title: Lung recruitment in patients with the acute respiratory distress syndrome.
abstract: BACKGROUND
  In the acute respiratory distress syndrome (ARDS), positive end-expiratory pressure (PEEP) may decrease ventilator-induced lung injury by keeping lung regions open that otherwise would be collapsed. Since the effects of PEEP probably depend on the recruitability of lung tissue, we conducted a study to examine the relationship between the percentage of potentially recruitable lung, as indicated by computed tomography (CT), and the clinical and physiological effects of PEEP.
  
  
  METHODS
  Sixty-eight patients with acute lung injury or ARDS underwent whole-lung CT during breath-holding sessions at airway pressures of 5, 15, and 45 cm of water. The percentage of potentially recruitable lung was defined as the proportion of lung tissue in which aeration was restored at airway pressures between 5 and 45 cm of water.
  
  
  RESULTS
  The percentage of potentially recruitable lung varied widely in the population, accounting for a mean (+/-SD) of 13+/-11 percent of the lung weight, and was highly correlated with the percentage of lung tissue in which aeration was maintained after the application of PEEP (r2=0.72, P<0.001). On average, 24 percent of the lung could not be recruited. Patients with a higher percentage of potentially recruitable lung (greater than the median value of 9 percent) had greater total lung weights (P<0.001), poorer oxygenation (defined as a ratio of partial pressure of arterial oxygen to fraction of inspired oxygen) (P<0.001) and respiratory-system compliance (P=0.002), higher levels of dead space (P=0.002), and higher rates of death (P=0.02) than patients with a lower percentage of potentially recruitable lung. The combined physiological variables predicted, with a sensitivity of 71 percent and a specificity of 59 percent, whether a patient's proportion of potentially recruitable lung was higher or lower than the median.
  
  
  CONCLUSIONS
  In ARDS, the percentage of potentially recruitable lung is extremely variable and is strongly associated with the response to PEEP.
authors.affiliation: Istituto di Anestesiologia e Rianimazione, Fondazione Istituto di Ricovero e Cura a Carattere Scientifico, Ospedale Maggiore Policlinico, Mangiagalli, Regina Elena di Milano, Università degli Studi di Milano, Milan, Italy. gattinon@policlinico.mi.it
authors.forename: Luciano
authors.initials: L
authors.lastname: Gattinoni
authors.forename: Pietro
authors.initials: P
authors.lastname: Caironi
authors.forename: Massimo
authors.initials: M
authors.lastname: Cressoni
authors.forename: Davide
authors.initials: D
authors.lastname: Chiumello
authors.forename: V Marco
authors.initials: VM
authors.lastname: Ranieri
authors.forename: Michael
authors.initials: M
authors.lastname: Quintel
authors.forename: Sebastiano
authors.initials: S
authors.lastname: Russo
authors.forename: Nicolò
authors.initials: N
authors.lastname: Patroniti
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Cornejo
authors.forename: Guillermo
authors.initials: G
authors.lastname: Bugedo
mesh_terms: D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009929:Organ Size; D011014:Pneumonia / Q000473:pathology; D011175:Positive-Pressure Respiration / Q000379:methods; D012128:Respiratory Distress Syndrome / Q000473:pathology* / Q000503:physiopathology / Q000628:therapy; D012189:Retrospective Studies; D013990:Tidal Volume; D014057:Tomography, X-Ray Computed; D014109:Total Lung Capacity