title: Influence of different electrode belt positions on electrical impedance tomography imaging of regional ventilation: a prospective observational study.
abstract: BACKGROUND
  Electrical impedance tomography (EIT) is a non-invasive bedside tool which allows an individualized ventilator strategy by monitoring tidal ventilation and lung aeration. EIT can be performed at different cranio-caudal thoracic levels, but data are missing about the optimal belt position. The main goal of this prospective observational study was to evaluate the impact of different electrode layers on tidal impedance variation in relation to global volume changes in order to propose a proper belt position for EIT measurements.
  
  
  METHODS
  EIT measurements were performed in 15 mechanically ventilated intensive care patients with the electrode belt at different thoracic layers (L1-L7). All respiratory and hemodynamic parameters were recorded. Blood gas analyses were obtained once at the beginning of EIT examination. Off-line tidal impedance variation/tidal volume (TV/VT) ratio was calculated, and specific patterns of impedance distribution due to automatic and user-defined adjustment of the colour scale for EIT images were identified.
  
  
  RESULTS
  TV/VT ratio is the highest at L1. It decreases in caudal direction. At L5, the decrease of TV/VT ratio is significant. We could identify patterns of diaphragmatic interference with ventilation-related impedance changes, which owing to the automatically adjusted colour scales are not obvious in the regularly displayed EIT images.
  
  
  CONCLUSIONS
  The clinical usability and plausibility of EIT measurements depend on proper belt position, proper impedance visualisation, correct analysis and data interpretation. When EIT is used to estimate global parameters like VT or changes in end-expiratory lung volume, the best electrode plane is between the 4th and 5th intercostal space. The specific colour coding occasionally suppresses user-relevant information, and manual rescaling of images is necessary to visualise this information.
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, Hannover Medical School, Carl-Neuberg-Str. 1, 30625, Hannover, Germany. karsten.jan@mh-hannover.de.
authors.forename: Jan
authors.initials: J
authors.lastname: Karsten
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, Hannover Medical School, Carl-Neuberg-Str. 1, 30625, Hannover, Germany. stueber.thomas@mh-hannover.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Stueber
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, Hannover Medical School, Carl-Neuberg-Str. 1, 30625, Hannover, Germany. voigt.nicolas@mh-hannover.de.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Voigt
authors.affiliation: Draeger Medical GmbH, Moislinger Allee 53, 23558, Lübeck, Germany. eckhard.teschner@draeger.com.
authors.forename: Eckhard
authors.initials: E
authors.lastname: Teschner
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University of Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany. hermann.heinze@uk-sh.de.
authors.forename: Hermann
authors.initials: H
authors.lastname: Heinze
mesh_terms: D000368:Aged; D004389:Durable Medical Equipment; D017097:Electric Impedance / Q000627:therapeutic use*; D004566:Electrodes; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D056888:Patient Positioning / Q000379:methods / Q000592:standards; D011175:Positive-Pressure Respiration / Q000379:methods*; D011446:Prospective Studies; D013990:Tidal Volume / Q000502:physiology; D014054:Tomography / Q000295:instrumentation* / Q000379:methods*