**1. Introduction**

Acute respiratory distress syndrome (ARDS) consists of multiple underlying disease pathways and patterns of lung injury. When these progress to acute critical illness, all converge on the development of non-cardiogenic pulmonary edema [1]. CT chest imaging studies of ARDS patients have revealed that the amount of inflammatory pulmonary edema fluid correlates with gravity-dependent alveolar collapse [2, 3]. The sterno-vertebral distribution of aeration versus alveolar collapse during ARDS is the key to understanding the mechanisms of lung protective ventilatory strategies including low tidal volume ventilation, prone positioning, neuromuscular blockade, and, in the most severe cases, extracorporeal membrane oxygenation (ECMO).
