Physiological Effects of Controlled vs. Assisted Ventilation During Moderate-to-severe ARDS (PEARL Study)

Background: In patients with acute hypoxemic respiratory failure or ARDS, mechanical ventilation is often required. Two common strategies are pressure support ventilation (PSV), which allows spontaneous breathing, and volume-controlled ventilation (VCV), which delivers fixed tidal volumes. Although PSV can improve comfort, strong inspiratory efforts may cause excessive lung inflation and increase the risk of ventilator-induced lung injury (VILI). In contrast, VCV with muscle paralysis ensures full control over tidal volume and driving pressure, potentially offering better lung protection. Hypothesis: The study will help determine whether a controlled ventilation strategy - with or without volume adjustments and with or without muscle paralysis - provides superior lung protection compared to PSV in hypoxemic patients with intense inspiratory effort. Methods: This prospective physiological study will be performed in the ICU of Fondazione Policlinico Universitario A. Gemelli (Rome, Italy) and will include 20 moderate to severe ARDS patients. Each patient will undergo four 30-minute ventilation phases: PSV with clinical PEEP; VCV at 6 ml/kg predicted body weight (PBW); VCV with muscle paralysis and Vt equal to PSV; VCV with muscle paralysis and Vt adjusted to keep driving pressure ≤14 cmH₂O. During each phase, data on gas exchange, respiratory mechanics, inspiratory effort, and regional ventilation (via electrical impedance tomography) will be collected. Endpoints: Primary: Regional tidal volume distribution during VCV vs. PSV. Secondary: Transpulmonary driving pressure, dorsal ventilation fraction, and pendelluft occurrence. Expected Impact: By comparing assisted and controlled ventilation under different conditions, the study aims to clarify which strategy better balances patient comfort, effective ventilation, and lung protection in ARDS patients with high respiratory drive.