Adaptive Support Ventilation in Acute Respiratory Distress Syndrome (ARDS)

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.

Adaptive Support Ventilation, ARDS, Esophageal Pressure, Mechanical Ventilation, Transpulmonary Pressure

Patients in this arm will have the ventilator adjusted per results of recent arterial blood gas. Esophageal balloon placement will be confirmed. Study team will measure several tidal breaths, end-expiratory and end-inspiratory ventilator holds. Then PEEP will be adjusted to achieve desired end-expiratory transpulmonary pressures, Fraction of Inspired Oxygen (FiO2) adjusted as needed to achieve SpO2>95%, and Tidal Volume (Vt) adjusted to 6cc/kg (IBW). Respiratory Rate (RR) will be adjusted to target the same minute ventilation achieved prior to any change in Vt. Patients will then be switched to ASV mode. The percentage minute volume (%minVol) will be adjusted to target the same minute ventilation as was achieved before the change. Settings will be maintained for approximately 1-2 hours, after which breath hold measurements will be repeated and another blood gas drawn.

Patients in this arm will have the ventilator adjusted per results of recent arterial blood gas. Esophageal balloon placement will be confirmed. Study team will measure several tidal breaths, end-expiratory and end-inspiratory ventilator holds. Then PEEP will be adjusted to achieve desired end-expiratory transpulmonary pressures, Fraction of Inspired Oxygen (FiO2) adjusted as needed to achieve SpO2>95%, and Tidal Volume (Vt) adjusted to 6cc/kg (IBW). Respiratory Rate (RR) will be adjusted (while leaving the Vt at 6cc/kg) to achieve the same minute ventilation. Patients will then be maintained on their current lung protective ventilation settings for approximately 1-2 hours, after which breath hold measurements will be repeated and another blood gas drawn.

Inclusion Criteria: Patients ≥ 18 years of age Receiving mechanical ventilation in an intensive care unit ARDS, as defined by the Berlin definition: Hypoxemic respiratory failure with PaO2 / FiO2 ratio < 300 mmHg Bilateral alveolar/interstitial infiltrates on chest x-ray, with opacities not present for more than 7 days Respiratory failure not fully explained by cardiac failure or fluid overload Intubation on mechanical ventilation and receiving PEEP ≥ 5 cm H2O Receiving mechanical ventilation from a Hamilton ventilator, on a controlled mode of ventilation. Exclusion Criteria: Clinical team refusal Esophageal injury or contraindication precluding placement of the esophageal balloon