title: Alveolar recruitment in pulmonary and extrapulmonary acute respiratory distress syndrome: comparison using pressure-volume curve or static compliance.
abstract: BACKGROUND
  Alveolar recruitment in response to positive end-expiratory pressure (PEEP) may differ between pulmonary and extrapulmonary acute respiratory distress syndrome (ARDS), and alveolar recruitment values may differ when measured by pressure-volume curve compared with static compliance.
  
  
  METHODS
  The authors compared PEEP-induced alveolar recruitment in 71 consecutive patients identified in a database. Patients were classified as having pulmonary, extrapulmonary, or mixed/uncertain ARDS. Pressure-volume curves with and without PEEP were available for all patients, and pressure-volume curves with two PEEP levels were available for 44 patients. Static compliance was calculated as tidal volume divided by pressure change for tidal volumes of 400 and 700 ml. Recruited volume was measured at an elastic pressure of 15 cm H2O.
  
  
  RESULTS
  Volume recruited by PEEP (10 +/- 3 cm H2O) was 223 +/- 111 ml in the pulmonary ARDS group (29 patients), 206 +/- 164 ml in the extrapulmonary group (16 patients), and 242 +/- 176 ml in the mixed/uncertain group (26 patients) (P = 0.75). At high PEEP (14 +/- 2 cmH2O, 44 patients), recruited volumes were also similar (P = 0.60). With static compliance, recruitment was markedly underestimated and was dependent on tidal volume (226 +/- 148 ml using pressure-volume curve, 95 +/- 185 ml for a tidal volume of 400 ml, and 23 +/- 169 ml for 700 ml; P < 0.001).
  
  
  CONCLUSIONS
  In a large sample of patients, classification of ARDS was uncertain in more than one third of patients, and alveolar recruitment was similar in pulmonary and extrapulmonary ARDS. PEEP levels should not be determined based on cause of ARDS.
authors.affiliation: Réanimation Médicale, Assistance Publique-Hôpitaux de Paris, Hôpital Henri Mondor, France. arnaud.thille@orange.fr
authors.forename: Arnaud W
authors.initials: AW
authors.lastname: Thille
authors.forename: Jean-Christophe M
authors.initials: JC
authors.lastname: Richard
authors.forename: Salvatore M
authors.initials: SM
authors.lastname: Maggiore
authors.forename: V Marco
authors.initials: VM
authors.lastname: Ranieri
authors.forename: Laurent
authors.initials: L
authors.lastname: Brochard
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008170:Lung Compliance / Q000502:physiology*; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D011312:Pressure; D011650:Pulmonary Alveoli / Q000503:physiopathology*; D012128:Respiratory Distress Syndrome / Q000145:classification / Q000503:physiopathology*