A universal definition of ARDS: the PaO2/FiO2 ratio under a standard ventilatory setting-a prospective, multicenter validation study

The PaO2/FiO(2) is an integral part of the assessment of patients with acute respiratory distress syndrome (ARDS). The American-European Consensus Conference definition does not mandate any standardization procedure. We hypothesized that the use of PaO2/FiO(2) calculated under a standard ventilatory setting within 24 h of ARDS diagnosis allows a more clinically relevant ARDS classification. We studied 452 ARDS patients enrolled prospectively in two independent, multicenter cohorts treated with protective mechanical ventilation. At the time of ARDS diagnosis, patients had a PaO2/FiO(2) a parts per thousand currency sign 200. In the derivation cohort (n = 170), we measured PaO2/FiO(2) with two levels of positive end-expiratory pressure (PEEP) (a parts per thousand yen5 and a parts per thousand yen10 cmH(2)O) and two levels of FiO(2) (a parts per thousand yen0.5 and 1.0) at ARDS onset and 24 h later. Dependent upon PaO2 response, patients were reclassified into three groups: mild (PaO2/FiO(2) > 200), moderate (PaO2/FiO(2) 101-200), and severe (PaO2/FiO(2) a parts per thousand currency sign 100) ARDS. The primary outcome measure was ICU mortality. The standard ventilatory setting that reached the highest significance difference in mortality among these categories was tested in a separate cohort (n = 282). The only standard ventilatory setting that identified the three PaO2/FiO(2) risk categories in the derivation cohort was PEEP a parts per thousand yen 10 cmH(2)O and FiO(2) a parts per thousand yen 0.5 at 24 h after ARDS onset (p = 0.0001). Using this ventilatory setting, patients in the validation cohort were reclassified as having mild ARDS (n = 47, mortality 17 %), moderate ARDS (n = 149, mortality 40.9 %), and severe ARDS (n = 86, mortality 58.1 %) (p = 0.00001). Our method for assessing PaO2/FiO(2) greatly improved risk stratification of ARDS and could be used for enrolling appropriate ARDS patients into therapeutic clinical trials.