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

Background and RationaleInvasive mechanical ventilation is often necessary in critically ill adults but may contribute to ventilator-induced lung injury (VILI) if ventilator settings are not individualized. During assisted ventilation (pressure support ventilation, PSV), ongoing patient effort complicates the assessment of PEEP response, PEEP titration, and lung recruitability.Ventilator-delivered sigh breaths (i.e., brief sustained inflations) can improve gas exchange and promote alveolar recruitment, and may permit artifact-free assessment of respiratory mechanics in assisted modes. This study evaluates whether Crs measured at the end of a sigh provides reliable, clinically useful information on recruitability and whether the ratio of Crs during sigh to Crs during an assisted breath (Crs_sigh/Crs_assisted) can guide positive end-expiratory pressure (PEEP) optimization.Primary ObjectiveTo assess lung recruitability during PSV by normalizing Crs measured at the end of a sigh to Crs obtained with an inspiratory hold during an assisted breath.Secondary Objectives

• To quantify the proportion of patients in whom Pplat during assisted breathing is not reliable (non-readable or unstable ≥3 s).
• To determine whether adjusting PEEP according to the sigh-derived recruitability index improves Crs.

Inclusion criteria:Adults (≥18 years) receiving PSV with the ventilator's sigh function active.Exclusion criteria:

• Clinical contraindication to increasing PEEP
• Hemodynamic instability defined as SOFA cardiovascular score ≥3

Protocol OverviewEach participant undergoes two sequential, non-randomized steps: