Incidence of Acute Lung Injury: The Alien Study (ALIEN)

Acute lung injury (ALI) is a clinical syndrome of rapid onset of non-cardiogenic pulmonary edema manifested clinically by hypoxemia (PaO2/FiO2≤300 mmHg) and bilateral pulmonary infiltrates. When the hypoxemia is severe (PaO2/FiO2≤200 mmHg) it is termed the acute respiratory distress syndrome (ARDS). It represents a significant public health issue. Patients with ALI or ARDS require admission into critical care units for advanced life support and utilize considerable health care resources.

An immense plethora of translational knowledge has been acquired since the first description of ARDS in 1967. However, estimates of the incidence of ARDS and ALI have varied widely, and the true magnitude of this health problem still remains unclear. Current estimates of the incidence of ALI/ARDS range from 15 to 80 cases per 100.000 population, or almost 40.000 cases per year in Spain. Combined mortality rates for ALI/ARDS range between 30-45%. ALI and ARDS occur as a complication or as the primary cause of critical illness in patients, usually after severe infection or trauma.

Published epidemiological studies on ALI and ARDS in the last 20 years are difficult to compare. Some reports have used different definitions for ALI and ARDS and others have evaluated the incidence during a short period of time (from days to several weeks) and then extrapolated their data to estimates of a one-year incidence. Very few studies have collected information for an entire year, and none of them have evaluated the degree of hypoxemia under standard ventilatory settings, as it has been proposed recently by the HELP Network (Am J Respir Crit Care Med 2007; 176:795-804).

As a result, we propose to perform a one-year prospective audit of all ALI and ARDS patients managed in 40 ICUs from 17 Spanish provinces (15 provinces in the mainland and 2 provinces in the Canary Islands). We intend to collect data from all patients admitted with or developing ALI/ARDS with the aim to understand the epidemiology and natural history of acute lung injury. These provinces are scattered through the Spain and are representative of the demographic differences across the country.