What defines ARDS (Acute Respiratory Distress Syndrome)?

From the Guidelines

ARDS is defined as the presence of acute arterial hypoxemia (PaO2/FiO2 ≤ 300 mmHg) with a minimum requirement of 5 cmH2O positive end-expiratory pressure (PEEP), plus the presence of bilateral radiographic opacities not entirely explained by cardiac failure or fluid overload, within 1 week of a known clinical insult.

Key Characteristics of ARDS

• Onset time: Respiratory symptoms developed/aggravated within 1 week after clinically known damage 1
• Hypoxemia: PaO2/FiO2 ratio of ≤ 300 mmHg, with PEEP or CPAP ≥ 5 cmH2O 1
• Causes of pulmonary edema: Respiratory failure cannot be completely explained by heart failure or fluid overload, with objective assessment needed to eliminate hydrostatic pulmonary edema 1
• Abnormality in imaging: Bilateral radiographic opacities not entirely explained by pleural effusion, atelectasis, or nodules 1

Classification of ARDS

• Mild: 200 < PaO2/FiO2 ≤ 300 mmHg 1
• Moderate: 100 < PaO2/FiO2 ≤ 200 mmHg 1
• Severe: PaO2/FiO2 ≤ 100 mmHg 1 The Berlin Definition, as referenced in 1 and 1, provides a standardized framework for diagnosing and classifying ARDS, which is essential for guiding clinical management and improving patient outcomes.

From the Research

Definition of ARDS

• Acute respiratory distress syndrome (ARDS) is an acute inflammatory process resulting in diffuse lung injury precipitated by an underlying risk factor 2
• ARDS is defined as noncardiogenic pulmonary edema that manifests as rapidly progressive dyspnea, tachypnea, and hypoxemia 3
• The syndrome is characterized by the onset of hypoxemia, tachypnea, and loss of lung compliance due to some stimulus 4
• ARDS is a syndrome of acute respiratory failure caused by noncardiogenic pulmonary edema 5

Diagnostic Criteria

• Diagnostic criteria include onset within one week of a known insult or new or worsening respiratory symptoms, profound hypoxemia, bilateral pulmonary opacities on radiography, and inability to explain respiratory failure by cardiac failure or fluid overload 3
• The Berlin definition classifies ARDS on a severity scale based on PaO2 (partial pressure of oxygen, arterial)/FIO2 (fraction of inspired oxygen) ratio 6

Pathogenesis

• The main pathologic mechanism of ARDS seems to result from increased alveolar permeability 6
• ARDS is thought to occur when a pulmonary or extrapulmonary insult causes the release of inflammatory mediators, promoting inflammatory cell accumulation in the alveoli and microcirculation of the lung 3
• The pathogenesis of ARDS involves lung inflammation and increased alveolar endothelial and epithelial permeabilities, leading to pulmonary edema fluid accumulation 5