Efeitos da ventilação em posição prona na lesão pulmonar aguda leve induzida por injeção de lipopolysaccharide intraperitoneal em ratos Wistar

Abstract

Introduction: Prone position has been studied as a ventilator strategy among patients with acute respiratory distress syndrome. The benefits of prone position ventilation, including reduction in the mortality, are well demonstrated in the severe but not in milder forms of this syndrome. We therefore investigated the effects of the prone position on arterial blood gases, lung inflammation and histology in an experimental model of mild acute lung injury in rats. Methods: Acute lung injury was induced in adult male Wistar rats by intraperitoneal Escherichia coli lipopolysaccharide injection (5 mg/kg). After 24h, the animals with PaO2/FIO2 between 200 and 300 mmHg were anesthetized and randomized into 2 groups according to their position during ventilation (prone [n=6] and supine [n=6]). Both groups were compared to a control group (n=5) that received intraperitoneal saline and was ventilated in the supine position. All of the groups were ventilated for 1h with volume-controlled ventilation mode, with tidal volume of 6 ml/kg, respiratory rate of 80 breaths/min, positive end-expiratory pressure of 5 cmH2O, and an inspired oxygen fraction of 1. Results: Significantly higher lung injury scores were observed in the LPS-supine group compared to LPS-prone and control groups (0.32 ± 0.03; 0.17 ± 0.03 and 0.13 ± 0.04, respectively) (p<0.001), mainly due to a higher neutrophil infiltration level in the interstitial space and more proteinaceous debris in the airspaces. Similar differences were observed when the gravitational dependent lung regions (dorsal in the supine group and ventral in the prone group – 0.34 ± 0.05 and 0.22 ± 0.04, respectively) (p < 0.05) and non-dependent lung regions (ventral in the supine group and dorsal in the prone group – 0.29 ± 0.04 and 0.13 ± 0.04, respectively) (p < 0.05) were analyzed separately. The BAL neutrophil content was also higher in the LPS-supine group compared to the LPSprone and control groups. There were no significant differences in the wet/dry ratio and gas exchange levels among the three groups. CONCLUSIONS: In this experimental extrapulmonary mild acute lung injury model, prone position ventilation for 1 hour, when compared with supine position ventilation, was associated with lower lung inflammation and injury, but without any impact on arterial oxygenation and lung edema.