How does a severe crush injury lead to ards?

Inflammation. Patients who are critically ill get inflammation throughout the body that affects multiple organs. When the lung is affected it becomes filled with fluid, stiff and has difficulty doing its job of getting oxygen into the body, and carbon dioxide ( our waste gas) out. This is called ards.. In traumatic injuries/ crush, material leaked from the damaged tissue can act as the inflammatory trigger.
SIRS. Crush injuries start the inflammatory cascade that leads to a cytokine storm throughout the body; it is not clear which mediator is more important in crush syndrome leading to ards, but tissue ischemia or necrosis are necessary before you will see ards. The inflammatory cascade usually does not just injure the lungs, but the heart, liver, and kidneys are often affected as well.
Local muscle injury. Direct pressure on muscle cells: the direct pressure of the crush injury causes the muscle cells to become ischemic. The cells then switch to anaerobic metabolism, generating large amounts of lactic acid. Prolonged ischemia then causes the cell membranes to leak. Muscle can only withstand 4 hours ischemia ( without blood), there is also direct pressure due to crush (earth quakes).