title: The biological effects of higher and lower positive end-expiratory pressure in pulmonary and extrapulmonary acute lung injury with intra-abdominal hypertension.
abstract: BACKGROUND
  Mechanical ventilation with high positive end-expiratory pressure (PEEP) has been used in patients with acute respiratory distress syndrome (ARDS) and intra-abdominal hypertension (IAH), but the role of PEEP in minimizing lung injury remains controversial. We hypothesized that in the presence of acute lung injury (ALI) with IAH: 1) higher PEEP levels improve pulmonary morphofunction and minimize lung injury; and 2) the biological effects of higher PEEP are more effective in extrapulmonary (exp) than pulmonary (p) ALI.
  
  
  METHODS
  In 48 adult male Wistar rats, ALIp and ALIexp were induced by Escherichia coli lipopolysaccharide intratracheally and intraperitoneally, respectively. After 24 hours, animals were anesthetized and mechanically ventilated (tidal volume of 6 mL/kg). IAH (15 mmHg) was induced and rats randomly assigned to PEEP of 5 (PEEP5), 7 (PEEP7) or 10 (PEEP10) cmH2O for 1 hour.
  
  
  RESULTS
  In both ALIp and ALIexp, higher PEEP levels improved oxygenation. PEEP10 increased alveolar hyperinflation and epithelial cell damage compared to PEEP5, independent of ALI etiology. In ALIp, PEEP7 and PEEP10 increased lung elastance compared to PEEP5 (4.3 ± 0.7 and 4.3 ± 0.9 versus 3.1 ± 0.3 cmH2O/mL, respectively, P <0.01), without changes in alveolar collapse, interleukin-6, caspase-3, type III procollagen, receptor for advanced glycation end-products, and vascular cell adhesion molecule-1 expressions. Moreover, PEEP10 increased diaphragmatic injury compared to PEEP5. In ALIexp, PEEP7 decreased lung elastance and alveolar collapse compared to PEEP5 (2.3 ± 0.5 versus 3.6 ± 0.7 cmH2O/mL, P <0.02, and 27.2 (24.7 to 36.8) versus 44.2 (39.7 to 56.9)%, P <0.05, respectively), while PEEP7 and PEEP10 increased interleukin-6 and type III procollagen expressions, as well as type II epithelial cell damage compared to PEEP5.
  
  
  CONCLUSIONS
  In the current models of ALI with IAH, in contrast to our primary hypothesis, higher PEEP is more effective in ALIp than ALIexp as demonstrated by the activation of biological markers. Therefore, higher PEEP should be used cautiously in the presence of IAH and ALI, mainly in ALIexp.
authors.forename: Cíntia Lourenco
authors.initials: CL
authors.lastname: Santos
authors.forename: Lillian
authors.initials: L
authors.lastname: Moraes
authors.forename: Raquel Souza
authors.initials: RS
authors.lastname: Santos
authors.forename: Cynthia
authors.initials: C
authors.lastname: dos Santos Samary
authors.forename: Johnatas Dutra
authors.initials: JD
authors.lastname: Silva
authors.forename: Marcelo Marcos
authors.initials: MM
authors.lastname: Morales
authors.forename: Vera Lucia
authors.initials: VL
authors.lastname: Capelozzi
authors.forename: Marcelo Gama
authors.initials: MG
authors.lastname: de Abreu
authors.forename: Alberto
authors.initials: A
authors.lastname: Schanaider
authors.forename: Pedro Leme
authors.initials: PL
authors.lastname: Silva
authors.forename: Cristiane Sousa Nascimento Baez
authors.initials: CS
authors.lastname: Garcia
authors.forename: Paolo
authors.initials: P
authors.lastname: Pelosi
authors.forename: Patricia Rieken Macedo
authors.initials: PR
authors.lastname: Rocco
mesh_terms: D055371:Acute Lung Injury / Q000150:complications* / Q000503:physiopathology / Q000628:therapy*; D000818:Animals; D017209:Apoptosis; D015415:Biomarkers / Q000378:metabolism; D004727:Endothelium / Q000473:pathology; D004848:Epithelium / Q000473:pathology; D005355:Fibrosis / Q000473:pathology; D007249:Inflammation / Q000378:metabolism; D059325:Intra-Abdominal Hypertension / Q000150:complications*; D008168:Lung / Q000473:pathology / Q000503:physiopathology; D008297:Male; D011175:Positive-Pressure Respiration; D017208:Rats, Wistar
chemical_list: D015415:Biomarkers