MPO and acute respiratory distress syndrome: In the control non-ARDS group, no correlation was observed between the tracheal aspirate biomarkers (active MMP-9, total MMP-9, percent active MMP-9, MMP-8, TIMP-1, MMP-9:TIMP-1, HNE and MPO) and clinical markers of disease severity and outcome measures (P/F ratios, OI, PRISM 12, PRISM 24, MOSF, duration of intubation and VFDs).