title: Effectiveness of emergency medical services for victims of out-of-hospital cardiac arrest: a metaanalysis.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Clinical Epidemiology Unit, Loeb Medical Research Institute, Ottawa Civic Hospital, Ontario, Canada.
authors.forename: G
authors.initials: G
authors.lastname: Nichol
authors.forename: A S
authors.initials: AS
authors.lastname: Detsky
authors.forename: I G
authors.initials: IG
authors.lastname: Stiell
authors.forename: K
authors.initials: K
authors.lastname: O'Rourke
authors.forename: G
authors.initials: G
authors.lastname: Wells
authors.forename: A
authors.initials: A
authors.lastname: Laupacis
mesh_terms: D016887:Cardiopulmonary Resuscitation; D004632:Emergency Medical Services / Q000458:organization & administration / Q000592:standards; D006323:Heart Arrest / Q000401:mortality / Q000628:therapy*; D006801:Humans; D008020:Life Support Care; D011930:Reaction Time; D016019:Survival Analysis