title: Effect of Trigger Sensitivity on Redistribution of Ventilation During Pressure Support Ventilation Detected by Electrical Impedance Tomography.
abstract: BACKGROUND
  In supine position, pressure support ventilation causes a redistribution of ventilation towards the ventral regions of the lung. Theoretically, a less sensitive support trigger would cause the patient to breathe more actively, potentially attenuating the effect of positive pressure ventilation.
  
  
  OBJECTIVE
  To quantify the effect of trigger setting, we assessed redistribution of ventilation during pressure support ventilation (PSV) using electrical impedance tomography (EIT).
  
  
  METHODS
  With approval from the local ethics committee, six orthopedic patients were enrolled. All patients had general anesthesia with a laryngeal mask airway and a standardized anesthetic regimen (sufentanil, propofol and sevoflurane). Pressure support trigger settings varied between 2 and 15 L/minute and compared to unassisted spontaneous breathing. From EIT data, the center of ventilation (COV), the fraction of the total ventilation per region of interest (ROI) and intratidal gas distribution were calculated.
  
  
  RESULTS
  At all trigger settings, pressure support ventilation caused a significant ventral shift of the center of ventilation compared with during spontaneous breathing, confirmed by the analysis by regions of interest. During spontaneous breathing, COV was not different from baseline values obtained before induction of anesthesia. During PSV, the intratidal regional gas distribution (ITV-analysis) revealed subtle changes during the early inspiratory phase not detected by the COV-analysis.
  
  
  CONCLUSIONS
  Pressure support ventilation, but not spontaneous breathing, induces a significant redistribution of ventilation towards the ventral region. The sensitivity of the support trigger appears to influence the distribution of ventilation only during the early phase of inspiration.
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine,Klinikum Bremerhaven-Reinkenheide, Postbrookstr. 103, 27574 Bremerhaven, Germany ; Department of Anesthesia and Perioperative Care, San Francisco General Hospital, University of California San Francisco, San Francisco, California, USA ; Department of Anaesthesiology and Intensive Care Medicine, University Hospital, Technische Universitat Dresden, Germany.
authors.forename: Oliver C
authors.initials: OC
authors.lastname: Radke
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Hospital, Technische Universitat Dresden, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Schneider
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Hospital, Technische Universitat Dresden, Germany.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Vogel
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Hospital, Technische Universitat Dresden, Germany.
authors.forename: Thea
authors.initials: T
authors.lastname: Koch
keywords: Anesthesia, General; Pulmonary Atelectasis; Pulmonary Ventilation; Ventilator-Induced Lung Injury