Efeitos da atelectasia sobre a lesão pulmonar induzida pela ventilação mecânica em um modelo de lesão pulmonar aguda induzida por lipopolissacarídeo

Abstract

In acute respiratory distress syndrome (ARDS), the lungs have a heterogeneous distribution of volumes and stress and thus, even protective ventilatory parameters such as low tidal volumes and limited plateau pressure might lead to lung injury. A theoretical model proposes that the transpulmonary pressure is not the same in the whole lung but it is multiplied in the interface between open and collapsed lung. Therefore, atelectatic areas could act as stress concentrators and triggers for ventilator induced lung injury (VILI). Objective: To compare lung injury between the periatelectasis and normoaerated lung regions in a model of atelectasis in rats with previously healthy lungs or acute lung injury (ALI) induced by lipopolysaccharides (LPS). Methods: Twenty-four rats were randomized into four groups, each of them with 6 animals: control for ALI and atelectasis (SAL-C): control for ALI with atelectasis (SALAT); ALI and control for atelectasis (LPS-C) and ALI with atelectasis (LPS-AT). ALI was induced by intraperitoneal injection of LPS. After 24 hours, atelectasis was induced by bronchial blocking. Animals underwent mechanical ventilation for 2 hours with protective parameters and the respiratory mechanics was monitored during this period. Thereafter, histologic analysis of two regions of interest, periatelectasis and normoaerated lung contralateral to atelectasis, was performed. Results: Lung injury score was significantly higher in the group LPS-C (0.41 ± 0.13) compared to its control SAL-C (0.15 ± 0.51) (p < 0.05). Periatelectasis regions showed higher lung injury score compared to the normoaerated regions in both groups SALAT (0.44 ± 0.06 x 0.27 ± 0.74; p < 0.05) and LPS-AT (0.56 ± 0.09 x 0.35 ± 0.04; p < 0.05). Lung injury score in periatelectatic regions were higher in the group LPS- AT (0.56 ± 0.09) compared to periatelectatic region of the group SAL-AT (0.44 ± 0.06) (p < 0.05). Conclusion: Atelectasis may cause injury to the surrounding tissue after a period of mechanical ventilation with protective parameters. Its effect was more significant in previously injured lungs.