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DIAGNOSIS

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The acute respiratory distress syndrome (ARDS), first identified by Ashbaugh et al. in 1967, described a constellation of findings in 12 patients who had experienced acute onset of tachypnea, hypoxemia, loss of lung compliance, cyanosis refractory to oxygen therapy, and diffuse alveolar infiltration on chest radiograph. Pathologic examination from seven of these patients found atelectasis, vascular congestion with hemorrhage, hyaline membranes, and pulmonary edema.1

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The initial description by Ashbaugh et al. provided vague criteria for diagnosis and was not specific enough to exclude other conditions. In 1988, Murray et al. developed a 4 point lung injury scoring system in an effort to better define the syndrome using specific and measurable criteria. The components of the score included alveolar consolidation measured by chest radiograph, hypoxemia measured by PaO2/FiO2 ratios, levels of required positive end-expiratory pressure (PEEP), and pulmonary compliance.2

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In 1994, the American–European Consensus Committee (AECC) on ARDS implemented new criteria for the diagnosis of ARDS. It allowed for those with less severe hypoxemia to be classified as having acute lung injury (ALI) and those with more severe hypoxemia to be defined as having ARDS. The AECC defined ALI as the acute onset of respiratory distress with PaO2/FiO2 <300 mm Hg, bilateral, patchy infiltrates on chest radiograph, and a pulmonary artery occlusion pressure (PAOP) <18 mm or absent clinical evidence of left atrial hypertension (indicating presumptive non-cardiac etiology of pulmonary edema). ARDS was given similar diagnostic criteria, but with PaO2/FiO2 <200 mm Hg.3 The AECC definition of ARDS resulted in advancement in clinical and epidemiologic data, thereby improvements in care for patients with ARDS. However, after nearly two decades of use, a number of limitations with the AECC criteria persisted. In order to address these limitations, an international panel of experts convened in 2011 and developed the Berlin Definition of ARDS.4

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The Berlin Definition of ARDS defined the term acute, eliminated the term ALI, and stratified ARDS into mild, moderate and severe based on the degree of hypoxemia by PaO2: FiO2 ratios. The definition requires a minimal PEEP of ≥5 cm H2O, clarifies the radiographic criteria, and removes the PAWP requirement and defined risk factors (Table 11-1). This new definition was retrospectively evaluated against 3670 individuals from 4 multicenter randomized control trials (RCTs), 269 patients from 3 single-center trials and against the AECC definition. Retrospective analysis showed increasing mortality associated with severity and increasing median duration of mechanical ventilation (MV) with increasing severity.4

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Table Graphic Jump Location
TABLE 11-1:

The Berlin Definition of Acute Respiratory Distress Syndrome

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