Values for 28 or 30-day mortality or hospital mortality in patients with ALI/ARDS vary considerably, ranging from about 30-60% [1,4, 8, 9]. In the Esteban international study, the mortality listed for ARDS is 52% . In a prospective cohort study from Sweden, Denmark and Iceland the 90 day mortality was 42% for ALI not fulfilling ARDS criteria and similar at 41% for ARDS . In a recent one-year study of ALI in King County, Washington, USA in which all ventilated patients were systemically screened for the diagnosis of ALI, the overall mortality was 34% . A number of variables affect the mortality rate including age and underlying etiology or risk condition of ALI, making comparisons between cohorts difficult without having detailed data on case-mix and comorbid states. Suntharalingam and colleagues reported a statistically insignificant trend of higher hospital mortality in patients with ARDS from a pulmonary (direct) etiology compared to those with ARDS from a non-pulmonary (indirect) etiology (47 vs. 28%, p=0.11) .
Our group at the University of Washington in Seattle, USA first reported on a declining hospital mortality rate for patients with ARDS in 1995 . Using data from a registry of ARDS patients available since the early 1980s in which patients were prospectively screened for a diagnosis of ARDS using the same criteria, we showed a reduction in hospital mortality from greater than 60% in the 1980s to less than 40% in the early 1990s. The hospital in which the study was performed, Harborview Medical Center, is the major trauma referral center for a five state region. Trauma as a risk condition for ALI or ARDS is known to be associated with a lower mortality than other common risk conditions, particularly sepsis, which may explain our relatively lower mortality compared to other studies. The reduction in mortality rate over time, however, was related more to a decreased mortality in patients with sepsis as their ARDS risk. The severity of illness as judged by APACHE score was similar comparing the earlier years with a high mortality to later years with a lower mortality. The reduction was not affected after adjusting for frequency of risk conditions and age. Since our report, two other groups have reported a reduction in mortality rate overtime, one report from England  and another from France .
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