Understanding ARDS: A Plain-Language Primer for Clinicians

Acute Respiratory Distress Syndrome (ARDS) is a sudden, severe form of lung injury in which the air sacs fill with fluid, oxygen struggles to reach the blood, and the lungs become stiff. It is not a single disease but a final common pathway triggered by many insults. This primer explains what ARDS is, how it is defined, and the cornerstones of its management.

How ARDS Is Defined

The widely used Berlin definition requires four features: onset within one week of a known insult; bilateral opacities on chest imaging; respiratory failure not fully explained by heart failure or fluid overload; and impaired oxygenation measured by the P/F ratio (PaO2 divided by FiO2) with at least 5 cm H2O of PEEP. Severity is graded as mild (P/F 200 to 300), moderate (100 to 200), or severe (under 100).

What Causes It

Common triggers include pneumonia, sepsis, aspiration of stomach contents, severe trauma, pancreatitis, and major transfusions. Pneumonia and sepsis together account for the majority of cases. The triggering insult sets off widespread lung inflammation and leaky capillaries, flooding the alveoli.

The Cornerstones of Management

• Treat the cause, for example antibiotics and source control for infection.
• Lung-protective ventilation: low tidal volumes (about 6 mL/kg of predicted body weight) and a plateau pressure under 30 cm H2O to limit further injury.
• PEEP to keep alveoli open and improve oxygenation.
• Prone positioning for moderate-to-severe ARDS, which improves oxygenation and survival.
• Conservative fluid management once shock has resolved.
• Adjuncts in severe cases: neuromuscular blockade and, in refractory hypoxemia, referral for ECMO.

Prognosis

ARDS remains serious, with mortality that rises with severity, but lung-protective strategies and prone positioning have meaningfully improved outcomes. Many survivors recover lung function, though some experience lasting physical and cognitive effects that benefit from rehabilitation.

The Bottom Line

ARDS is defined by timing, bilateral infiltrates, a non-cardiac cause, and impaired oxygenation, and it is managed by treating the trigger while protecting the lung from further harm. For in-depth, evidence-based coverage of ARDS and mechanical ventilation, explore more from the Interprofessional Critical Care Network.