title: High levels of PEEP may improve survival in acute respiratory distress syndrome: A meta-analysis.
abstract: OBJECTIVE
  Positive end-expiratory pressure (PEEP) has been viewed as an essential component of mechanical ventilation in acute respiratory distress syndrome (ARDS) and acute lung injury (ALI). However, clinical trials have not yet convincingly demonstrated that high PEEP levels improve survival. The object of this study was to test a priori hypotheses that a small but clinically important mortality benefit of high PEEP did exist, especially in patients with greater overall severity of illness and differences in PEEP protocols might have affected the study results.
  
  
  METHODS
  Meta-analysis of randomized controlled trials comparing high versus low PEEP in ARDS/ALI. Studies were identified by search of MEDLINE (1950-2008) and other sources.
  
  
  RESULTS
  Five studies including 2447 patients were identified. A pooled analysis showed a significant reduction in hospital mortality in favor of high PEEP (RR=0.89; 95% CI, 0.80-0.99; p=0.03). However, significant statistical and clinical heterogeneities such as differences in disease severity and ventilator protocols were found. The differences in PEEP protocols were not associated with differences in mortality rates. A logistic analysis suggested that the beneficial effect of high PEEP was greater in patients with higher ICU severity scores.
  
  
  CONCLUSIONS
  The statistical and clinical heterogeneities make proper interpretation of the results difficult. However, a small, but significant mortality benefit of high PEEP may exist. In addition, our analysis suggests the effects of high PEEP are greater in patients with higher ICU severity scores.
authors.affiliation: University of Missouri-Columbia, Division of Pulmonary, Critical Care and Environmental Medicine, Five Hospital Drive, CE 412, Columbia, MO 65212, USA. obay@health.missouri.edu
authors.forename: Yuji
authors.initials: Y
authors.lastname: Oba
authors.forename: Danish M
authors.initials: DM
authors.lastname: Thameem
authors.forename: Tareq
authors.initials: T
authors.lastname: Zaza
mesh_terms: D055371:Acute Lung Injury / Q000401:mortality* / Q000503:physiopathology / Q000628:therapy; D017052:Hospital Mortality; D006801:Humans; D011175:Positive-Pressure Respiration / Q000379:methods / Q000401:mortality*; D016032:Randomized Controlled Trials as Topic; D012121:Respiration, Artificial / Q000379:methods / Q000401:mortality; D012128:Respiratory Distress Syndrome / Q000401:mortality* / Q000503:physiopathology / Q000628:therapy; D012720:Severity of Illness Index; D014481:United States