Monitoring respiratory mechanics during assisted ventilation

Accurate monitoring of the mechanical properties of the respiratory system is crucial to understand the pathophysiological mechanisms of respiratory failure in mechanically ventilated patients, to optimize mechanical ventilation settings and to reduce ventilator-induced lung injury. However, although the assessment of respiratory mechanics is simple in patients undergoing fully controlled ventilation, it becomes quite challenging in the presence of spontaneous breathing activity. Aim of the present review is to describe how the different components of respiratory mechanics [resistance, static compliance, and intrinsic positive end-expiratory pressure (PEEP)] can be measured at the bedside during assisted modes of ventilation.

Available techniques for bedside measurement of resistance during assisted ventilation are complex and not commonly implemented. On the contrary, an increasing number of reports indicate that measurement of static compliance and intrinsic PEEP can be easily obtained, both with advanced monitoring systems (esophageal and gastric manometry, diaphragm electromyography, electrical impedance tomography) and, with some limitations, with simple airways occlusion maneuvers.

Assessment of respiratory mechanics in spontaneously breathing patients, with some limitations, is feasible and should be included in everyday clinical practice; however, more data are needed to understand the clinical relevance of the measures obtained during assisted ventilation.