The epidemiology and definition of the acute respiratory distress syndrome.

Acute lung injury and ARDS have been clinically recognized syndromes for nearly 30 years. During that time, the understanding of the risks, pathophysiology, and outcomes has changed and improved. The definition for this disease has evolved in an attempt to identify more accurately and reliably a more homogeneous patient population that could be expected to have similar responses to the disease and therapies. The most widely accepted definition is that developed by the AECC in 1994 and now commonly used in epidemiologic studies and clinical trials. Estimates of the incidence of the disease and of mortality are significantly affected by variability in definitions used. Current estimates of the incidence of ALI, however, range from 3 to 75 cases/100,000 population/year. Mortality estimates range from 30% to 40%. Although mortality has improved from more than 60% 20 years ago, ALI survivors are still faced with an increased risk of death as well as significant decrements in physical function and quality of life through the first 12 months after hospital discharge. A great deal of progress has been made in the understanding and management of ALI patients. Now, as the search for new therapeutic options continues, equal attention must be focused on studying and improving qualitative outcomes for this group of patients.