title: Survival increases with CPR by Emergency Medical Services before defibrillation of out-of-hospital ventricular fibrillation or ventricular tachycardia: observations from the Resuscitation Outcomes Consortium.
abstract: BACKGROUND
  Immediate defibrillation is the traditional approach to resuscitation of cardiac arrest due to ventricular fibrillation or tachycardia (VF/VT). Delaying defibrillation to provide chest compressions may improve survival. We examined the effect of the duration of Emergency Medical Services (EMS) cardiopulmonary resuscitation (CPR) prior to first defibrillation on survival in patients with out-of-hospital VF/VT.
  
  
  METHODS
  From a prospective multi-center observational registry of EMS-treated out-of-hospital cardiac arrest, we identified 1638 EMS-treated cardiac arrests with first recorded rhythm VF/VT or "shockable" and complete data for analysis. Survival to hospital discharge was determined as a function of EMS CPR duration prior to first shock.
  
  
  RESULTS
  Compared to the reference group of first EMS CPR duration < or =45 s, the odds of survival was greater among patients who received between 46 and 195 s of EMS CPR before first shock (46-75 s odds ratio [OR] 1.15, 95% confidence interval [CI] 0.71-1.87; 76-105 s, OR 1.37, 95% CI 0.80-2.35; 106-135 s, OR 1.53, 95% CI 0.96-2.45; 136-165 s, OR 1.24, 95% CI 0.71-2.15; 166-195 s, OR 1.47, 95% CI 0.85-2.52). The benefit of EMS CPR before defibrillation was reduced when the duration of CPR exceeded 195 s (196-225 s, OR 0.95, 95% CI 0.47-1.81; 226-255 s, OR 0.91, 95% CI 0.46-1.79; 256-285 s, OR 0.46, 95% CI 0.17-1.29; 286-315 s, OR 1.29, 95% CI 0.59-2.85). An optimal EMS CPR duration was not identified and no duration achieved statistical significance.
  
  
  CONCLUSIONS
  In this observational analysis of VF/VT arrest, between 46 and 195 s of EMS CPR prior to defibrillation was weakly associated with improved survival compared to < or =45 s. Randomized trials are needed to confirm the optimal duration of EMS CPR prior to defibrillation and to assess the impact of first CPR duration on all initial rhythms.
authors.affiliation: University of Washington-Harborview Center for Prehospital Emergency Care, Department of Medicine, University of Washington, Seattle, WA, USA. smbradle@u.washington.edu
authors.forename: Steven M
authors.initials: SM
authors.lastname: Bradley
authors.forename: Erin E
authors.initials: EE
authors.lastname: Gabriel
authors.forename: Tom P
authors.initials: TP
authors.lastname: Aufderheide
authors.forename: Roxy
authors.initials: R
authors.lastname: Barnes
authors.forename: Jim
authors.initials: J
authors.lastname: Christenson
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Davis
authors.forename: Ian G
authors.initials: IG
authors.lastname: Stiell
authors.forename: Graham
authors.initials: G
authors.lastname: Nichol
mesh_terms: D000368:Aged; D016887:Cardiopulmonary Resuscitation; D004554:Electric Countershock; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015337:Multicenter Studies as Topic; D011446:Prospective Studies; D015996:Survival Rate; D017180:Tachycardia, Ventricular / Q000401:mortality* / Q000628:therapy*; D014693:Ventricular Fibrillation / Q000401:mortality* / Q000628:therapy*