title: Electrical impedance tomography monitoring in acute respiratory distress syndrome patients with mechanical ventilation during prolonged positive end-expiratory pressure adjustments.
abstract: OBJECTIVE
  The time required to reach oxygenation equilibrium after positive end-expiratory pressure (PEEP) adjustments in mechanically ventilated patients with acute respiratory distress syndrome (ARDS) is unclear. We used electrical impedance tomography to elucidate gas distribution and factors related to oxygenation status following PEEP in patients with ARDS.
  
  
  METHODS
  Nineteen mechanically ventilated ARDS patients were placed on baseline PEEP (PEEPB) for 1 hour, PEEPB - 4 cmH2O PEEP (PEEPL) for 30 minutes, and PEEPB + 4 cmH2O PEEP (PEEPH) for 1 hour. Tidal volume and respiratory rate were similar. Impedance changes, respiratory parameters, and arterial blood gases were measured at baseline, 5 minutes, and 30 minutes after PEEPL, and 5 minutes, 15 minutes, 30 minutes, and 1 hour after PEEPH.
  
  
  RESULTS
  PaO2/fraction of inspired oxygen (P/F ratio) decreased quickly from PEEPB to PEEPL, and stabilized 5 minutes after PEEPL. However the P/F ratio progressively increased from PEEPL to PEEPH, and a significantly higher P/F ratio and end-expiratory lung impedance were found at 60 minutes compared to 5 minutes after PEEPH. The end-expiratory lung impedance level significantly correlated with P/F ratio (p < 0.001). With increasing PEEP, dorsal ventilation significantly increased; however, regional ventilation did not change over time with PEEP level.
  
  
  CONCLUSIONS
  Late improvements in oxygenation following PEEP escalation are probably due to slow recruitment in ventilated ARDS patients. Electrical impedance tomography may be an appropriate tool to assess recruitment and oxygenation status in patients with changes in PEEP.
authors.affiliation: Medical Intensive Care Unit, Department of Internal Medicine, National Cheng Kung University Affiliated Hospital, Tainan, Taiwan.
authors.forename: Chia-Fu
authors.initials: CF
authors.lastname: Hsu
authors.affiliation: Medical Intensive Care Unit, Department of Internal Medicine, National Cheng Kung University Affiliated Hospital, Tainan, Taiwan.
authors.forename: Jen-Suo
authors.initials: JS
authors.lastname: Cheng
authors.affiliation: Medical Intensive Care Unit, Department of Internal Medicine, National Cheng Kung University Affiliated Hospital, Tainan, Taiwan.
authors.forename: Wei-Chi
authors.initials: WC
authors.lastname: Lin
authors.affiliation: Bioengineering Institute, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Yen-Fen
authors.initials: YF
authors.lastname: Ko
authors.affiliation: Bioengineering Institute, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Kuo-Sheng
authors.initials: KS
authors.lastname: Cheng
authors.affiliation: Institute of Clinical Medicine, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Sheng-Hsiang
authors.initials: SH
authors.lastname: Lin
authors.affiliation: Medical Intensive Care Unit, Department of Internal Medicine, National Cheng Kung University Affiliated Hospital, Tainan, Taiwan; Medical Device Innovation Center, College of Medicine, National Cheng Kung University, Tainan City, Taiwan. Electronic address: cwchen@mail.ncku.edu.tw.
authors.forename: Chang-Wen
authors.initials: CW
authors.lastname: Chen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017097:Electric Impedance; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000379:methods*; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging* / Q000628:therapy*; D013990:Tidal Volume; D014054:Tomography / Q000379:methods*
keywords: acute respiratory distress syndrome; electrical impedance tomography; positive end-expiratory pressure