title: Mechanical ventilation guided by electrical impedance tomography in experimental acute lung injury.
abstract: OBJECTIVE
  To utilize real-time electrical impedance tomography to guide lung protective ventilation in an animal model of acute respiratory distress syndrome.
  
  
  METHODS
  Prospective animal study.
  
  
  METHODS
  Animal research center.
  
  
  METHODS
  Twelve Yorkshire swine (15 kg).
  
  
  METHODS
  Lung injury was induced with saline lavage and augmented using large tidal volumes. The control group (n = 6) was ventilated using ARDSnet guidelines, and the electrical impedance tomography-guided group (n = 6) was ventilated using guidance with real-time electrical impedance tomography lung imaging. Regional electrical impedance tomography-derived compliance was used to maximize the recruitment of dependent lung and minimize overdistension of nondependent lung areas. Tidal volume was 6 mL/kg in both groups. Computed tomography was performed in a subset of animals to define the anatomic correlates of electrical impedance tomography imaging (n = 5). Interleukin-8 was quantified in serum and bronchoalveolar lavage samples. Sections of dependent and nondependent regions of the lung were fixed in formalin for histopathologic analysis.
  
  
  RESULTS
  Positive end-expiratory pressure levels were higher in the electrical impedance tomography-guided group (14.3 cm H₂O vs. 8.6 cm H₂O; p < 0.0001), whereas plateau pressures did not differ. Global respiratory system compliance was improved in the electrical impedance tomography-guided group (6.9 mL/cm H₂O vs. 4.7 mL/cm H₂O; p = 0.013). Regional electrical impedance tomography-derived compliance of the most dependent lung region was increased in the electrical impedance tomography group (1.78 mL/cm H₂O vs. 0.99 mL/cm H₂O; p = 0.001). Pao₂/FIO₂ ratio was higher and oxygenation index was lower in the electrical impedance tomography-guided group (Pao₂/FIO₂: 388 mm Hg vs. 113 mm Hg, p < 0.0001; oxygentation index, 6.4 vs. 15.7; p = 0.02) (all averages over the 6-hr time course). The presence of hyaline membranes (HM) and airway fibrin (AF) was significantly reduced in the electrical impedance tomography-guided group (HMEIT 42% samples vs. HMCONTROL 67% samples, p < 0.01; AFEIT 75% samples vs. AFCONTROL 100% samples, p < 0.01). Interleukin-8 level (bronchoalveolar lavage) did not differ between the groups. The upper and lower 95% limits of agreement between electrical impedance tomography and computed tomography were ± 16%.
  
  
  CONCLUSIONS
  Electrical impedance tomography-guided ventilation resulted in improved respiratory mechanics, improved gas exchange, and reduced histologic evidence of ventilator-induced lung injury in an animal model. This is the first prospective use of electrical impedance tomography-derived variables to improve outcomes in the setting of acute lung injury.
authors.affiliation: Department of Anesthesiology, Perioperative and Pain Medicine, Division of Critical Care Medicine, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA. gerhard.wolf@childrens.harvard.edu
authors.forename: Gerhard K
authors.initials: GK
authors.lastname: Wolf
authors.forename: Camille
authors.initials: C
authors.lastname: Gómez-Laberge
authors.forename: Jordan S
authors.initials: JS
authors.lastname: Rettig
authors.forename: Sara O
authors.initials: SO
authors.lastname: Vargas
authors.forename: Craig D
authors.initials: CD
authors.lastname: Smallwood
authors.forename: Sanjay P
authors.initials: SP
authors.lastname: Prabhu
authors.forename: Sally H
authors.initials: SH
authors.lastname: Vitali
authors.forename: David
authors.initials: D
authors.lastname: Zurakowski
authors.forename: John H
authors.initials: JH
authors.lastname: Arnold
mesh_terms: D055371:Acute Lung Injury / Q000000981:diagnostic imaging / Q000473:pathology* / Q000628:therapy*; D000704:Analysis of Variance; D000818:Animals; D001707:Biopsy, Needle; D016001:Confidence Intervals; D004195:Disease Models, Animal; D017097:Electric Impedance; D007150:Immunohistochemistry; D018836:Inflammation Mediators / Q000378:metabolism; D011175:Positive-Pressure Respiration / Q000379:methods; D011897:Random Allocation; D012016:Reference Values; D034421:Sus scrofa; D013552:Swine; D013990:Tidal Volume; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D018836:Inflammation Mediators