What is the definition of Acute Respiratory Distress Syndrome (ARDS)?

From the Guidelines

Acute Respiratory Distress Syndrome (ARDS) is defined as the presence within 1 week of a known clinical insult, 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, as stated in the Berlin Definition 1.

Key Criteria for ARDS Diagnosis

• Acute onset within 1 week of a known clinical insult or new/worsening respiratory symptoms
• Bilateral opacities on chest imaging not fully explained by effusions, collapse, or nodules
• Respiratory failure not fully explained by cardiac failure or fluid overload
• Impaired oxygenation with a PaO2/FiO2 ratio ≤ 300 mmHg with PEEP or CPAP ≥ 5 cmH2O

ARDS Severity Classification

• Mild: PaO2/FiO2 200-300 mmHg
• Moderate: PaO2/FiO2 100-200 mmHg
• Severe: PaO2/FiO2 < 100 mmHg The definition and classification of ARDS are crucial for guiding management and predicting outcomes, as emphasized in recent guidelines and expert opinions 1. Management of ARDS focuses on treating the underlying cause, using lung-protective ventilation strategies, appropriate PEEP, prone positioning for severe cases, and supportive care while avoiding complications like ventilator-induced lung injury.

From the Research

Definition of Acute Respiratory Distress Syndrome (ARDS)

• Acute respiratory distress syndrome (ARDS) is defined as noncardiogenic pulmonary edema that manifests as rapidly progressive dyspnea, tachypnea, and hypoxemia 2.
• It is characterized by an acute inflammatory response in the lung parenchyma, leading to alveolar edema, decreased lung compliance, and ultimately, hypoxemia 3.
• ARDS is an acute respiratory failure produced by an inflammatory edema secondary to increased lung capillary permeability, causing alveolar flooding and subsequently deep hypoxemia 4.
• The definition of ARDS comprises acute onset, bilateral patchy infiltration on chest X-ray, and a reduction of the ratio of arterial partial pressure of oxygen (PaO2) to the fraction of inspired oxygen (FiO2) 5.

Diagnostic Criteria

• Diagnostic criteria for ARDS 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 2.
• The ratio of PaO2 to FiO2 is used to classify ARDS into mild, moderate, and severe categories 5.

Pathophysiology

• 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 2.
• Inflammatory cells damage the vascular endothelium and alveolar epithelium, leading to pulmonary edema, hyaline membrane formation, decreased lung compliance, and decreased gas exchange 2.