Objectives: The American-European consensus conference (AECC) definition for acute respiratory distress syndrome (ARDS) requires a PaO(2)/F(I)O(2)< or =200 mmHg, regardless of ventilator settings. We report the results of using standardized ventilator settings to screen and enroll ARDS patients in a clinical trial of high-frequency oscillatory ventilation (HFOV), including the impact on study enrollment, and potential effects on study outcome.

Design: Prospective cohort study.

Setting: Intensive care units in two teaching hospitals. PARTICIPANTS. A consecutive sample of 41 patients with early ARDS by AECC criteria (baseline PaO(2)/F(I)O(2)< or =200) who met all other inclusion/exclusion criteria for the HFOV trial.

Interventions: Patients were placed on standardized ventilator settings (tidal volume 7-8 ml/kg, PEEP 10 cmH(2)O, F(I)O(2) 1.0), and the PaO(2)/F(I)O(2) was reassessed after 30 min.

Results: Seventeen patients (41.5%) had PaO(2)/F(I)O(2) ratios that remained < or =200 mmHg [Persistent ARDS; PaO(2)/F(I)O(2)=94+/-36 (mean+/-SD)] and went on to inclusion in the HFOV study; however, in 24 patients (58.5%) the PaO(2)/F(I)O(2) was >200 mmHg [Transient ARDS; PaO(2)/F(I)O(2)=310+/-74] and these patients were ineligible for the HFOV study. The ICU mortality was significantly greater (52.9 vs 12.5%; p=0.01) in the Persistent ARDS patients.

Conclusions: The use of these standardized ventilatory significantly impacted the PaO(2)/F(I)O(2) ratio and therefore the ARDS prevalence and trial enrollment. These results have effects on the evaluation of the current ARDS literature and conduct of clinical trials in ARDS and hence consideration should be given to the use of standardized ventilatory settings in future ARDS trials.