Effect of mechanical ventilation versus spontaneous breathing on abdominal edema and inflammation in ARDS : an experimental porcine model

BACKGROUND: Mechanical ventilation (MV), compared to spontaneous breathing (SB), has been found to increase abdominal edema and inflammation in experimental sepsis. Our hypothesis was that in primary acute respiratory distress syndrome (ARDS) MV would enhance inflammation and edema in the abdomen. METHODS: Thirteen piglets were randomized into two groups (SB and MV) after the induction of ARDS by lung lavage and 1 h of injurious ventilation. 1. SB: continuous positive airway pressure 15 cmH2O, fraction of inspired oxygen (FIO2) 0.5 and respiratory rate (RR) maintained at about 40 cycles min- 1 by titrating remifentanil infusion. 2. MV: volume control, tidal volume 6 ml kg- 1, positive end-expiratory pressure 15 cmH2O, RR 40 cycles min- 1, FIO2 0.5. MAIN OUTCOMES: abdominal edema, assessed by tissues histopathology and wet-dry weight; abdominal inflammation, assessed by cytokine concentration in tissues, blood and ascites, and tissue histopathology. RESULTS: The groups did not show significant differences in hemodynamic or respiratory parameters. Moreover, edema and inflammation in the abdominal organs were similar. However, blood IL6 increased in the MV group in all vascular beds (p < 0.001). In addition, TNFα ratio in blood increased through the lungs in MV group (+ 26% ± 3) but decreased in the SB group (- 17% ± 3). CONCLUSIONS: There were no differences between the MV and SB group for abdominal edema or inflammation. However, the systemic increase in IL6 and the TNFα increase through the lungs suggest that MV, in this model, was harmful to the lungs