 In 2012, an update of the ARDS definition The Berlin criteria was published and an empirical classification was proposed according to three PaO2FiO2 cut-off values at ARDS onset: severe 100 mmHg, moderate 100 - 200 mmHg, and mild 200 - 300 mmHg on positive end-expiratory pressure PEEP 5 cmH2O. However, despite that there is sufficient evidence about the interactions between PEEP and FiO2, these cut-off values did not mandate the assessment of hypoxemia under standardized guidelines. 