Assessment of Respiratory Drive and Inspiratory Effort Across Pressure Support Levels in Patients After Major Abdominal Surgery

Inclusion Criteria: * Adult patients (≥18 years) admitted to the surgical ICU * Recent major abdominal surgery (intra-peritoneal operation without primary thoracic involvement, including luminal resection and/or resection of a gastrointestinal solid organ) requiring postoperative ICU care * Receiving invasive mechanical ventilation in pressure support ventilation (PSV) mode at the time of enrollment * Duration of invasive mechanical ventilation \>48 hours * Clinically stable, with no plan for extubation within 6 hours of study enrollment, defined by all of the following: Respiratory rate \<35 breaths/min, SpO₂ ≥90%, Heart rate \<140 bpm, No visible accessory muscle use, Hemodynamically stable without escalation of vasopressor support during the past hour, Able to tolerate short-term adjustments in PSV level as per protocol Exclusion Criteria: * Known neuromuscular disease affecting respiratory muscle function * Hemodynamic instability requiring escalation of vasopressor support * Severe hypoxemic respiratory failure requiring Positive End-Expiratory Pressure (PEEP) \>10 cmH₂O or FiO₂ \>60% * Deep sedation (Richmond Agitation-Sedation Scale \[RASS\] score \< -3) or ongoing neuromuscular blockade * History of chronic obstructive pulmonary disease (COPD) or other obstructive lung disease