ALI biomarkers: Ventilator Induced Lung Injury experimental models and observational clinical studies. High tidal volume ventilation (tidal volume in excess of 10 ml/kg predicted body weight) may be used to induce lung injury in experimental models (left) but, through the overspill of inflammatory mediators into the circulation (biotrauma), multiple-organ dysfunction may follow. Biomarkers may be assayed directly from the lungs (black), from the circulation (red) or as indices of dysfunction related to other organs (green). In clinical studies (right), injured lungs are susceptible to damage even when gold standard mechanical ventilation (tidal volume 6 ml/kg predicted body weight) is used. However, in the presence of existing lung injury several processes are likely to be concurrent, both affecting the lungs directly (inflammation, tissue injury, coagulation, fibrosis) and indirectly from other affected organs (sepsis). Hence, the relationship between any biomarker and ventilator settings is likely to be obscured by multiple unknowns. BAL bronchoalveolar lavage, SIRS systemic inflammatory response syndrome, MODS multiple organ dysfunction syndrome.