Key Clinical Questions
What are the predisposing diseases/conditions that lead to acute respiratory distress syndrome (ARDS)?
How do you differentiate ARDS from other causes of hypoxemic respiratory failure?
How do you manage mechanical ventilation in ARDS?
What adjunctive therapies may benefit patients diagnosed with ARDS?
The acute respiratory distress syndrome (ARDS) describes a common disorder encountered in the critical care unit that remains a significant cause of morbidity and mortality. In the last decade standardization of ventilator strategies and overall improvement in critical care management has resulted in significant improvements in outcomes. Early vigilance in patient triage to a higher level of care (eg, transferring to the ICU), efficient identification of predisposing syndromes, and initiation of appropriate ICU interventions may prevent progression to ARDS and can minimize morbidity and mortality.
American-European Consensus Conference (AECC) defined ALI by the following three criteria:
PaO2:FiO2 ≤ 300.
Bilateral infiltrates on chest x-ray (see Figure 142-1).
Absence of left atrial hypertension or a pulmonary artery occlusion pressure ≤18 mm Hg. The third criterion excluded pulmonary edema of hydrostatic or cardiogenic origin.
Chest radiographs depicting ARDS with a patchy airspace pattern (A). ARDS can progress to a more confluent airspace pattern over time (B).
ARDS was defined by the same criteria but with worse oxygenation (PaO2:FiO2 ≤ 200), representing the subset of ALI patients with more severe hypoxemia. The AECC established a basis for years of publications on ARDS epidemiology, management, and outcomes research that could be easily applied to all patients by establishing a standard set of parameters to define ARDS.
BERLIN DEFINITION OF ARDS
The European Society of Intensive Care Medicine updated the diagnostic criteria to reflect more recent research and to address the limitations of the AECC criteria. Published in 2012, the Berlin definition eliminated the term acute lung injury that was frequently misused and created three separate and exclusive categories to reflect severity (Table 142-1).
TABLE 142-1The Berlin Definition of the Acute Respiratory Distress Syndrome |Favorite Table|Download (.pdf) TABLE 142-1 The Berlin Definition of the Acute Respiratory Distress Syndrome
|Timing ||Within 7 d of precipitating cause or onset of new/worsening respiratory symptoms |
|Chest imaging ||Bilateral airspace opacities that cannot be explained otherwise (eg, by effusions, nodules, or atelectasis) |
|Origin of chest imaging abnormality ||Not fully explained by cardiac failure or volume overload; Hydrostatic edema must be excluded if predisposing cause not present (eg, echocardiogram) |
|Oxygenation || |
| Mild ||200 < PaO2/FiO2≤ 300 with PEEP ...|