MMP9 and acute respiratory distress syndrome: At 48 hours of intubation and ARDS onset, increasing active MMP-9 levels and fraction of active MMP-9 (active MMP-9/total MMP-9) had strong positive correlation (r = 0.75; p<0.001 and 0.61; p<0.001, respectively) with the need for prolonged mechanical ventilation in the ARDS subjects.