title: Assessment of respiratory system compliance with electrical impedance tomography using a positive end-expiratory pressure wave maneuver during pressure support ventilation: a pilot clinical study.
abstract: BACKGROUND
  Assessment of respiratory system compliance (Crs) can be used for individual optimization of positive end-expiratory pressure (PEEP). However, in patients with spontaneous breathing activity, the conventional methods for Crs measurement are inaccurate because of the variable muscular pressure of the patient. We hypothesized that a PEEP wave maneuver, analyzed with electrical impedance tomography (EIT), might be suitable for global and regional assessment of Crs during assisted spontaneous breathing.
  
  
  METHODS
  After approval of the local ethics committee, we performed a pilot clinical study in 18 mechanically ventilated patients (61 ± 16 years (mean ± standard deviation)) who were suitable for weaning with pressure support ventilation (PSV). For the PEEP wave, PEEP was elevated by 1 cmH2O after every fifth breath during PSV. This was repeated five times, until a total PEEP increase of 5 cmH2O was reached. Subsequently, PEEP was reduced in steps of 1 cmH2O in the same manner until the original PEEP level was reached. Crs was calculated using EIT from the global, ventral and dorsal lung regions of interest. For reference measurements, all patients were also examined during controlled mechanical ventilation (CMV) with a low-flow pressure-volume maneuver. Global and regional Crs(low-flow) was calculated as the slope of the pressure-volume loop between the pressure that corresponded to the selected PEEP and PEEP +5 cmH2O. For additional reference, Crs during CMV (Crs(CMV)) was calculated as expired tidal volume divided by the difference between airway plateau pressure and PEEP.
  
  
  RESULTS
  Respiratory system compliance calculated from the PEEP wave (Crs(PEEP wave)) correlated closely with both reference measurements (r = 0.79 for Crs(low-flow) and r = 0.71 for Crs(CMV)). No significant difference was observed between the mean Crs(PEEP wave) and the mean Crs(low-flow). However, a significant bias of +17.1 ml/cmH2O was observed between Crs(PEEP wave) and Crs(CMV).
  
  
  CONCLUSIONS
  Analyzing a PEEP wave maneuver with EIT allows calculation of global and regional Crs during assisted spontaneous breathing. In mechanically ventilated patients with spontaneous breathing activity, this method might be used for assessment of the global and regional mechanical properties of the respiratory system.
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Schleswig-Holstein, Campus Kiel, Arnold-Heller-Strasse 3, Haus 12, 24105, Kiel, Germany. tobias.becher@uksh.de.
authors.forename: Tobias H
authors.initials: TH
authors.lastname: Becher
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Schleswig-Holstein, Campus Kiel, Arnold-Heller-Strasse 3, Haus 12, 24105, Kiel, Germany. qtsbui@gmail.com.
authors.forename: Simon
authors.initials: S
authors.lastname: Bui
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Schleswig-Holstein, Campus Kiel, Arnold-Heller-Strasse 3, Haus 12, 24105, Kiel, Germany. Guenther.Zick@uksh.de.
authors.forename: Günther
authors.initials: G
authors.lastname: Zick
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Schleswig-Holstein, Campus Kiel, Arnold-Heller-Strasse 3, Haus 12, 24105, Kiel, Germany. Daniel.Blaeser@uksh.de.
authors.forename: Daniel
authors.initials: D
authors.lastname: Bläser
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Schleswig-Holstein, Campus Kiel, Arnold-Heller-Strasse 3, Haus 12, 24105, Kiel, Germany. Dirk.Schaedler@uksh.de.
authors.forename: Dirk
authors.initials: D
authors.lastname: Schädler
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Schleswig-Holstein, Campus Kiel, Arnold-Heller-Strasse 3, Haus 12, 24105, Kiel, Germany. Norbert.Weiler@uksh.de.
authors.forename: Norbert
authors.initials: N
authors.lastname: Weiler
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Schleswig-Holstein, Campus Kiel, Arnold-Heller-Strasse 3, Haus 12, 24105, Kiel, Germany. Inez.Frerichs@uksh.de.
authors.forename: Inéz
authors.initials: I
authors.lastname: Frerichs
mesh_terms: D000368:Aged; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D011175:Positive-Pressure Respiration / Q000379:methods*; D012121:Respiration, Artificial / Q000379:methods; D012131:Respiratory Insufficiency / Q000175:diagnosis* / Q000503:physiopathology*; D012137:Respiratory System / Q000503:physiopathology; D013990:Tidal Volume / Q000502:physiology*; D014054:Tomography / Q000379:methods*