Although mechanical ventilation is life saving, it is associated with a number of severe complications collectively referred to as ventilator induced lung injury (VILI). VILI contributes to the high morbidity and mortality associated with the acute respiratory distress syndrome (ARDS). Within the context of a randomized study evaluating the feasibility of conducting a study comparing high frequency oscillation to conventional lung protective ventilation in early severe ARDS, we are evaluating the effect of both ventilator strategies on biological markers of VILI.