ARDS Esophageal Balloon Pressure Changes With Positioning Study

The use of esophageal balloon catheters, which use esophageal pressure as a surrogate measurement for transpleural pressure, shows promise in improving outcomes of patients with severe acute respiratory distress syndrome (ARDS) requiring mechanical ventilator. The investigators hope to measure changes in in transpleural pressures in patients undergoing treatment with mechanical ventilation while switching from the supine, upright (head of bed \>30 degrees), and prone positions. The goal will be to measure the changes in chest wall and lung compliance in mechanically ventilated patients with changes in position.