Acute Respiratory Distress Syndrome (ARDS)

What happens in ARDS

The lungs contain millions of tiny air sacs (alveoli) wrapped in capillaries, separated by a membrane thinner than a sheet of paper. In ARDS, a direct or indirect injury triggers intense inflammation. The membrane becomes leaky and protein-rich fluid floods the air sacs. Surfactant, the substance that keeps air sacs open, is damaged, so they collapse. The lungs become stiff and heavy, and blood passes through without picking up oxygen.

ARDS develops in three overlapping phases:

1. Exudative (first week): flooding, inflammation and severe low oxygen.
2. Proliferative (weeks 1 to 3): repair begins and fluid is cleared.
3. Fibrotic (in some): scarring that can cause lasting lung stiffness.

Causes

Risk is higher with heavy alcohol use, smoking, older age and chronic illness.

Symptoms

• severe shortness of breath that worsens over hours
• rapid, labored breathing
• a fast heart rate
• low oxygen levels, which may cause confusion, drowsiness and blue lips
• cough and fever when infection is the cause
• symptoms of the underlying illness, such as abdominal pain in pancreatitis

Diagnosis

Doctors use the Berlin definition, which requires:

• onset within 1 week of a known trigger or new or worsening breathing symptoms
• patchy shadows in both lungs on chest X-ray or CT
• breathing failure not fully explained by heart failure or fluid overload
• low oxygen, measured as the ratio of blood oxygen (PaO2) to inspired oxygen (FiO2). Severity is graded mild, moderate or severe by this ratio

Tests include arterial blood gas, chest imaging, blood and sputum cultures, and an echocardiogram to rule out heart failure as the cause of pulmonary edema. Lung ultrasound is increasingly used at the bedside.

Treatment

There is no medicine that reverses ARDS directly. Treatment supports the lungs while they heal and treats the cause.

Breathing support

• Oxygen by mask or high-flow nasal cannula for milder cases.
• Mechanical ventilation through a breathing tube for most patients. Lung-protective ventilation uses small breaths (about 6 ml per kg of ideal body weight) and limits pressures, because larger breaths further injure the lungs. This approach clearly lowers death rates.
• PEEP: positive pressure at the end of each breath keeps air sacs open.
• Prone positioning: lying the patient face down for 12 to 16 hours a day improves oxygen and survival in moderate to severe ARDS.
• ECMO (extracorporeal membrane oxygenation): a machine that oxygenates blood outside the body, used in specialist centers for the most severe cases.

Other treatments

• Treating the cause: antibiotics, antivirals, source control of infection.
• Conservative fluid management once blood pressure is stable, to avoid adding fluid to the lungs.
• Sedation and sometimes short-term muscle relaxants to synchronize breathing with the ventilator.
• Corticosteroids are used in COVID-19 ARDS and are considered in some other cases.
• Supportive ICU care: nutrition, blood clot prevention, ulcer prevention and early mobilization.

Complications

• respiratory failure requiring long ventilation, sometimes with a tracheostomy
• ventilator-associated pneumonia
• collapsed lung (pneumothorax) from pressure
• blood clots
• kidney injury and multi-organ failure
• ICU-acquired weakness and delirium
• pulmonary fibrosis in some survivors

Outlook and recovery

ARDS mortality has fallen with protective ventilation but remains around 30 to 40%, and is higher in older people and with sepsis or severe disease. Many survivors' lung function returns close to normal within 6 to 12 months. However, post-intensive care syndrome is common: muscle weakness, fatigue, breathlessness on exertion, memory and concentration problems, anxiety, depression and PTSD, sometimes lasting years. Pulmonary rehabilitation, physical therapy and mental health support help recovery. Family members can also experience distress and benefit from support.

Frequently asked questions

What causes ARDS?

ARDS is caused by direct lung injury, such as pneumonia, COVID-19, inhaling vomit or smoke, or by indirect injury through the blood, such as sepsis, pancreatitis, major trauma, burns or massive transfusion. Sepsis and pneumonia are the most common causes.

What are the first symptoms of ARDS?

The first symptoms are usually breathlessness and fast breathing that worsen over hours to a day or two, in someone already ill or injured. Oxygen levels fall despite extra oxygen, and confusion or blue lips may follow. It is a medical emergency.

Can you survive ARDS?

Yes. Most people with ARDS survive, though death rates are around 30 to 40% depending on the cause, age and severity. Survival has improved with lung-protective ventilation and prone positioning.

How long does it take to recover from ARDS?

Lungs often recover substantially within 6 to 12 months. Overall recovery, including strength, stamina, memory and mood, can take a year or longer. Rehabilitation programs, physical therapy and follow-up clinics help survivors regain function.

Is ARDS the same as pneumonia?

No. Pneumonia is an infection of the lung, and it is one of the most common causes of ARDS. ARDS is the severe, widespread lung injury and fluid leakage that can follow pneumonia or other triggers, affecting both lungs.