Alveolar wall disruption and lung inflammation associated with positive end-expiratory pressure and recruitment maneuver in pigs

Introduction

Different levels of positive end-expiratory pressure (PEEP) associated or not with alveolar recruitment maneuver (ARM) may have a significant impact on ventilator-induced lung injury [1], but this issue has not been well addressed in a model of lung injury using inhaled hydrochloric acid. We aimed to evaluate the effects of PEEP and ARM on respiratory mechanics and lung tissue in an inhaled hydrochloric acid acute lung injury (ALI) model.

Methods

Thirty-two pigs (22.9 ± 2.8 kg), were randomly allocated into one of four groups (I – Control-PEEP, II – Control-ARM, III – ALI-PEEP, IV – ALI-ARM). ALI was induced by intratracheal instillation of hydrochloric acid. PEEP values were progressively increased and decreased from 5, 10, 15 and 20 cmH₂O in all groups. Three alveolar recruitment maneuvers of 40 cmH₂O for 20 seconds were applied to the assigned groups at each interval of PEEP level increase or decrease. Histological analysis was made to evaluate the presence of inflammatory infiltrates, alveolar wall thickening, atelectasis, hemorrhage, alveolar edema and alveolar disruption. Histomorphometrical analyses of the lungs were also performed to determine alveolar dimensions.

Results

Inflammation and alveolar disruption were statistically greater in group II when compared with group I. There were no statistical differences between groups III and IV with respect to hemorrhage, alveolar edema, inflammation and alveolar disruption. Mean alveolar area and mean alveolar intercept were higher in group IV when compared with groups I and II (P < 0.05). The mean alveolar area was significantly smaller in the diaphragmatic lobes when compared with other middle and upper pulmonary lobes, but no statistical difference was found among groups.

Conclusion

The association of PEEP with ARM promoted a greater degree of alveolar disruption.