Sigh in Pressure Support Ventilation to Detect Respiratory System Compliance and Lung Recruitability

Each patient undergoes two sequential 15-minute steps: 1) pressure support ventilation at the clinical PEEP and 2) the same settings with PEEP increased by 3 cmH₂O. A ventilator-delivered sigh is programmed as one sustained inflation at 30 cmH₂O for 3 seconds every minute. All other ventilator parameters (trigger sensitivity, pressure support level, mandatory breath timing) remain unchanged. At the end of each step, inspiratory and expiratory holds are performed to collect respiratory mechanics and arterial blood gases; compliance during the sigh is calculated once flow is zero and airway pressure is stable.