PEEP has beneficial effects on inflammation in the injured and no deleterious effects on the noninjured lung after unilateral lung acid instillation.

Objective: In clinical lung injury areas of inflammation and structural alveolar alteration are unevenly distributed and interspaced between healthy or less injured lung areas. Positive end-expiratory pressure (PEEP) applied with mechanical ventilation (MV) may affect injured and healthy lung areas differently. We compared the effects of PEEP on the inflammatory response in injured and noninjured regions of the lung in an animal model of unilateral lung acid instillation.

Subjects: Anesthetized, paralyzed, and ventilated rats.

Interventions: Rats underwent left-endobronchial instillation with either hydrochloric acid or isotonic saline and were randomized 24 h later to MV using constant tidal volume (16 ml/kg) with either ZEEP, PEEP at 5 mmHg, or PEEP at 10 mmHg. After 4 h of MV the animals (n=9 or 10 per group) were killed and inflammatory markers assessed in left- and right-lung lavage fluid samples. In four additional animals per group differential lung perfusion was assessed.

Results: Unilateral acid injury alone worsened oxygenation, decreased left-lung perfusion, and increased left-lung lavage neutrophil and macrophage counts and cytokine levels. MV with ZEEP further impaired oxygenation and further decreased left-lung perfusion in acid-injured animals. MV with high PEEP preserved oxygenation and significantly decreased left-lung lavage protein content and cell counts in acid-injured animals and had no deleterious effect on the right (noninjured) lung.

Conclusion: In this model of unilateral lung acid injury high PEEP attenuates the inflammatory cell response in the acid-injured lung, preserved oxygenation and has no deleterious effects in the opposite lung.