title: Predictors of survival from out-of-hospital cardiac arrest: a systematic review and meta-analysis.
abstract: BACKGROUND
  Prior studies have identified key predictors of out-of-hospital cardiac arrest (OHCA), but differences exist in the magnitude of these findings. In this meta-analysis, we evaluated the strength of associations between OHCA and key factors (event witnessed by a bystander or emergency medical services [EMS], provision of bystander cardiopulmonary resuscitation [CPR], initial cardiac rhythm, or the return of spontaneous circulation). We also examined trends in OHCA survival over time.
  
  
  RESULTS
  An electronic search of PubMed, EMBASE, Web of Science, CINAHL, Cochrane DSR, DARE, ACP Journal Club, and CCTR was conducted (January 1, 1950 to August 21, 2008) for studies reporting OHCA of presumed cardiac etiology in adults. Data were extracted from 79 studies involving 142 740 patients. The pooled survival rate to hospital admission was 23.8% (95% CI, 21.1 to 26.6) and to hospital discharge was 7.6% (95% CI, 6.7 to 8.4). Stratified by baseline rates, survival to hospital discharge was more likely among those: witnessed by a bystander (6.4% to 13.5%), witnessed by EMS (4.9% to 18.2%), who received bystander CPR (3.9% to 16.1%), were found in ventricular fibrillation/ventricular tachycardia (14.8% to 23.0%), or achieved return of spontaneous circulation (15.5% to 33.6%). Although 53% (95% CI, 45.0% to 59.9%) of events were witnessed by a bystander, only 32% (95% CI, 26.7% to 37.8%) received bystander CPR. The number needed to treat to save 1 life ranged from 16 to 23 for EMS-witnessed arrests, 17 to 71 for bystander-witnessed, and 24 to 36 for those receiving bystander CPR, depending on baseline survival rates. The aggregate survival rate of OHCA (7.6%) has not significantly changed in almost 3 decades.
  
  
  CONCLUSIONS
  Overall survival from OHCA has been stable for almost 30 years, as have the strong associations between key predictors and survival. Because most OHCA events are witnessed, efforts to improve survival should focus on prompt delivery of interventions of known effectiveness by those who witness the event.
authors.affiliation: Departments of Emergency Medicine and Internal Medicine, University of Michigan, Ann Arbor, MI, USA. comilla@umich.edu
authors.forename: Comilla
authors.initials: C
authors.lastname: Sasson
authors.forename: Mary A M
authors.initials: MA
authors.lastname: Rogers
authors.forename: Jason
authors.initials: J
authors.lastname: Dahl
authors.forename: Arthur L
authors.initials: AL
authors.lastname: Kellermann
mesh_terms: D000368:Aged; D016887:Cardiopulmonary Resuscitation; D003695:Delivery of Health Care; D004632:Emergency Medical Services; D006323:Heart Arrest / Q000209:etiology / Q000401:mortality* / Q000628:therapy*; D006801:Humans; D008875:Middle Aged; D016017:Odds Ratio; D010343:Patient Admission; D010351:Patient Discharge; D017594:Publication Bias; D012044:Regression Analysis; D018570:Risk Assessment; D012307:Risk Factors; D016019:Survival Analysis; D017180:Tachycardia, Ventricular / Q000150:complications / Q000401:mortality / Q000628:therapy; D013997:Time Factors; D016896:Treatment Outcome; D014693:Ventricular Fibrillation / Q000150:complications / Q000401:mortality / Q000628:therapy