Chapter 142: Acute Respiratory Distress Syndrome

INTRODUCTION

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.

DEFINITION

ACUTE LUNG INJURY (ALI)

American-European Consensus Conference (AECC) defined ALI by the following three criteria:

1. PaO₂:FiO₂ ≤ 300.

2. Bilateral infiltrates on chest x-ray (see Figure 142-1).

3. 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.

ARDS

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).