Mechanical ventilation increases the inflammatory response induced by lung contusion.

ABSTRACT

BACKGROUND: Posttraumatic lung contusion is common after blunt chest trauma, and patients often need ventilatory support. Lung contusion induces an inflammatory response signified by primed polymorph neutrophil granulocytes (PMNs) in blood and tissue. Mechanical ventilation (MV) can also cause an inflammatory response. The aim of this study was to develop an animal model to investigate the effect of high-volume ventilation on the inflammatory response in blunt chest trauma. MATERIALS AND METHODS: We assigned 23 male Sprague-Dawley rats to either MV or bilateral lung contusion followed by MV. We used three extra rats as controls. Lung contusion was induced by a blast generator, a device releasing a single pressure blast wave centered on the chest. We determined tissue and systemic inflammation by absolute PMN numbers in blood and bronchoalveolar lavage fluid (BALF), myeloperoxidase, interleukin (IL)-6, IL 1ß, growth-related oncogene-KC, and IL-10 in both plasma and BALF. RESULTS: Survival after blunt chest trauma was correlated to the distance to the blast generator. Compared with controls, both MV and blast plus MV rats showed increased systemic and pulmonary inflammation, expressed by higher PMNs, myeloperoxidase levels, and cytokine levels in both blood and BALF. Blast plus MV rats showed a higher systemic and pulmonary inflammatory response than MV rats. CONCLUSIONS: The blast generator generated reproducible blunt chest trauma in rats. Mechanical ventilation after lung contusion induced a larger overall inflammatory response than MV alone, which indicates that local damage contributes not only to local inflammation, but also to systemic inflammation. This emphasizes the importance of lung protective ventilation strategies after pulmonary contusion.