title: Positive end-expiratory pressure-induced functional recruitment in patients with acute respiratory distress syndrome.
abstract: OBJECTIVE
  In acute respiratory distress syndrome, alveolar recruitment improves gas exchange only if perfusion of the recruited alveolar units is adequate. To evaluate functional recruitment induced by positive end-expiratory pressure, we assessed pulmonary conductance for gas exchange based on lung diffusion for carbon monoxide and its components, including pulmonary capillary blood volume.
  
  
  METHODS
  Prospective, randomized, crossover study.
  
  
  METHODS
  Medical intensive care unit of a university hospital.
  
  
  METHODS
  Sixteen patients with lung injury/acute respiratory distress syndrome as well as eight control patients under invasive ventilation and eight healthy volunteers.
  
  
  METHODS
  Mechanical ventilation with two levels of positive end-expiratory pressure (5 and 15 cm H2O).
  
  
  RESULTS
  Lung diffusion for carbon monoxide and lung volumes, arterial blood gas analysis, and pressure-volume curves. In patients with acute respiratory distress syndrome, high positive end-expiratory pressure induced a 23% mean lung diffusion for carbon monoxide increase (4.4 +/- 1.7 mm Hg . min vs. 3.6 +/- 1.4 mL . mm Hg . min). In control patients and in healthy volunteers, lung diffusion for carbon monoxide values were (median [interquartile range]) 5.5 [3.8-8.0] mm Hg . min and 19.6 [15.1-20.6] mL . mm Hg . min, respectively. Among patients with acute respiratory distress syndrome, eight showed a >20% lung diffusion for carbon monoxide increase (responders) when increasing positive end-expiratory pressure. In the other eight, lung diffusion for carbon monoxide decreased or showed a <5% increase (nonresponders) with high positive end-expiratory pressure. Compared with nonresponders, responders at low positive end-expiratory pressure had smaller lungs with higher capillary blood volume-to-lung-volume ratio, higher values of the lower inflection point, and significantly greater increases in pulmonary capillary blood volume with high positive end-expiratory pressure. High positive end-expiratory pressure increased PaO2/Fio2 only in the responders.
  
  
  CONCLUSIONS
  The functional response to positive end-expiratory pressure in patients with acute lung injury/acute respiratory distress syndrome seems better when the lungs are smaller and with a higher capillary blood-volume-to-lung-volume ratio. Lung diffusion for carbon monoxide measurement supplies additional information about functional lung recruitment, which is not synonymous with mechanical recruitment.
authors.affiliation: Clinica di Malattie dell'Apparato Respiratorio, Ospedale San Paolo, Università degli Studi di Milano, Milan, Italy. fabiano.dimarco@unimi.it
authors.forename: Fabiano
authors.initials: F
authors.lastname: Di Marco
authors.forename: Jérôme
authors.initials: J
authors.lastname: Devaquet
authors.forename: Aissam
authors.initials: A
authors.lastname: Lyazidi
authors.forename: Fabrice
authors.initials: F
authors.lastname: Galia
authors.forename: Nathalia Pinto
authors.initials: NP
authors.lastname: da Costa
authors.forename: Roberto
authors.initials: R
authors.lastname: Fumagalli
authors.forename: Laurent
authors.initials: L
authors.lastname: Brochard
mesh_terms: D055371:Acute Lung Injury / Q000175:diagnosis / Q000401:mortality / Q000628:therapy*; D015331:Cohort Studies; D003422:Critical Care / Q000379:methods; D016638:Critical Illness / Q000401:mortality / Q000628:therapy; D018592:Cross-Over Studies; D005260:Female; D017052:Hospital Mortality; D006785:Hospitals, University; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D011175:Positive-Pressure Respiration / Q000379:methods*; D011336:Probability; D011379:Prognosis; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012121:Respiration, Artificial; D012128:Respiratory Distress Syndrome / Q000175:diagnosis / Q000401:mortality / Q000628:therapy*; D012129:Respiratory Function Tests; D018570:Risk Assessment; D018709:Statistics, Nonparametric; D015996:Survival Rate; D013990:Tidal Volume; D016896:Treatment Outcome