Pressure Release Ventilation Compared to Lung Protective Ventilation in Moderate and Severe ARDS

Acute respiratory distress syndrome (ARDS) is a severe form of acute respiratory failure characterized by impaired oxygenation and bilateral pulmonary abnormalities. Mechanical ventilation is a cornerstone of supportive treatment for patients with moderate to severe ARDS.

This prospective randomized controlled study compares airway pressure release ventilation (APRV) with conventional low-tidal-volume ventilation (LTV) in patients with moderate to severe ARDS. Eligible patients are randomly allocated in a 1:1 ratio to receive either APRV or LTV according to a predefined ventilation protocol.

In the LTV group, ventilation is provided using a lung-protective strategy with tidal volumes targeted according to predicted body weight and limitation of plateau pressure. In the APRV group, ventilation is delivered using two airway pressure levels with prolonged high-pressure periods and brief release periods. APRV settings are individualized according to oxygenation, ventilation, respiratory mechanics, clinical response, and hemodynamic tolerance. Release tidal volume, minute ventilation, and respiratory-system compliance are monitored during APRV.

Patients in both groups undergo daily assessment for readiness for ventilator weaning. Once predefined weaning criteria are met, patients undergo a standardized spontaneous breathing trial using the same procedure in both groups. Patients who successfully complete the trial are assessed for extubation according to predefined clinical criteria.

The primary outcome is successful extubation, defined as liberation from invasive mechanical ventilation without the need for reintubation within 72 hours after extubation. Secondary outcomes include time to successful extubation, duration of mechanical ventilation, change in the PaO₂/FiO₂ ratio during the first 7 days, ICU length of stay, and hospital length of stay. Safety outcomes include all-cause mortality and barotrauma.

Inclusion criteria

• Adult patients aged 18 years or older.
• Mechanically ventilated patients admitted to the Intensive Care Unit (ICU) at Banha University Hospital.
• Patients diagnosed with moderate-to-severe acute respiratory distress syndrome (ARDS) according to the 2023 European Society of Intensive Care Medicine (ESICM) guidelines, characterized by (Matthay et al., 2024):

• An acute predisposing risk factor (e.g., pneumonia, non-pulmonary infection, trauma, transfusion, aspiration, or shock), with pulmonary edema not primarily attributable to cardiogenic causes or fluid overload.
• Acute onset or worsening of hypoxemic respiratory failure within one week of the onset of the predisposing risk factor or new/worsening respiratory symptoms.
• Bilateral pulmonary opacities on chest radiography, computed tomography, or lung ultrasound that are not fully explained by pleural effusions, atelectasis, or pulmonary nodules/masses.
• Moderate ARDS defined as a PaO₂/FiO₂ ratio >100 to ≤200 mmHg (or SpO₂/FiO₂ ratio >148 to ≤235 when SpO₂ <97%) or severe ARDS defined as a PaO₂/FiO₂ ratio ≤100 mmHg (or SpO₂/FiO₂ ratio ≤148).

Exclusion criteria

• Patients younger than 18 years of age.
• Pregnant women.
• Patients with severe chronic heart failure (New York Heart Association Class III or IV).
• Patients with uncontrolled shock requiring escalating doses of vasopressor support.
• Patients with severe cardiac arrhythmias or active myocardial ischemia.