Hyperoxia provokes a time- and dose-dependent inflammatory response in mechanically ventilated mice, irrespective of tidal volumes.

Background: Mechanical ventilation and hyperoxia have the potential to independently promote lung injury and inflammation. Our purpose was to study both time- and dose-dependent effects of supplemental oxygen in an experimental model of mechanically ventilated mice.

Methods: Healthy male C57Bl/6J mice, aged 9-10 weeks, were intraperitoneally anesthetized and randomly assigned to the mechanically ventilated group or the control group. In total, 100 mice were tracheotomized and mechanically ventilated for either 8 or 12 h after allocation to different settings for the applied fractions of inspired oxygen (FiO, 30, 50, or 90%) and tidal volumes (7.5 or 15 ml/kg). After euthanisation arterial blood, bronchoalveolar lavage fluid (BALf) and tissues were collected for analyses.

Results: Mechanical ventilation significantly increased the lung injury score (P < 0.05), mean protein content (P < 0.001), and the mean number of cells (P < 0.01), including neutrophils in BALf (P < 0.001). In mice ventilated for 12 h, a significant increase in TNF-α, IFN-γ, IL-1β, IL-10, and MCP-1 (P < 0.01) was observed with 90% FiO, whereas IL-6 showed a decreasing trend (P for trend = 0.03) across FiO groups. KC, MIP-2, and sRAGE were similar between FiO groups. HMGB-1 was significantly higher in BALf of mechanically ventilated mice compared to controls and showed a gradual increase in expression with increasing FiO. Cytokine and chemokine levels in BALf did not markedly differ between FiO groups after 8 h of ventilation. Differences between the tidal volume groups were small and did not appear to significantly interact with the oxygen levels.

Conclusions: We demonstrated a severe vascular leakage and a pro-inflammatory pulmonary response in mechanically ventilated mice, which was enhanced by severe hyperoxia and longer duration of mechanical ventilation. Prolonged ventilation with high oxygen concentrations induced a time-dependent immune response characterized by elevated levels of neutrophils, cytokines, and chemokines in the pulmonary compartment.