Expiratory Flow Bias and Physiological Effects of Rapid Chest Compression in Mechanically Ventilated Neurocritical Patients: A Secondary Analysis of a Randomized Controlled Trial

<b>Background:</b> Mechanical ventilation compromises airway clearance, with expiratory flow bias (EFB) being a critical determinant of mucus transport. The rapid chest compression technique (RCCT) generates high EFB, yet evidence in neurocritical patients is limited due to concerns regarding intracranial pressure (ICP). This secondary analysis of a randomized controlled trial examined the effects of RCCT on ventilatory mechanics and physiology in acute brain-injured patients under invasive ventilation. <b>Methods:</b> Fifty neurocritical patients were randomized to RCCT (Intervention) or passive leg mobilization (Control). RCCT was applied bilaterally during expiration once every three respiratory cycles for 5 min; controls underwent 5 min of passive cycling. EFB, derived from inspiratory and expiratory peak flows, was assessed at baseline (T-5), during intervention (T0-T5), and post-intervention (T+5, T+30). Arterial blood gases, mean arterial pressure (MAP), heart rate (HR), and ICP were also analyzed. Group comparisons used parametric/non-parametric tests; associations were explored via Spearman's rho. <b>Results:</b> Baseline EFB did not differ between groups. From T0 to T5, Intervention patients showed significantly higher EFB (all <i>p</i> < 0.001). PaCO₂ decreased within the Intervention group (<i>p</i> = 0.015) but not in controls (<i>p</i> = 0.601). No between-group ΔPaCO₂ differences emerged. At T5, HR correlated negatively with EFB (ρ = -0.49, <i>p</i> = 0.013). No associations were found with age, sex, lesion type, MAP, or ICP. <b>Conclusions:</b> RCCT effectively increased EFB in ventilated neurocritical patients without affecting ICP, supporting its safety and potential role in airway clearance.