Early Switch in Moderate ARDS

The optimal timing for transition from controlled to assisted mechanical ventilation in patients with acute respiratory distress syndrome (ARDS) remains uncertain. Excessive spontaneous respiratory effort may promote injurious transpulmonary pressure swings and heterogeneous regional ventilation, whereas unnecessary prolongation of controlled ventilation may increase sedation exposure and diaphragmatic dysfunction. This prospective, single-center physiological interventional study will enroll mechanically ventilated adults with ARDS and a PaO₂/FiO₂ ratio \>100 and ≤200 mmHg, measured during PEEP=5 cmH2O, who are receiving controlled mechanical ventilation. Participants will undergo a protocolized 30-minute transition from controlled to assisted mechanical ventilation after reduction of sedation sufficient to allow spontaneous respiratory activity. Respiratory effort and drive, airway and esophageal pressures, respiratory flow, respiratory mechanics, gas exchange, and regional ventilation measured by electrical impedance tomography will be assessed before and during the transition. Participants will subsequently be followed for 48 hours to determine whether assisted ventilation can be maintained without return to fully controlled mechanical ventilation.

Inclusion Criteria: * Age ≥18 years * Endotracheally intubated and receiving invasive mechanical ventilation * Meets diagnostic criteria for acute respiratory distress syndrome * PaO₂/FiO₂ ratio \>100 and ≤200 mmHg * Receiving controlled mechanical ventilation immediately before the transition trial Exclusion Criteria: * Implanted electrical cardiac or other device incompatible with electrical impedance tomography * Thoracic drains, extensive dressings, or other factors preventing appropriate EIT belt placement * Contraindication to placement of an esophageal balloon catheter * Active neuromuscular blockade at initiation of the transition trial * Significant hemodynamic instability * Any clinical condition for which reduction of sedation or transition to assisted ventilation is considered unsafe by the treating physician