Villar J, Pérez-Méndez L, Blanco J, Añón JM, Blanch L, Belda J, Santos-Bouza A, Fernández RL, Kacmarek RM; Spanish Initiative for Epidemiology, Stratification, and Therapies for ARDS (SIESTA) Network. Intensive Care Med. 2013 Jan 31. [Epub ahead of print]
PURPOSE: The PaO(2)/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 PaO(2)/FiO(2) calculated under a standard ventilatory setting within 24 h of ARDS diagnosis allows a more clinically relevant ARDS classification.

METHODS: 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 PaO(2)/FiO(2) ≤ 200. In the derivation cohort (n = 170), we measured PaO(2)/FiO(2) with two levels of positive end-expiratory pressure (PEEP) (≥5 and ≥10 cmH(2)O) and two levels of FiO(2) (≥0.5 and 1.0) at ARDS onset and 24 h later. Dependent upon PaO(2) response, patients were reclassified into three groups: mild (PaO(2)/FiO(2) > 200), moderate (PaO(2)/FiO(2) 101-200), and severe (PaO(2)/FiO(2) ≤ 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).

RESULTS: The only standard ventilatory setting that identified the three PaO(2)/FiO(2) risk categories in the derivation cohort was PEEP ≥ 10 cmH(2)O and FiO(2) ≥ 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).

CONCLUSIONS: Our method for assessing PaO(2)/FiO(2) greatly improved risk stratification of ARDS and could be used for enrolling appropriate ARDS patients into therapeutic clinical trials.

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