Ventilator-induced lung injury : The anatomical and physiological framework

Since its introduction in the treatment of the Acute Respiratory Distress Syndrome, mechanical ventilation has been so strongly interwoven with its side effects that someone started to consider it as invariably dangerous. Over the decades, attention has shifted from gross barotrauma to volutrauma and, more recently, atelectrauma and biotrauma. In this manuscript, we will describe the anatomical and physiological framework in which Ventilator-Induced Lung Injury (VILI) may occur. We will address the concept of lung stress/strain as applied to the whole lung or specific pulmonary regions. We will challenge some of the common beliefs, such as the claim of studying separately the dangerous effects of different tidal volumes (end-inspiration) and end-expiratory positive pressures (PEEP). Based on available data, we will suggest that stress at rupture is only rarely reached and that high tidal volume induces VILI by augmenting the pressure heterogeneity at the interface between open and constantly closed units. We believe that VILI occurs only when a given threshold is exceeded; below this limit, mechanical ventilation is likely to be safe.