Sevoflurane reduces severity of acute lung injury possibly by impairing formation of alveolar oedema

Pulmonary oedema is a hallmark of acute lung injury (ALI), consisting of various degrees of water and proteins. Physiologically, sodium enters through apical sodium channels (ENaC) and is extruded basolaterally by a sodiumpotassiumadenosinetriphosphatase pump (Na+/K+-ATPase). Water follows to maintain iso-osmolar conditions and to keep alveoli dry. We postulated that the volatile anaesthetic sevoflurane would impact oedema resolution positively in an in-vitro and in-vivo model of ALI. Alveolar epithelial type II cells (AECII) and mixed alveolar epithelial cells (mAEC) were stimulated with 20 mu g/ml lipopolysaccharide (LPS) and co-exposed to sevoflurane for 8 h. In-vitro active sodium transport via ENaC and Na+/K+-ATPase was determined, assessing 22sodium and 86rubidium influx, respectively. Intratracheally applied LPS (150 mu g) was used for the ALI in rats under sevoflurane or propofol anaesthesia (8 h). Oxygenation index (PaO2/FiO2) was calculated and lung oedema assessed determining lung wet/dry ratio. In AECII LPS decreased activity of ENaC and Na+/K+-ATPase by 17.4% +/- 13.3% standard deviation and 16.2% +/- 13.1%, respectively. These effects were reversible in the presence of sevoflurane. Significant better oxygenation was observed with an increase of PaO2/FiO2 from 189 +/- 142 mmHg to 454 +/- 25 mmHg after 8 h in the sevoflurane/LPS compared to the propofol/LPS group. The wet/dry ratio in sevoflurane/LPS was reduced by 21.6% +/- 2.3% in comparison to propofol/LPS-treated animals. Sevoflurane has a stimulating effect on ENaC and Na+/K+-ATPase in vitro in LPS-injured AECII. In-vivo experiments, however, give strong evidence that sevoflurane does not affect water reabsorption and oedema resolution, but possibly oedema formation.