In 1967, Ashbaugh and colleagues first described acute respiratory distress syndrome (ARDS) - an acute illness, characterised by tachypnoea, hypoxaemia and loss of lung compliance occurring after a variety of pulmonary and non-pulmonary insults (including trauma, acute pancreatitis, viral pneumonitis)1. This concept is retained as the ARDS illness model within the current consensus definitions, with acute defined as within 7 days of insult, and hypoxaemia categorised using partial pressure of oxygen/fraction of inspired oxygen concentration (PaO2/FiO2 ratio) into mild (<40Kpa) , moderate (13.3-26.6Kpa) and severe (<=13.3Kpa) ARDS on a positive end expiratory pressure of >5 cm water2.