The Acute Respiratory Distress Syndrome

Abstract

).bilateral infi ltrates on chest radiograph, and 3) pulmonary artery occlusion pressure < 18 mm Hg when measured by pulmonary artery catheterization, or no clinical evidence of left atrial hypertension. Th e term ALI was adopted from the lung injury score to include patients with less severe forms of the same pathological entity. Th erefore, patients with a PaO 2 /FiO 2 of 200 to 300 were included within this group.Since its description, the American and European Consensus Conference defi nition has been widely used for enrollment of ARDS patients in therapeutic clinical trials (11-15). Nevertheless, the aforementioned defi nition also presented several shortcomings. First, the reliability in reading chest radiographs was questionable. Second, the defi nition did not explicitly defi ne the time interval for "acute." Th ird, the level of PEEP utilized during ventilation was not incorporated in the defi nition. Last, the use of pulmonary artery catheters has been decreasing over the last few years, precluding measurements of pulmonary artery occlusion pressures.Based on the aforementioned limitations, and after reviewing current epidemiologic evidence and results of clinical trials, in 2011 the European Society of Intensive Care Medicine proposed the Berlin ARDS defi nition (16), which considered the factors of timing, chest imaging, origin of edema, and oxygenation:• Of note, the term ALI has been eliminated. Th e categories of mild, moderate, and severe correlate with mortalities of 27%, 32%, and 45%, respectively (16). RISK FACTORSMultiple conditions may cause ARDS (Table 1). Sepsis remains the most common cause of ARDS, with 46% of the cases triggered by pulmonary entities (2). Mortality also varies according to the cause. Particularly, mortality in patients with ARDS due to severe trauma (injury severity score > 15) is 24.1%, whereas mortality in patients with severe sepsis with a pulmonary source is 40.6% (2). Notably, certain patientrelated variables have been associated with the risk of developing ARDS and with mortality. Among these risk factors, age (2, 17-19), male gender, African American race (20), and history of alcoholism are associated with a higher incidence and mortality (21-23). Active and passive smoking exposure increases the incidence of ARDS as well (24,25). Patients with a higher body-mass index have an increased incidence of ARDS, but its association with mortality is not clearly defi ned (26-28). Both diabetes mellitus and prehospital antiplatelet therapy seem to have a protective eff ect on development of ARDS (29-31).Interestingly, the Acute Lung Injury Verifi cation of Epidemiology (ALIVE) study (32) reported that ALI occurred in 16.1% of patients who were mechanically ventilated for other reasons. Hence, several groups have investigated a variety of methods to predict ARDS. Particularly, Gajic et al described the Lung Injury Prediction Score (LIPS , Table 2) using a prospective cohort study of 5584 patients (33). A LIPS score higher than 4 was associated with risk of developing ARDS ...