The effects of PEEP on inflammation and oxygenation during acute lung injury are not well known. Accordingly, we investigated the effect of different PEEP levels on local and systemic parameters of lung injury and inflammatory response in a unilateral in vivo lung injury model.

Male Wistar rats (350 g) underwent left-sided lung injury using endobronchial instillation of 0.4 ml HCl (pH 1) (study group) or endobronchial instillation of 0.1 ml NaCl 0.9% (placebo group). Twenty-four hours after treatment the rats were anesthetized, and intravascular catheters inserted for fluid infusion and hemodynamic monitoring. A tracheostomy was performed and the rats were ventilated for 4 hours with tidal volume of 6 ml/kg body weight and randomly assigned to ZEEP, PEEP = 5 cmH₂O or PEEP = 10 cmH₂O groups. Oxygenation was measured every 30 min and left and right lung lavage was performed lung after 4 hours of ventilation for cell and protein determination. An ANOVA was used for statistical analysis.

PaO₂ was higher in the PEEP groups as in the ZEEP groups. Protein and neutrophils in lung lavage fluid of both sides were higher in injured as in placebo rats. Increasing PEEP levels reduced neutrophil count in lavage fluid of the damaged lung in a dose dependent manner. PEEP increases oxygenation and decreased neutrophil infiltration in this model of lung injury.