title: Transthoracic impedance used to evaluate performance of cardiopulmonary resuscitation during out of hospital cardiac arrest.
abstract: BACKGROUND
  There is a need to measure cardiopulmonary resuscitation (CPR) in order to document whether ambulance personnel follow CPR guidelines. Our goal was to do this using defibrillator technology based on changes in transthoracic impedance (TTI) produced by chest compressions and ventilations.
  
  
  METHODS
  122 incidents of out-of-hospital cardiac arrest between May 2003 and February 2004 were analysed based on data recorded from defibrillators in Oslo EMS. New software was used to analyze chest compressions and ventilations based on changes in thoracic impedance between the defibrillator pads, as well as ECG and other event data.
  
  
  RESULTS
  In total, 25+/-14% (varying from 76% to 3%) of the time chest compressions were not performed on patients without spontaneous circulation (NFR=No Flow Ratio). When adjusting for time spent on analysis of ECG, pulse check and defibrillation, NFR was 20+/-13% (varying from 70% to 3%). Mean compressions delivered per minute was 87+/-16 and the compression rate during active compressions was 117+/-9min(-1). Individual variation was 31-117min(-1) (mean) and 95-144min(-1) (active periods). A mean of 14+/-3ventilations/min was recorded, varying from 8 to 26min(-1). Compared with the rest of the episode, the first 5min had a significantly higher proportion of time without chest compressions; 30+/-17% (p<0.001) and significantly lower mean compression and ventilation rates; 80+/-19min(-1) and 12+/-4min(-1), respectively (p<0.001 in both cases).
  
  
  CONCLUSIONS
  Core CPR values can be measured from TTI signals by using a standard defibrillator and new software. NFR was 25% (20% adjusted) with great rescuer variability.
authors.affiliation: National Competence Centre of Emergency Medicine, Institute for Experimental Medical Research, Ulleval University Hospital, 0027 Oslo, Norway.
authors.forename: Frederik S
authors.initials: FS
authors.lastname: Stecher
authors.forename: Jan-Aage
authors.initials: JA
authors.lastname: Olsen
authors.forename: Ronald E
authors.initials: RE
authors.lastname: Stickney
authors.forename: Lars
authors.initials: L
authors.lastname: Wik
mesh_terms: D002307:Cardiography, Impedance; D016887:Cardiopulmonary Resuscitation / Q000379:methods*; D004554:Electric Countershock; D004562:Electrocardiography; D004632:Emergency Medical Services / Q000379:methods*; D006323:Heart Arrest / Q000628:therapy*; D006801:Humans; D012984:Software