title: Positive end-expiratory pressure alters the severity and spatial heterogeneity of ventilator-induced lung injury: an argument for cyclical airway collapse.
abstract: OBJECTIVE
  Ventilator-induced lung injury (VILI) is a recognized complication of mechanical ventilation. Although the specific mechanism by which mechanical ventilation causes lung injury remains an active area of study, both alveolar overdistension and cyclical airway collapse and recruitment have been suggested as contributing causes. We hypothesized that mechanical ventilation in the absence of positive end-expiratory pressure (PEEP) causes VILI to be more severe and regionally variable as compared with PEEP = 8 cm H(2)O.
  
  
  METHODS
  To test this hypothesis, anesthetized, supine rabbits were mechanically ventilated with an end-inspiratory pressure of 28 cm H(2)O and either 0 or 8 cm H(2)O PEEP for 4 hours. Regional lung injury was determined by histologic scoring.
  
  
  RESULTS
  In the absence of PEEP, lung injury was regionally variable and greatest in the dorsal-caudal lung. This regional injury heterogeneity was abolished by the addition of PEEP = 8 cm H(2)O.
  
  
  CONCLUSIONS
  These results suggest that VILI is regionally heterogeneous and spatially correlates with regions in which cyclical airway collapse and recruitment is most likely to occur.
authors.affiliation: Department of Medicine, University of Tennessee, TN, USA. ssincla1@utmem.edu
authors.forename: Scott E
authors.initials: SE
authors.lastname: Sinclair
authors.forename: Emil
authors.initials: E
authors.lastname: Chi
authors.forename: Hen-I
authors.initials: HI
authors.lastname: Lin
authors.forename: William A
authors.initials: WA
authors.lastname: Altemeier