Spontaneous breathing and mechanical energy in assisted ventilation: Balancing benefits and risk

Spontaneous breathing during assisted mechanical ventilation may preserve diaphragm activity, improve ventilation–perfusion matching, reduce sedation requirements, and facilitate weaning, but excessive inspiratory effort can also increase transpulmonary pressure swings, promote pendelluft, worsen patient–ventilator asynchrony, and amplify injurious mechanical energy transfer. This narrative review summarizes current evidence on how spontaneous breathing can be integrated safely into assisted ventilation by balancing its physiological benefits against the risks of patient self-inflicted lung injury and ventilator-induced lung injury. Evidence from clinical, physiological, computational, and guideline-based studies was synthesized across domains related to respiratory effort, mechanical power, monitoring, and ventilatory strategy. Mechanical power provides a useful framework for understanding ventilatory energy delivery, but in assisted ventilation it should be interpreted together with patient-generated effort, transpulmonary pressure, and regional lung mechanics. Monitoring approaches such as oesophageal manometry, electrical impedance tomography, waveform analysis, and automated algorithms may help identify excessive effort and dyssynchrony. Proportional, adaptive, and flow-controlled ventilation strategies may better match assistance to patient demand and reduce unnecessary energy delivery. Overall, spontaneous breathing during assisted ventilation should not be regarded as uniformly beneficial or harmful; instead, integrating effort monitoring with mechanical-power-aware ventilation may support more individualized, energy-efficient, and safer assisted ventilation.