Lung injury does not aggravate mechanical ventilation-induced early cerebral inflammation or apoptosis in an animal model

INTRODUCTION: The acute respiratory distress syndrome is not only associated with a high mortality, but also goes along with cognitive impairment in survivors. The cause for this cognitive impairment is still not clear. One possible mechanism could be cerebral inflammation as result of a “lung-brain-crosstalk”. Even mechanical ventilation itself can induce cerebral inflammation. We hypothesized, that an acute lung injury aggravates the cerebral inflammation induced by mechanical ventilation itself and leads to neuronal damage. METHODS: After approval of the institutional and state animal care committee 20 pigs were randomized to one of three groups: lung injury by central venous injection of oleic acid (n = 8), lung injury by bronchoalveolar lavage in combination with one hour of injurious ventilation (n = 8) or control (n = 6). Brain tissue of four native animals from a different study served as native group. For six hours all animals were ventilated with a tidal volume of 7 ml kg(-1) and a scheme for positive end-expiratory pressure and inspired oxygen fraction, which was adapted from the ARDS network tables. Afterwards the animals were killed and the brains were harvested for histological (number of neurons and microglia) and molecular biologic (TNFalpha, IL-1beta, and IL-6) examinations. RESULTS: There was no difference in the number of neurons or microglia cells between the groups. TNFalpha was significantly higher in all groups compared to native (p < 0.05), IL-6 was only increased in the lavage group compared to native (p < 0.05), IL-1beta showed no difference between the groups. DISCUSSION: With our data we can confirm earlier results, that mechanical ventilation itself seems to trigger cerebral inflammation. This is not aggravated by acute lung injury, at least not within the first 6 hours after onset. Nevertheless, it seems too early to dismiss the idea of lung-injury induced cerebral inflammation, as 6 hours might be just not enough time to see any profound effect.