title: Higher vs lower positive end-expiratory pressure in patients with acute lung injury and acute respiratory distress syndrome: systematic review and meta-analysis.
abstract: BACKGROUND
  Trials comparing higher vs lower levels of positive end-expiratory pressure (PEEP) in adults with acute lung injury or acute respiratory distress syndrome (ARDS) have been underpowered to detect small but potentially important effects on mortality or to explore subgroup differences.
  
  
  OBJECTIVE
  To evaluate the association of higher vs lower PEEP with patient-important outcomes in adults with acute lung injury or ARDS who are receiving ventilation with low tidal volumes and to investigate whether these associations differ across prespecified subgroups.
  
  
  METHODS
  Search of MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials (1996-January 2010) plus a hand search of conference proceedings (2004-January 2010).
  
  
  METHODS
  Two reviewers independently screened articles to identify studies randomly assigning adults with acute lung injury or ARDS to treatment with higher vs lower PEEP (with low tidal volume ventilation) and also reporting mortality.
  
  
  METHODS
  Data from 2299 individual patients in 3 trials were analyzed using uniform outcome definitions. Prespecified effect modifiers were tested using multivariable hierarchical regression, adjusting for important prognostic factors and clustering effects.
  
  
  RESULTS
  There were 374 hospital deaths in 1136 patients (32.9%) assigned to treatment with higher PEEP and 409 hospital deaths in 1163 patients (35.2%) assigned to lower PEEP (adjusted relative risk [RR], 0.94; 95% confidence interval [CI], 0.86-1.04; P = .25). Treatment effects varied with the presence or absence of ARDS, defined by a value of 200 mm Hg or less for the ratio of partial pressure of oxygen to fraction of inspired oxygen concentration (P = .02 for interaction). In patients with ARDS (n = 1892), there were 324 hospital deaths (34.1%) in the higher PEEP group and 368 (39.1%) in the lower PEEP group (adjusted RR, 0.90; 95% CI, 0.81-1.00; P = .049); in patients without ARDS (n = 404), there were 50 hospital deaths (27.2%) in the higher PEEP group and 44 (19.4%) in the lower PEEP group (adjusted RR, 1.37; 95% CI, 0.98-1.92; P = .07). Rates of pneumothorax and vasopressor use were similar.
  
  
  CONCLUSIONS
  Treatment with higher vs lower levels of PEEP was not associated with improved hospital survival. However, higher levels were associated with improved survival among the subgroup of patients with ARDS.
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Matthias
authors.initials: M
authors.lastname: Briel
authors.forename: Maureen
authors.initials: M
authors.lastname: Meade
authors.forename: Alain
authors.initials: A
authors.lastname: Mercat
authors.forename: Roy G
authors.initials: RG
authors.lastname: Brower
authors.forename: Daniel
authors.initials: D
authors.lastname: Talmor
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Walter
authors.forename: Arthur S
authors.initials: AS
authors.lastname: Slutsky
authors.forename: Eleanor
authors.initials: E
authors.lastname: Pullenayegum
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhou
authors.forename: Deborah
authors.initials: D
authors.lastname: Cook
authors.forename: Laurent
authors.initials: L
authors.lastname: Brochard
authors.forename: Jean-Christophe M
authors.initials: JC
authors.lastname: Richard
authors.forename: Francois
authors.initials: F
authors.lastname: Lamontagne
authors.forename: Neera
authors.initials: N
authors.lastname: Bhatnagar
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Stewart
authors.forename: Gordon
authors.initials: G
authors.lastname: Guyatt
mesh_terms: D055371:Acute Lung Injury / Q000401:mortality / Q000628:therapy*; D000328:Adult; D000368:Aged; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000379:methods*; D016032:Randomized Controlled Trials as Topic; D012128:Respiratory Distress Syndrome / Q000401:mortality / Q000628:therapy*; D016019:Survival Analysis; D016896:Treatment Outcome