Inflammation and Lung Injury in an Ovine Model of Extracorporeal Membrane Oxygenation Support

Extracorporeal membrane oxygenation (ECMO) is a life-saving treatment for patients with severe, refractory, cardiorespiratory failure. Exposure to the ECMO circuit is thought to trigger/exacerbate inflammation. Determining whether inflammation is due to the patients underlying pathologies or the ECMO circuit is difficult. To discern how different insults contribute to the inflammatory response we developed an ovine model of lung injury and ECMO to investigate the impact of smoke-induced lung injury and ECMO in isolation and cumulatively on pulmonary and circulating inflammatory cells, cytokines and tissue remodeling. Sheep receiving either smoke-induced acute lung injury (S-ALI) or sham injury were placed on veno-venous (VV) ECMO lasting either 2 or 24hrs, with controls receiving conventional ventilation only. Lung tissue, bronchoalveolar fluid and plasma were analyzed by RT-PCR, immunohistochemical staining and zymography to assess inflammatory cells, cytokines and matrix metalloproteinases. Pulmonary compliance decreased in sheep with S-ALI placed on ECMO with increased numbers of infiltrating neutrophils, monocytes and alveolar macrophages compared to controls. Infiltration of neutrophils was also observed with S-ALI alone. RT-PCR studies showed higher expression of MMP2 and MMP9 in S-ALI plus ECMO while IL-6 was elevated at 2hrs. Zymography revealed higher levels of MMP2. Circulating plasma levels of IL-6 were elevated 1-2hrs after commencement of ECMO alone. This data shows that the inflammatory response is enhanced when a host with pre-existing pulmonary injury is placed on ECMO, with increased infiltration of neutrophils and macrophages, the release of inflammatory cytokines and up regulation of matrix metalloproteinases