title: Thoracic-impedance changes measured via defibrillator pads can monitor signs of circulation.
abstract: OBJECTIVE
  To investigate the potential for finding an alternative for the 'pulse check' during CPR, we studied the use of thoracic impedance measured via the defibrillator pads for circulation assessment during CPR.
  
  
  METHODS
  Transthoracic impedance, ECG and arterial pressures were recorded on 69 patients with a resulting data set of 434 segments. The circulatory-related impedance waveform was first isolated manually and features characterising its shape were suggested.
  
  
  RESULTS
  The features were correlated with corresponding blood pressure measurements, where a low, but significant, correlation coefficient (0.3) was found. By dividing the data set in groups of sufficient and insufficient circulation and using a neural network, we found that trends in features of the impedance waveform showed a discriminative potential for the two groups. Our classifier achieved a sensitivity of 90% for recognising insufficient circulation with a specificity of 82%.
  
  
  CONCLUSIONS
  We have shown that the circulation-related information found in the impedance signal may be used for circulatory assessment, especially the recognition of restoration of spontaneous circulation after cardiac arrest.
authors.affiliation: Department of Emergency Medicine, Medical University of Vienna, Austria.
authors.forename: Heidrun
authors.initials: H
authors.lastname: Losert
authors.forename: Martin
authors.initials: M
authors.lastname: Risdal
authors.forename: Fritz
authors.initials: F
authors.lastname: Sterz
authors.forename: Jon
authors.initials: J
authors.lastname: Nysaether
authors.forename: Klemens
authors.initials: K
authors.lastname: Köhler
authors.forename: Trygve
authors.initials: T
authors.lastname: Eftestøl
authors.forename: Cosima
authors.initials: C
authors.lastname: Wandaller
authors.forename: Helge
authors.initials: H
authors.lastname: Myklebust
authors.forename: Thomas
authors.initials: T
authors.lastname: Uray
authors.forename: Sven O
authors.initials: SO
authors.lastname: Aase
authors.forename: Anton N
authors.initials: AN
authors.lastname: Laggner
mesh_terms: D002307:Cardiography, Impedance / Q000295:instrumentation* / Q000379:methods; D016887:Cardiopulmonary Resuscitation; D047548:Defibrillators; D005260:Female; D006323:Heart Arrest / Q000628:therapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011674:Pulse; D013990:Tidal Volume