhere.12 Definitions of terms The organization of an EMS system may vary both in the degree of training of the health care providers, as well as in the number of vehicles responding to a medical emergency. No universally accepted nomenclature exists for categorizing EMS systems, and some terms may have different meanings for different people. To facilitate clarity and understanding, the following terms are defined. Emergency health care providers vary in the degree of their training and may or may not transport patients to the hospital. Basic life support (BLS) providers administer oxygen and CPR to victims of cardiac arrest. Providers of BLS with defibrillation (BLS-D) defibrillate patients using automated or manual defibrillators. Finally, advanced life support (ALS) providers are trained to perform endotracheal intubation and to administer IV medications. BLS or BLS-D level care may be provided by emergency medical technicians (EMTs) in ambulances or by firefighters in pump vehicles or vans. Generally, ALS care is only provided by EMTs in ambulances. These personnel are referred to by others as "paramedics." The team that responds to a cardiac arrest in a given city may be part of a one-tier or two-tier EMS system. In a one-tier EMS system, a single provider and vehicle type responds to medical emergencies. In a two-tier system, two types of providers and/or vehicles respond. The vehicles may include ambulances, which respond from ambulance bases; or pump vehicles or vans, which respond from fire stations. In two-tier EMS systems, BLS providers (first tier) usually arrive more quickly because more generally are serving a community. In American cities with two-tier EMS systems, the second responding providers (second tier) have ALS capability. About 75% of the American urban population is served by a two-tier rather than by a one-tier EMS system.14 In this analysis we considered five configurations of EMS systems: (1) one tier with BLS providers, (2) one tier with BLS-D providers, (3) one tier with ALS providers, (4) two tiers with BLS followed by ALS (BLS + ALS) providers, and (5) two tiers with BLS-D followed by ALS (BLS-D + ALS) providers.