Acute respiratory distress syndrome

Overview

Acute Respiratory Distress Syndrome (ARDS) is a severe, life-threatening condition in which the lungs become inflamed and filled with fluid, leading to significant breathing difficulties and reduced oxygen levels in the bloodstream. ARDS is a type of non-cardiogenic pulmonary edema and is commonly seen in critically ill patients. It typically requires intensive care and mechanical ventilation. ARDS can occur as a result of various underlying conditions and often progresses rapidly, making early recognition and treatment essential.

Causes

ARDS is not a disease itself but a clinical syndrome triggered by direct or indirect injury to the lungs. Common causes include:

Direct Lung Injury:

• Pneumonia

• Aspiration of gastric contents

• Inhalation injury (e.g., smoke, toxic gases)

• Near-drowning

Indirect Lung Injury:

• Sepsis (most common overall cause)

• Severe trauma

• Pancreatitis

• Massive blood transfusions (transfusion-related acute lung injury, TRALI)

• Drug overdose or adverse drug reactions

Symptoms

Symptoms of ARDS typically develop within hours to days after the triggering event and can escalate quickly. They include:

• Severe shortness of breath (dyspnea)

• Rapid breathing (tachypnea)

• Hypoxemia: Low oxygen levels not responding to supplemental oxygen

• Cyanosis: Bluish discoloration of the skin, lips, or nails

• Confusion, restlessness, or fatigue

• Low blood pressure (in advanced or septic cases)

In critical cases, ARDS leads to respiratory failure requiring mechanical ventilation and intensive care.

Diagnosis

Diagnosis of ARDS is based on clinical, radiographic, and laboratory criteria. The Berlin Definition is widely used and includes:

• Acute onset: Within 1 week of a known clinical insult

• Bilateral opacities: Seen on chest X-ray or CT, not fully explained by effusion, collapse, or nodules

• Respiratory failure not fully explained by cardiac failure or fluid overload

• Impaired oxygenation: Assessed by the PaO₂/FiO₂ ratio (partial pressure of oxygen to fraction of inspired oxygen)

Additional tests may include:

• Blood gases (to measure oxygen and carbon dioxide levels)

• Chest imaging (X-ray or CT)

• Blood cultures, sputum cultures, or bronchoalveolar lavage to identify infections

• Echocardiogram to exclude cardiogenic causes

Treatment

There is no specific cure for ARDS; treatment focuses on supportive care and addressing the underlying cause. Key components include:

Respiratory Support:

• Mechanical ventilation: Using lung-protective strategies (low tidal volumes and controlled pressures)

• Prone positioning: Lying face-down to improve oxygenation in severe cases

• High-flow nasal oxygen or non-invasive ventilation: In mild cases or early stages

Medical Management:

• Management of the underlying condition: Such as antibiotics for sepsis or pneumonia

• Fluid management: Conservative strategy to reduce lung edema

• Medications: Sedation, analgesia, and sometimes corticosteroids (depending on cause and timing)

Advanced Therapies (in severe or refractory ARDS):

• Extracorporeal Membrane Oxygenation (ECMO)

• Neuromuscular blockade (temporarily paralyzing muscles to improve ventilation)

Prognosis

The prognosis of ARDS varies depending on the underlying cause, severity, age, and comorbidities. Mortality rates range from 25% to over 50% in severe cases, especially in older adults or patients with multi-organ failure.

Among survivors:

• Many recover full lung function over weeks to months

• Some may experience long-term complications such as reduced exercise capacity, chronic lung disease, or PTSD

• Early rehabilitation and follow-up care are essential for recovery