Supplementary Material for: High-Frequency Chest Wall Oscillation in Critical Care: A Systematic Review

Background: Airway secretion retention represents a major clinical challenge in critically ill patients, promoting gas exchange impairment and atelectasis, precipitating failure of non-invasive respiratory support, and prolonging invasive mechanical ventilation, with an associated increase in respiratory-related complications and mortality. High-frequency chest wall oscillation (HFCWO) is a non-invasive airway clearance technique widely used in chronic respiratory diseases, but its role in the intensive care unit (ICU) remains unclear. This systematic review aims to evaluate the available evidence on the efficacy and safety of HFCWO in adult ICU patients. Methods: A systematic literature search was conducted in PubMed/MEDLINE, Embase, and Cochrane Library from inception to December 2025, in accordance with PRISMA guidelines. Studies evaluating HFCWO in adult ICU patients, including those receiving invasive or non-invasive respiratory support, were eligible. Primary outcomes included duration of mechanical ventilation, ICU length of stay, and mortality. Secondary outcomes included impact on secretion airway clearance and its radiographic/functional surrogates as well as safety and treatment tolerance. Results: A limited number of studies met the inclusion criteria, mainly small randomized controlled trials and observational studies, characterized by substantial heterogeneity in patient populations, intervention protocols, and assessed outcomes. HFCWO effects on clinically meaningful primary endpoints, including duration of mechanical ventilation, length of ICU stay, and mortality, remain variable and inconclusive. Overall, HFCWO was well tolerated and appeared to enhance secretion clearance, with some studies reporting modest improvements in oxygenation and respiratory mechanics. Conclusions: Current evidence suggests that HFCWO is a safe and feasible airway clearance strategy in selected ICU patients with secretion burden without proved effects on the main clinical ouctomes. However, robust data supporting its routine use to improve hard clinical outcomes are lacking. Well-designed, adequately powered randomized trials are needed to define patient selection criteria, optimal timing, and the true clinical impact of HFCWO in the ICU setting.