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.
KeywordsAcute lung injury Acute respiratory distress syndrome Hypoxemia Diagnosis Positive end-expiratory pressure Mechanical ventilation
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