JICS education: mechanical ventilation - physiology, mechanism and modes.

Mechanical ventilation remains a cornerstone of organ support in critically ill patients, yet modern intensive care ventilators incorporate increasingly complex modes and proprietary terminology that can obscure the physiological principles underpinning their use. A clear understanding of these principles is essential to enable safe, individualised, and lung protective ventilation. This article provides the physiological foundation for a four-part educational series on mechanical ventilation in adult critical care. Key concepts including positive end-expiratory pressure, airway pressures, resistance, compliance, elastance, and respiratory time constants are reviewed. Evidence supporting contemporary ventilation strategies is summarised, emphasising the importance of low tidal volume ventilation and individualisation of ventilator settings according to patient physiology. The ventilator breath cycle is described in terms of triggering, delivery, cycling, and expiration, providing a framework that is independent of manufacturer-specific nomenclature. A structured approach to ventilator modes based on control variables, breath sequence, and targeting schemes is presented using the Taxonomic Attribute Grouping system. Conventional pressure- and volume-controlled modes are discussed alongside assisted and mandatory ventilation strategies. Advanced modes, including airway pressure release ventilation and closed-loop systems, are reviewed with reference to their physiological rationale and current evidence base. Mechanical ventilation should be understood as a set of physiological principles rather than a collection of proprietary mode names. By focusing on pressure, flow, volume, timing, and patient-ventilator interaction, clinicians can better adapt ventilatory support to the changing pathophysiology of individual patients. This article aims to provide a practical framework for trainees and clinicians seeking to understand contemporary mechanical ventilation and to support subsequent articles addressing lung-protective ventilation, difficult weaning, and extracorporeal respiratory support.