V/Q Matching in Pressure Support Ventilation

Spontaneous breathing during mechanical ventilation has been attributed to both protective and negative effects on patient outcomes, largely varying based on the severity of lung injury. Indeed, in severe ARDS the avoidance of spontaneous efforts has an established protective role. However, spontaneous breathing promotes the distribution of tidal volume towards the dependent lung, and low levels of support pressure determine more homogeneous ventilation in patients recovering from ARDS, compared to higher support levels. Physiology supports the potential of spontaneous breathing to increase lung perfusion, through the decrease of intra-thoracic pressure leading to an increased venous return. This mechanism, in absence of right ventricular dysfunction, may lead to increased global lung perfusion. Furthermore, gas exchange improvements in experimental lung injury models during pressure support vs. controlled ventilation have been explained with redistribution of lung perfusion to nondependent lung areas and improvement of V/Q matching even in absence of significant lung recruitment. Electrical impedance tomography has been clinically used as a non-invasive tool to assess V/Q matching in patients with ARDS and to compare V/Q matching prior to and after a cycle of prone position in spontaneously breathing patients with COVID-19. The aim of this study is to describe the effects of different levels of pressure support on ventilation-perfusion matching in patients recovering from ARDS, using electrical impedance tomography.