Physiological and clinical effects of selected airway clearance techniques in mechanically ventilated adult ICU patients: a systematic review and synthesis without meta-analysis

Background and objectives: Secretion retention is common in invasively mechanically ventilated ICU patients. Airway clearance techniques (ACTs) are widely used, although their physiological and clinical effects remains uncertain. We aimed to evaluate the physiological and clinical effects of selected ACTs in invasively mechanically ventilated adult ICU patients. Methods: This systematic review was registered in PROSPERO (CRD42025631124) and conducted according to PRISMA guidelines. We searched MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials (CENTRAL), Web of Science, and PEDro up to 20 March 2025. Studies evaluating ventilator hyperinflation, PEEP-ZEEP technique, expiratory rib-cage compression (ERCC), or mechanical insufflation-exsufflation (MI-E) in mechanically ventilated adults were included. We assessed risk of bias using the Cochrane Risk of Bias tool for randomized studies and Joanna Briggs Institute tools for observational studies and case series. The primary outcome was secretion clearance (e.g., sputum weight or volume). Secondary outcomes included clinical outcomes (mortality, duration of invasive mechanical ventilation, ICU length of stay), safety (adverse events during ACTs), and respiratory complications related to impaired airway clearance (gas-exchange impairment, increased work of breathing, and ventilator-associated pneumonia). Results: Forty-six studies including 1,884 patients were analysed. Secretion clearance was the most frequently reported outcome. Several studies reported greater secretion clearance with ACTs compared with standard care or suctioning alone, although findings varied across techniques, comparisons, and outcome definitions. ERCC, MI-E, and hyperinflation techniques were associated with increased secretion clearance in some studies, whereas results for PEEP-ZEEP technique were inconsistent. Effects on respiratory mechanics, oxygenation, and clinical outcomes were variable and predominantly short-term. Clinically relevant respiratory complications and patient-centred outcomes were inconsistently reported. No clear effect was observed on mortality, duration of mechanical ventilation, or ICU length of stay. No major adverse events were reported. Conclusion: Selected ACTs may improve short-term secretion clearance in invasively ventilated ICU patients. However, the evidence is largely limited to surrogate physiological outcomes and is of low certainty for clinically meaningful outcomes, whose effects remain uncertain. Further high-quality studies using standardized outcome definitions and robust safety reporting are required.