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.
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
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
Single group
Stepwise PSV adjustment protocol
Procedure/SurgeryPatients will undergo standardized stepwise PSV changes (baseline, ±3 cmH₂O, ±6 cmH₂O, return to baseline), with 2-minute stabilization and repeated measurements of ventilatory parameters.
Respiratory drive and inspiratory effort across pressure support levels
Respiratory drive and inspiratory effort will be assessed using airway occlusion pressure at 0.1 seconds (P0.1), maximum negative inspiratory occlusion pressure (Pocc), and the pressure muscle index (PMI). These indices are measured non-invasively via ventilator maneuvers during standardized stepwise adjustments of pressure support ventilation (baseline, ±3 cmH₂O, ±6 cmH₂O, return to baseline). The mean of three repeated measurements at each step will be analyzed.
Incidence of ventilatory response patterns during PSV
Ventilatory response patterns will be categorized as quasi-passive or active based on physiological criteria derived from changes in tidal volume, plateau pressure, and PMI during stepwise PSV adjustments. Patterns will be determined from individual response trends.
Duration of mechanical ventilation after protocol
Time from completion of the PSV protocol until successful extubation, measured in hours. Reintubation within 48 hours will be recorded separately.
Reintubation or non-invasive ventilation use
Proportion of patients requiring reintubation or initiation of non-invasive ventilation within 48 hours after extubation following study participation.
ICU length of stay
Total number of days from ICU admission to ICU discharge.
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Mahidol University
Lead sponsor
Siriraj Hospital
Collaborator
