Purpose: We previously reported a study of systemic inflammatory response syndrome (SIRS) cases in the Tohoku district of Japan in which the patients showed a 30-day mortality from acute lung injury/acute respiratory distress syndrome (ALI/ARDS) of about 20%. Cases in which chest X-ray findings did not meet ALI/ARDS criteria were diagnosed as acute hypoxemic respiratory failure (AHRF), but about 50% of these patients progressed to ALI/ARDS. The objective of this study was to verify the findings obtained in the earlier study and to gain further insights into the pathognomonic symptoms of AHRF associated with SIRS. Methods: A prospective cohort study was performed in SIRS patients admitted to the intensive care unit (ICU) with PaO2/fractional inspired oxygen (FIO2) ≤ 300 mmHg. Patients were assigned to ALI or ARDS groups based on symptoms at ICU entry. Cases in which chest X-ray showed no infiltration shadows in bilateral lung fields were classified as AHRF. Results: A total of 240 patients were enrolled in the study. The 30-day mortalities were 21.6% and 20.0% in the ALI and ARDS groups, respectively. Of the 88 AHRF patients, 49 progressed to ALI/ARDS, with progression occurring within 3 days after ICU entry in most cases; 39 patients recovered with no progression. Chest X-ray and computed tomography (CT) showed no findings indicating ALI/ARDS in 20 AHRF patients at ICU entry, but 7 of these patients progressed to ALI/ARDS. Conclusion: The mortality rates of ALI and ARDS were 21.6% and 20.5%, respectively. More than half of the AHRF patients progressed to ALI or ARDS. Some AHRF patients had normal findings on chest CT, but subsequently showed a bilateral shadow on a chest X-ray. This indicates that mild pathologic lesions may not show imaging abnormalities.
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