The purpose of this protocol is to compare standard of care lung protective ventilation settings with an automated ventilator setting, called Adaptive Support Ventilation (ASV), in patients with acute respiratory distress syndrome (ARDS). This study will compare measurements (i.e. tidal volumes, driving pressure, respiratory rate (RR), compliance, peak airway pressures, plateau pressures, PEEP) with each ventilator technique, and will measure esophageal pressures to compare transpulmonary and respiratory system mechanics.

This study will compare two different modes of mechanical ventilation: standard lung protective controlled mandatory ventilation and Adaptive Support Ventilation. The investigators will enroll adult patients with ARDS who are mechanically ventilated and admitted to intensive care units, capturing a population with respiratory failure and significant critical illness. Patient mechanics during each ventilation strategy will be compared before and after crossover.

After obtaining informed consent, the investigators will place an esophageal balloon which will be used for simultaneous measurements of airway pressures (Pao) and esophageal pressures (Pes), to estimate transpulmonary pressures (PL = Pao - Pes), while also measuring Flow and Volume. Use of esophageal balloon catheters is common practice in the ICUs, and standard of care at Beth Israel Deaconess Medical Center is to use these balloons in patients with ARDS. Both the respiratory therapy and physician staff are very comfortable with placement and use. The esophageal balloon will be left in place until extubation. If the balloon is dislodged or removed for clinical purposes, it will not be replaced solely for research purposes unless it occurs on the first day of study measurements.

Patients will then be randomized to be switched to ASV immediately or to be maintained on their current lung protective ventilation settings.

Inclusion Criteria:

1. Patients ≥ 18 years of age

2. Receiving mechanical ventilation in an intensive care unit

3. ARDS, as defined by the Berlin definition:

   1. Hypoxemic respiratory failure with PaO2 / FiO2 ratio < 300 mmHg
   2. Bilateral alveolar/interstitial infiltrates on chest x-ray, with opacities not present for more than 7 days
   3. Respiratory failure not fully explained by cardiac failure or fluid overload
   4. Intubation on mechanical ventilation and receiving PEEP ≥ 5 cm H2O

4. Receiving mechanical ventilation from a Hamilton ventilator, on a controlled mode of ventilation.

Exclusion Criteria:

1. Clinical team refusal
2. Esophageal injury or contraindication precluding placement of the esophageal balloon