Unresolved ARDS is defined by the persistence of ARDS criteria at the end of the first week of evolution despite an appropriate treatment of the cause of ARDS. A persistent ARDS is associated with an increased mortality and prolonged lengths of mechanical ventilation, ICU stay and hospitalization. Persistent ARDS is characterized by ongoing inflammation, parenchymal-cell proliferation, and fibroproliferation leading to disordered deposition of collagen. All of these pathways may be responsive to corticosteroid therapy.