, Volume 29, Issue 11, pp 1936-1942
Date: 04 Sep 2003

Impact of positive end-expiratory pressure on the definition of acute respiratory distress syndrome

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We examined whether PEEP during the first hours of ARDS can induce such a change in oxygenation that could mask fulfillment of the AECC criteria of a PaO2/FIO2 ≤ 200 essential for ARDS diagnosis.

Design and setting

Observational, prospective cohort in two medical-surgical ICU in teaching hospitals.


48 consecutive patients who met AECC criteria of ARDS on 0 PEEP (ZEEP) at the moment of diagnosis.

Measurements and results

PaO2/FIO2 and lung mechanics were recorded on admission (0 h) to the ICU on ZEEP, and after 6, 12, and 24 h on PEEP levels selected by attending physicians. Lung Injury Score (LIS) was calculated at 0 and 24 h. PaO2/FIO2 rose significantly from 121±45 on ZEEP at 0 h, to 234±85 on PEEP of 12.8±3.7 cmH2O after 24 h. LIS did not change significantly (2.34±0.53 vs. 2.42±0.62). These variables behaved similarly in pulmonary and extrapulmonary ARDS, and in survivors and nonsurvivors. After 24 h only 18 patients (38%) still had a PaO2/FIO2 of 200 or lower. Their mortality was similar to that in the remaining patients (61% vs. 53%).


The use of PEEP improved oxygenation such that one-half of patients after 6 h, and most after 24 h did not fulfill AECC hypoxemia criteria of ARDS. However, LIS remained stable in the overall series. These results suggest that PEEP level should be taken into consideration for ARDS diagnosis.