Early Identification of Acute Respiratory Distress Syndrome in the Absence of Positive Pressure Ventilation: Implications for Revision of the Berlin Criteria for Acute Respiratory Distress Syndrome

Objectives: To assess whether patients breathing spontaneously under standard oxygen could be recognized early as acute respiratory distress syndrome patients according to the current Berlin definition. Design: A post hoc analysis from two prospective studies. Setting: Twenty-three French ICUs. Patients: All patients admitted for acute hypoxemic respiratory failure and treated with noninvasive ventilation were analyzed. Patients with cardiogenic pulmonary edema, acute exacerbation of chronic obstructive pulmonary disease, or hypercapnia were excluded. Interventions: None. Measurements and Main Results: The Pao(2)/Fio(2) ratio was estimated at admission under standard oxygen and then under non-invasive ventilation 1 hour after initiation and within the first 24 hours. Among the 219 patients treated with noninvasive ventilation for acute hypoxemic respiratory failure, 180 (82%) had bilateral infiltrates including 161 patients with Pao(2)/Fio(2) less than or equal to 300 mm Hg under standard oxygen. Among them, 127 were treated with positive end-expiratory pressure of at least 5 cm H2O, and 120 (94%) fulfilled criteria for acute respiratory distress syndrome within the first 24 hours. The mortality rate of patients with bilateral infiltrates and Pao2/Fio2 less than or equal to 300 mm Hg under standard oxygen was 29%, a rate very close to that of intubated patients with acute respiratory distress syndrome in the Berlin definition. Conclusions: Almost all patients with pulmonary bilateral infiltrates and a Pao(2)/Fio(2) less than or equal to 300 mm Hg under standard oxygen fulfilled the acute respiratory distress syndrome criteria under noninvasive ventilation within the first 24 hours. Their mortality rate was similar to that reported in the Berlin definition of acute respiratory distress syndrome. Therefore, spontaneous breathing patients with the acute respiratory distress syndrome criteria could be identified early without positive pressure ventilation.