title: Transthoracic impedance does not affect defibrillation, resuscitation or survival in patients with out-of-hospital cardiac arrest treated with a non-escalating biphasic waveform defibrillator.
abstract: OBJECTIVE
  This is a study of the influence of transthoracic impedance (TTI) on defibrillation, resuscitation and survival in patients with out-of-hospital cardiac arrest (OHCA), treated with a non-escalating impedance-compensating 150 J biphasic waveform defibrillator.
  
  
  METHODS
  Cardiac arrest data from two EMS systems were analyzed retrospectively. All witnessed arrests from patients who presented with a shockable rhythm and were treated initially by BLS personnel were included (n = 102). For each defibrillation and resuscitation outcome variable, we tested differences in mean TTI for successful versus unsuccessful outcome. The effect of call-to-shock time on overall outcome was also examined.
  
  
  RESULTS
  Initial shocks defibrillated 90% [83-95%] (95% confidence interval) of patients. Cumulative success with two shocks was 98% [93-100%] and with three shocks was 99% [95-100%]. TTI averaged 90 +/- 23 Omega. First-shock success, cumulative success through two shocks and cumulative success through the first-shock series were unrelated to TTI, as were BLS ROSC, pre-hospital ROSC, hospital admission and discharge. In contrast and consistent with previous findings, call-to-shock time was highly predictive of survival.
  
  
  CONCLUSIONS
  High impedance patients were defibrillated by the biphasic waveform used in this study at high rates with a fixed energy of 150 J and without energy escalation. Rapid defibrillation rather than differences in patient impedance accounts for resuscitation success.
authors.affiliation: Department of Anesthesiology, The Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905, USA. white.roger@mayo.edu
authors.forename: Roger D
authors.initials: RD
authors.lastname: White
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Blackwell
authors.forename: James K
authors.initials: JK
authors.lastname: Russell
authors.forename: David E
authors.initials: DE
authors.lastname: Snyder
authors.forename: Dawn B
authors.initials: DB
authors.lastname: Jorgenson
mesh_terms: D002307:Cardiography, Impedance / Q000706:statistics & numerical data*; D047548:Defibrillators / Q000706:statistics & numerical data*; D004554:Electric Countershock / Q000295:instrumentation* / Q000706:statistics & numerical data*; D004632:Emergency Medical Services / Q000379:methods / Q000706:statistics & numerical data*; D006323:Heart Arrest / Q000453:epidemiology / Q000628:therapy*; D006801:Humans; D008910:Minnesota / Q000453:epidemiology; D009657:North Carolina / Q000453:epidemiology; D010043:Outcome and Process Assessment, Health Care; D012151:Resuscitation / Q000706:statistics & numerical data*; D012189:Retrospective Studies; D016019:Survival Analysis; D016896:Treatment Outcome