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

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

This physiological observational study will assess respiratory drive and inspiratory effort across varying levels of pressure support ventilation (PSV) in adult surgical ICU (SICU) patients after major abdominal surgery. By using non-invasive bedside indices (airway occlusion pressure at 100 ms after the onset of inspiration [P0.1], maximum negative occlusion pressure [Pocc], and pressure muscle index [PMI]), we aim to quantify how patients adapt to changes in ventilatory support and determine patterns of under- and over-assistance. Findings may inform optimal titration of PSV to reduce complications and improve clinical outcomes.

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