Continuous and noninvasive respiratory effort monitoring: a narrative review of emerging techniques

Ventilator-induced lung injury and diaphragm dysfunction are well-recognized complications of mechanical ventilation and commonly attributed to inadequate ventilator settings. Excessive or insufficient assistance and the patient's own respiratory effort are increasingly acknowledged as important factors in the pathogenesis of these injuries. Therefore, monitoring respiratory effort at the bedside is a highly relevant strategy to identify and prevent potentially injurious breathing patterns. Esophageal manometry remains the reference standard for assessing respiratory effort, but its technical complexity limits routine clinical use. Placement and calibration of the esophageal balloon are time-consuming and require specific expertise. Moreover, the invasive nature of the procedure precludes visual confirmation and leads to uncertainty about correct positioning, reducing confidence in the validity of measurements. Innovative noninvasive and continuous monitoring techniques are emerging as more accessible and scalable alternatives, enabling assessment of respiratory effort without impacting so much on clinical workflow. This narrative review provides an in-depth overview of three noninvasive techniques that are reshaping continuous respiratory effort monitoring: (1) Surface electromyography (sEMG) now enables continuous monitoring of respiratory muscle activity and derivation of continuous effort estimation using electrodes placed on the torso of the patient. (2) Computational modeling offers dynamic, patient-specific effort estimation from ventilator waveforms. (3) Assessment of diaphragm thickening fraction, derived from high-resolution ultrasound, provides a straightforward surrogate for effort, driven by widely available acquisition devices. Together, these innovations promise to make respiratory muscle monitoring less labor-intensive and more clinically sustainable-paving the way for broader implementation of diaphragm-protective ventilation strategies in critical care.