title: A cumulative meta-analysis of the effectiveness of defibrillator-capable emergency medical services for victims of out-of-hospital cardiac arrest.
abstract: OBJECTIVE
  More than 1,000 patients experience sudden cardiac arrest each day. Treatment for this includes cardiopulmonary resuscitation (CPR) and emergency medical services (EMS) that provide CPR-basic life support (BLS), BLS with defibrillation (BLS-D), or advanced life support (ALS). Our previous systematic review of treatments for sudden cardiac arrest was limited by suboptimal data. Since then, debate has increased about whether bystander CPR is effective or whether attention should focus instead on rapid defibrillation. Therefore a cumulative meta-analysis was conducted to determine the relative effectiveness of differences in the defibrillation response time interval, proportion of bystander CPR, and type of EMS system on survival after out-of-hospital cardiac arrest.
  
  
  METHODS
  A comprehensive literature search was performed by using a priori exclusion criteria. We considered EMS systems that provided BLS-D, ALS, BLS plus ALS, or BLS-D plus ALS care. A generalized linear model was used with dispersion estimation for random effects.
  
  
  RESULTS
  Thirty-seven eligible articles described 39 EMS systems and included 33,124 patients. Median survival for all rhythm groups to hospital discharge was 6.4% (interquartile range, 3.7 to 10.3). Odds of survival were 1.06 (95% confidence interval [CI], 1.03 to 1.09; P <.01) per 5% increase in bystander CPR. Survival was constant if the defibrillation response time interval was less than 6 minutes, decreased as the interval increased from 6 to 11 minutes, and leveled off after 11 minutes (P <.01). Compared with BLS-D, odds of survival were as follows: ALS, 1. 71 (95% CI, 1.09 to 2.70; P =.01); BLS plus ALS, 1.47 (95% CI, 0.89 to 2.42; P =.07); and BLS with defibrillation plus ALS, 2.31 (95% CI, 1.47 to 3.62; P <.01.)
  
  
  CONCLUSIONS
  We confirm that greater survival after sudden cardiac arrest is associated with provision of bystander CPR, early defibrillation, or ALS. More research is required to evaluate the relative benefit of early defibrillation versus early ALS.
authors.affiliation: Clinical Epidemiology Unit, Loeb Health Research Institute, Division of General Internal Medicine, Ottawa, Ontario, Canada. grahamnichol@earthlink.net
authors.forename: G
authors.initials: G
authors.lastname: Nichol
authors.forename: I G
authors.initials: IG
authors.lastname: Stiell
authors.forename: A
authors.initials: A
authors.lastname: Laupacis
authors.forename: B
authors.initials: B
authors.lastname: Pham
authors.forename: V J
authors.initials: VJ
authors.lastname: De Maio
authors.forename: G A
authors.initials: GA
authors.lastname: Wells
mesh_terms: D004554:Electric Countershock; D004632:Emergency Medical Services; D006323:Heart Arrest / Q000401:mortality / Q000628:therapy*; D006801:Humans; D016014:Linear Models; D016019:Survival Analysis; D013997:Time Factors; D016896:Treatment Outcome; D014481:United States / Q000453:epidemiology