title: Electrical impedance tomography during major open upper abdominal surgery: a pilot-study.
abstract: BACKGROUND
  Electrical impedance tomography (EIT) of the lungs facilitates visualization of ventilation distribution during mechanical ventilation. Its intraoperative use could provide the basis for individual optimization of ventilator settings, especially in patients at risk for ventilation-perfusion mismatch and impaired gas exchange, such as patients undergoing major open upper abdominal surgery. EIT throughout major open upper abdominal surgery could encounter difficulties in belt positioning and signal quality. Thus, we conducted a pilot-study and tested whether EIT is feasible in patients undergoing major open upper abdominal surgery.
  
  
  METHODS
  Following institutional review board's approval and written informed consent, we included patients scheduled for major open upper abdominal surgery of at least 3 hours duration. EIT measurements were conducted prior to intubation, at the time of skin incision, then hourly during surgery until shortly prior to extubation and after extubation. Number of successful intraoperative EIT measurements and reasons for failures were documented. From the valid measurements, a functional EIT image of changes in tidal impedance was generated for every time point. Regions of interest were defined as horizontal halves of the picture. Monitoring of ventilation distribution was assessed using the center of ventilation index, and also using the total and dorsal ventilated lung area. All parameter values prior to and post intubation as well as extubation were compared. A p < 0.05 was considered statistically significant.
  
  
  RESULTS
  A total of 120 intraoperative EIT measurements during major abdominal surgery lasting 4-13 hours were planned in 14 patients. The electrode belt was attached between the 2(nd) and 4(th) intercostal space. Consecutive valid measurements could be acquired in 13 patients (93%). 111 intraoperative measurements could be retrieved as planned (93%). Main obstacle was the contact of skin electrodes. Despite the high belt position, distribution of tidal volume showed a significant shift of ventilation towards ventral lung regions after intubation. This was reversed after weaning from mechanical ventilation.
  
  
  CONCLUSIONS
  Despite a high belt position, monitoring of ventilation distribution is feasible in patients undergoing major open upper abdominal surgery lasting from 4 to 13 hours. Therefore, further interventional trials in order to optimize ventilatory management should be initiated.
authors.affiliation: Department of Anaesthesiology, Duesseldorf University Hospital, Heinrich-Heine University Duesseldorf, Moorenstraße 5, Duesseldorf 40225, Germany.
authors.forename: Maximilian S
authors.initials: MS
authors.lastname: Schaefer
authors.affiliation: Department of Anaesthesiology, Duesseldorf University Hospital, Heinrich-Heine University Duesseldorf, Moorenstraße 5, Duesseldorf 40225, Germany.
authors.forename: Viktoria
authors.initials: V
authors.lastname: Wania
authors.affiliation: Department of Anaesthesiology, Duesseldorf University Hospital, Heinrich-Heine University Duesseldorf, Moorenstraße 5, Duesseldorf 40225, Germany.
authors.forename: Bea
authors.initials: B
authors.lastname: Bastin
authors.affiliation: Department of Anaesthesiology, Duesseldorf University Hospital, Heinrich-Heine University Duesseldorf, Moorenstraße 5, Duesseldorf 40225, Germany.
authors.forename: Ursula
authors.initials: U
authors.lastname: Schmalz
authors.affiliation: Department of Anaesthesiology, Duesseldorf University Hospital, Heinrich-Heine University Duesseldorf, Moorenstraße 5, Duesseldorf 40225, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Kienbaum
authors.affiliation: Department of Anaesthesiology, Duesseldorf University Hospital, Heinrich-Heine University Duesseldorf, Moorenstraße 5, Duesseldorf 40225, Germany ; Department of Anaesthesiology, Marienhospital Osnabrück, Bischofsstraße 1, Osnabrück 49074, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Beiderlinden
authors.affiliation: Department of Anaesthesiology, Duesseldorf University Hospital, Heinrich-Heine University Duesseldorf, Moorenstraße 5, Duesseldorf 40225, Germany.
authors.forename: Tanja A
authors.initials: TA
authors.lastname: Treschan
mesh_terms: D000005:Abdomen / Q000601:surgery*; D000368:Aged; D017097:Electric Impedance; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D061646:Operative Time; D010865:Pilot Projects; D012121:Respiration, Artificial / Q000379:methods*; D013990:Tidal Volume; D014054:Tomography / Q000379:methods*
keywords: Abdominal surgery; Atelectasis; Electrical impedance tomography; General anesthesia; Lung function