title: Thoracic impedance changes measured via defibrillator pads can monitor ventilation in critically ill patients and during cardiopulmonary resuscitation.
abstract: OBJECTIVE
  Monitoring of ventilation performance during cardiopulmonary resuscitation would be desirable to improve the quality of cardiopulmonary resuscitation. To investigate the potential for measuring ventilation rate and inspiration time, we calculated the correlation in waveform between transthoracic impedance measured via defibrillator pads and tidal volume given by a ventilator.
  
  
  METHODS
  Clinical study.
  
  
  METHODS
  Emergency department of a tertiary care university hospital.
  
  
  METHODS
  A convenience sample of mechanical ventilated patients (n = 32), cardiac arrest patients (n = 20), and patients after restoration of spontaneous circulation (n = 31) older than 18 were eligible.
  
  
  METHODS
  The Heartstart 4000SP defibrillator (Laerdal Medical Cooperation, Stavanger, Norway) with additional capabilities of recording thoracic impedance changes was used.
  
  
  RESULTS
  The relationship between impedance change and tidal volume (impedance coefficient) was calculated. The mean (sd) correlations between the impedance waveform and the tidal volume waveform in the patient groups studied were .971 (.027), .969 (.032), and .967 (.035), respectively. The mean (sd) impedance coefficient for all patients in the study was .00194 (.0078) Omega/mL, and the mean (sd) specific (weight-corrected) impedance coefficient was .152 (.048) Omega/kg/mL. The measured thorax impedance change for different tidal volumes (400-1000 mL) was approximately linear.
  
  
  CONCLUSIONS
  The impedance sensor of a defibrillator is accurate in identifying tidal volumes, when chest compressions are interrupted. This also allows quantifying ventilation rates and inspiration times. However this technology, at its present state, provides only limited practical means for exact tidal volume estimation.
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: Gottfried
authors.initials: G
authors.lastname: Sodeck
authors.forename: Anton N
authors.initials: AN
authors.lastname: Laggner
mesh_terms: D000328:Adult; D000368:Aged; D002307:Cardiography, Impedance / Q000295:instrumentation* / Q000379:methods; D016887:Cardiopulmonary Resuscitation; D016638:Critical Illness; D047548:Defibrillators; D004636:Emergency Service, Hospital; D005260:Female; D006323:Heart Arrest / Q000628:therapy*; D006801:Humans; D007442:Intubation, Intratracheal; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012121:Respiration, Artificial; D013990:Tidal Volume