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


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 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).


RESULTS
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).


CONCLUSIONS
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.
CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain. jesus.villar54@gmail.com
Jesús
J
Villar
Lina
L
Pérez-Méndez
Jesús
J
Blanco
José Manuel
JM
Añón
Lluís
L
Blanch
Javier
J
Belda
Antonio
A
Santos-Bouza
Rosa Lidia
RL
Fernández
Robert M
RM
Kacmarek
D000328:Adult; D001784:Blood Gas Analysis / Q000592:standards* / Q000706:statistics & numerical data; D006801:Humans; D011175:Positive-Pressure Respiration / Q000379:methods; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012128:Respiratory Distress Syndrome / Q000097:blood / Q000145:classification* / Q000175:diagnosis; D012720:Severity of Illness Index