Acute respiratory distress syndrome (ARDS) is a severe lung condition that causes respiratory failure. Individuals with ARDS often require the use of an artificial breathing machine, known as a mechanical ventilator. High frequency oscillatory ventilation (HFOV) is a form of mechanical ventilation that pumps small amounts of air into the lungs at a constant high rate. The purpose of this study is to compare the safety and efficacy of two HFOV methods in individuals with ARDS.