End-Expiratory Diaphragmatic Residual Contraction Index for Identifying Intrinsic PEEP and Assisting PEEP Titration: A Prospective Physiological Study

Inclusion Criteria: * Age ≥ 18 years. Patients receiving invasive mechanical ventilation in Pressure Support Ventilation (PSV) mode. Clinically assessed as having a risk of dynamic intrinsic PEEP (PEEPi,dyn) or experiencing difficult weaning from mechanical ventilation. Presence of an indwelling esophageal balloon catheter (for reference standard measurements). Provision of written informed consent from the patient or legally authorized representative. Exclusion Criteria: * Pregnancy or lactation. Known esophageal diseases (e.g., esophageal varices, strictures, recent esophageal surgery) or contraindications to esophageal catheter placement. Severe hemodynamic instability (e.g., requiring high-dose vasoactive support, uncontrolled arrhythmias). Severe hypoxemia (PaO2/FiO2 \< 100 mmHg) or severe hypercapnia with hemodynamic compromise at baseline. Conditions precluding ultrasound assessment of the diaphragm (e.g., extensive chest wall trauma, large pleural effusion, severe subcutaneous emphysema). Active spontaneous breathing with severe patient-ventilator asynchrony that cannot be stabilized during the trial. Anticipated extubation or withdrawal of life-sustaining treatment within the next 24 hours. Participation in another interventional clinical trial within the last 30 days.