The effect of mechanical ventilation on the abdominal organs

During mechanical ventilation (MV), the interplay between abdomen and thorax has been studied unilaterally focusing on the effect that an increased abdominal pressure would have on the thorax. Only a small cluster of studies offered a different perspective showing a lower inflammation and a better lymphatic clearance of edema in abdominal organs when spontaneous breathing was applied compared to MV. Apart from these insights, a deeper understanding of the effect of different MV features on the abdominal organs remains uninvestigated.The aims of the thesis were: to investigate how changes in perfusion and edema influence inflammation and affect each other, and to examine how the management of ARDS could affect abdominal organs by comparing MV with spontaneous breathing and prone with supine position. All the studies were conducted using a porcine model. In three studies, a septic-like status was generated with an infusion of endotoxin; while in one study, a VILI model was used to simulate ARDS.In the first two studies, perfusion and lymphatic drainage were modified in different groups of animals and the impact of the changes on the abdominal organs was assessed. In the other two studies the effect of different ventilation settings on the abdominal organs was investigated: in Paper III, spontaneous breathing(CPAP) was compared with MV (maintaining positive end expiratory pressure – PEEP – and respiratory rate similar in both groups), and, in Paper IV, MV in prone position was compared with MV in supine position. The main findings were that low perfusion increased inflammation in the abdominal organs, but the hemodynamic parameters could not affect intestinal perfusion or edema. Similarly, increased edema was not associated with a decreased perfusion, but it enhanced inflammation in duodenum. MV increased systemic inflammation compared to CPAP, but did not increased inflammation or edema in the abdominal organs. Prone position reduced renal perfusion and was associated to extensive renal micro-thrombosis. In conclusion, both perfusion and edema influence inflammation in the abdomen, even if they seem not to affect one another. Besides, spontaneous breathing develops less systemic inflammation compared to MV, but it was not associated to a lower edema or inflammation in the abdomen; on the other side, prone positioning resulted in a possibly dangerous decrease of renal perfusion