ABSTRACT
Acute respiratory distress syndrome (ARDS) in adults is defined clinically by the rapid onset of noncardiogenic pulmonary edema in association with refractory hypoxemia. Since the initial description of ARDS, the defining criteria have been revised several times, most recently in Berlin, Germany, in 2012. This recent classification replaces the previously widely used American-European Consensus (AEC) clinical definition published in 1994, according to the level of oxygenation described by the ratio of the partial pressure of oxygen in the patient’s arterial blood (PaO2) to the fraction of oxygen in the inspired air (FIO2). In ARDS, the PaO2/FiO2 (P/F) ratio is less than 200, and in acute lung injury (ALI), it is less than 300. The AEC definition, although widely known, did not consider the relevance of the precipitating condition to prognosis, or standardize the strategy of mechanical ventilatory support to be used when hypoxemia is quantified. The Berlin definition (1) categorizes ARDS as mild, moderate, or severe according to the P/F ratio (Table 58.1); those with P/F ratio 200 to 300 now have mild ARDS, not acute lung injury (ALI); further differences include that the requirement to exclude heart failure is not essential; these conditions can, of course, coexist.
