Do more injured lungs need more protection? Let’s test it

Driving pressure, calculated as the difference between plateau pressure and positive end-expiratory pressure (PEEP) during mechanical ventilation in a relaxed subject, has an independent association with the risk of death in patients with acute respiratory distress syndrome (ARDS) (1, 2), suggesting that interventions in these patients such as PEEP titration are beneficial only if associated with a decrease in driving pressure. Lung computed tomography demonstrating heterogonous aeration in ARDS typically reveals dependent nonaerated lung, which is central to both our current understanding of ventilation strategies (3) and the typical increase in respiratory system stiffness (static elastance) estimated as the driving pressure divided by the Vt. Perhaps readers will be more familiar with compliance (the inverse of elastance); both static respiratory system elastance and compliance are largely influenced by the volume of aerated lung. As both the stress and strain resulting in ventilation-induced lung injury reflect Vt and end-expiratory lung volume, targeting driving pressure makes sense, as driving pressure, in effect, scales Vt to the magnitude of the reduced lung volume for a given patient with ARDS.