A universal definition of ARDS: the PaO2/FiO2 ratio under a standard ventilatory setting—a prospective, multicenter validation study
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The PaO2/FiO2 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/FiO2 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/FiO2 ≤ 200. In the derivation cohort (n = 170), we measured PaO2/FiO2 with two levels of positive end-expiratory pressure (PEEP) (≥5 and ≥10 cmH2O) and two levels of FiO2 (≥0.5 and 1.0) at ARDS onset and 24 h later. Dependent upon PaO2 response, patients were reclassified into three groups: mild (PaO2/FiO2 > 200), moderate (PaO2/FiO2 101–200), and severe (PaO2/FiO2 ≤ 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/FiO2 risk categories in the derivation cohort was PEEP ≥ 10 cmH2O and FiO2 ≥ 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/FiO2 greatly improved risk stratification of ARDS and could be used for enrolling appropriate ARDS patients into therapeutic clinical trials.
KeywordsAcute respiratory distress syndrome Protective mechanical ventilation Standard ventilatory settings Lung injury severity Phenotype classification Definition Prognosis
This work was supported by the Instituto de Salud Carlos III (PI 07/0113, PI 10/0393) and by the Asociación Científica Pulmón y Ventilación Mecánica. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Conflicts of interest
We have the following competing interests: RMK has received research grants from Hamilton, honorarium for lecturing from Maquet and Hamilton, and is a consultant for Newport, KCL, and Bayer. JV has received research grants from Maquet. The rest of the authors declared that no competing interests exist in relation to the content of this study and manuscript.
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