title: Lung recruitability is better estimated according to the Berlin definition of acute respiratory distress syndrome at standard 5 cm H2O rather than higher positive end-expiratory pressure: a retrospective cohort study.
abstract: OBJECTIVE
  The Berlin definition of acute respiratory distress syndrome has introduced three classes of severity according to PaO2/FIO2 thresholds. The level of positive end-expiratory pressure applied may greatly affect PaO2/FIO2, thereby masking acute respiratory distress syndrome severity, which should reflect the underlying lung injury (lung edema and recruitability). We hypothesized that the assessment of acute respiratory distress syndrome severity at standardized low positive end-expiratory pressure may improve the association between the underlying lung injury, as detected by CT, and PaO2/FIO2-derived severity.
  
  
  METHODS
  Retrospective analysis.
  
  
  METHODS
  Four university hospitals (Italy, Germany, and Chile).
  
  
  METHODS
  One hundred forty-eight patients with acute lung injury or acute respiratory distress syndrome according to the American-European Consensus Conference criteria.
  
  
  METHODS
  Patients underwent a three-step ventilator protocol (at clinical, 5 cm H2O, or 15 cm H2O positive end-expiratory pressure). Whole-lung CT scans were obtained at 5 and 45 cm H2O airway pressure.
  
  
  RESULTS
  Nine patients did not fulfill acute respiratory distress syndrome criteria of the novel Berlin definition. Patients were then classified according to PaO2/FIO2 assessed at clinical, 5 cm H2O, or 15 cm H2O positive end-expiratory pressure. At clinical positive end-expiratory pressure (11±3 cm H2O), patients with severe acute respiratory distress syndrome had a greater lung tissue weight and recruitability than patients with mild or moderate acute respiratory distress syndrome (p<0.001). At 5 cm H2O, 54% of patients with mild acute respiratory distress syndrome at clinical positive end-expiratory pressure were reclassified to either moderate or severe acute respiratory distress syndrome. In these patients, lung recruitability and clinical positive end-expiratory pressure were higher than in patients who remained in the mild subgroup (p<0.05). When patients were classified at 5 cm H2O, but not at clinical or 15 cm H2O, lung recruitability linearly increases with acute respiratory distress syndrome severity (5% [2-12%] vs 12% [7-18%] vs 23% [12-30%], respectively, p<0.001). The potentially recruitable lung was the only CT-derived variable independently associated with ICU mortality (p=0.007).
  
  
  CONCLUSIONS
  The Berlin definition of acute respiratory distress syndrome assessed at 5 cm H2O allows a better evaluation of lung recruitability and edema than at higher positive end-expiratory pressure clinically set.
authors.affiliation: 1Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Fondazione IRCCS Ca' Granda-Ospedale Maggiore Policlinico, Università degli Studi di Milano, Milan, Italy. 2Dipartimento di Anestesia, Rianimazione e Terapia del Dolore, Fondazione IRCCS Ca' Granda-Ospedale Maggiore Policlinico, Milan, Italy. 3Department of Anesthesiology, Emergency and Intensive Care Medicine, Georg-August University of Göttingen, Göttingen, Germany. 4Dipartimento di Radiologia, Fondazione IRCCS Ca' Granda-Ospedale Maggiore Policlinico, Milan, Italy. 5Departmentos de Anestesiologia y Medicina Intensiva, Facultad de Medicina, Pontificia, Universidad Catolica de Chile, Santiago, Chile. 6Dipartimento di Anestesia, Azienda Ospedaliera San Giovanni Battista-Molinette, Università degli Studi di Torino, Turin, Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: Caironi
authors.forename: Eleonora
authors.initials: E
authors.lastname: Carlesso
authors.forename: Massimo
authors.initials: M
authors.lastname: Cressoni
authors.forename: Davide
authors.initials: D
authors.lastname: Chiumello
authors.forename: Onner
authors.initials: O
authors.lastname: Moerer
authors.forename: Chiara
authors.initials: C
authors.lastname: Chiurazzi
authors.forename: Matteo
authors.initials: M
authors.lastname: Brioni
authors.forename: Nicola
authors.initials: N
authors.lastname: Bottino
authors.forename: Marco
authors.initials: M
authors.lastname: Lazzerini
authors.forename: Guillermo
authors.initials: G
authors.lastname: Bugedo
authors.forename: Michael
authors.initials: M
authors.lastname: Quintel
authors.forename: V Marco
authors.initials: VM
authors.lastname: Ranieri
authors.forename: Luciano
authors.initials: L
authors.lastname: Gattinoni
mesh_terms: D055371:Acute Lung Injury / Q000503:physiopathology; D000368:Aged; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D012128:Respiratory Distress Syndrome / Q000175:diagnosis / Q000503:physiopathology*; D012189:Retrospective Studies; D012720:Severity of Illness Index; D014057:Tomography, X-Ray Computed