Electrical Impedance Tomography for Monitoring Prone Positioning in ARDS

Prone positioning (PP) has evolved from an experimental maneuver into a cornerstone therapy for moderate-to-severe ARDS, supported by robust evidence of survival benefit. Its physiological rationale includes reducing dorsoventral mechanical heterogeneity, promoting dependent alveolar recruitment, improving ventilation-perfusion ($\dot{V}/\dot{Q}$) matching, and attenuating ventilator-induced lung injury (VILI). In preclinical models, PP also homogenizes the pleural pressure response to spontaneous breathing effort, thereby attenuating effort-dependent lung injury, a mechanism particularly relevant for awake PP. Despite these well-characterized mechanisms, the clinical response to PP is highly individualized, and a substantial proportion of patients do not show meaningful improvement in oxygenation. Furthermore, optimal PEEP during PP cannot be reliably inferred from conventional global monitoring parameters or from supine PEEP settings. Electrical impedance tomography (EIT) is a radiation-free, continuous bedside imaging tool that enables real-time spatial assessment of regional lung ventilation, perfusion, and alveolar recruitment. Applied during PP, EIT can directly visualize the redistribution of tidal ventilation toward dorsal lung regions, identify persistent collapse or overdistention, guide individualized PEEP titration, and quantify $\dot{V}/\dot{Q}$ matching, all of which are inaccessible from global metrics alone. This narrative review examines the physiological mechanisms of PP, the temporal dynamics of ventilation and perfusion responses, and the clinical heterogeneity of mechanical response. It evaluates the current evidence base for EIT as a tool to guide individualized ventilator management during PP in ARDS, distinguishing established findings from physiologically derived rationale and areas requiring future clinical validation. Clinical implications and future directions, including awake proning, serial sessions, and PP during extracorporeal membrane oxygenation, are also discussed.