title: Compressive forces and computed tomography-derived positive end-expiratory pressure in acute respiratory distress syndrome.
abstract: BACKGROUND
  It has been suggested that higher positive end-expiratory pressure (PEEP) should be used only in patients with higher lung recruitability. In this study, the authors investigated the relationship between the recruitability and the PEEP necessary to counteract the compressive forces leading to lung collapse.
  
  
  METHODS
  Fifty-one patients with acute respiratory distress syndrome (7 mild, 33 moderate, and 11 severe) were enrolled. Patients underwent whole-lung computed tomography (CT) scan at 5 and 45 cm H2O. Recruitability was measured as the amount of nonaerated tissue regaining inflation from 5 to 45 cm H2O. The compressive forces (superimposed pressure) were computed as the density times the sternum-vertebral height of the lung. CT-derived PEEP was computed as the sum of the transpulmonary pressure needed to overcome the maximal superimposed pressure and the pleural pressure needed to lift up the chest wall.
  
  
  RESULTS
  Maximal superimposed pressure ranged from 6 to 18 cm H2O, whereas CT-derived PEEP ranged from 7 to 28 cm H2O. Median recruitability was 15% of lung parenchyma (interquartile range, 7 to 21%). Maximal superimposed pressure was weakly related with lung recruitability (r = 0.11, P = 0.02), whereas CT-derived PEEP was unrelated with lung recruitability (r = 0.0003, P = 0.91). The maximal superimposed pressure was 12 ± 3, 12 ± 2, and 13 ± 1 cm H2O in mild, moderate, and severe acute respiratory distress syndrome, respectively, (P = 0.0533) with a corresponding CT-derived PEEP of 16 ± 5, 16 ± 5, and 18 ± 5 cm H2O (P = 0.48).
  
  
  CONCLUSIONS
  Lung recruitability and CT scan-derived PEEP are unrelated. To overcome the compressive forces and to lift up the thoracic cage, a similar PEEP level is required in higher and lower recruiters (16.8 ± 4 vs. 16.6 ± 5.6, P = 1).
authors: From the Dipartimento di Anestesia, Rianimazione (Intensiva e Subintensiva) e Terapia del Dolore, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy (D.C., P.C., L.G.); Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milan, Italy (M.C., E.C., C.C., M.A., M.B., L.G.); and Department of Anaesthesiology, Emergency and Intensive Care Medicine, Georg-August University of Göttingen, Göttingen, Germany (M.Q.).
authors: Massimo
authors: M
authors: Cressoni
authors: Davide
authors: D
authors: Chiumello
authors: Eleonora
authors: E
authors: Carlesso
authors: Chiara
authors: C
authors: Chiurazzi
authors: Martina
authors: M
authors: Amini
authors: Matteo
authors: M
authors: Brioni
authors: Paolo
authors: P
authors: Cadringher
authors: Michael
authors: M
authors: Quintel
authors: Luciano
authors: L
authors: Gattinoni
mesh_terms: D006801:Humans; D011175:Positive-Pressure Respiration / Q000379:methods*; D011312:Pressure; D001261:Pulmonary Atelectasis / Q000517:prevention & control; D012128:Respiratory Distress Syndrome / Q000503:physiopathology / Q000628:therapy*; D014057:Tomography, X-Ray Computed