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# Acute respiratory distress syndrome (ARDS)

Acute respiratory distress syndrome (ARDS) is a sudden, widespread lung injury in which the air sacs fill with fluid, causing severe lack of oxygen.

Updated 2026-10-30

## Structures involved

Tap one to see what it is and open it in 3D.

- [Right lower lobe](https://durgical.com/en/anatomy/inferior-lobe-of-right-lung/)
- [Left lower lobe](https://durgical.com/en/anatomy/inferior-lobe-of-left-lung/)
- [Segmental lung vessels](https://durgical.com/en/anatomy/pulmonary-trunk-chest/)
- [Pulmonary arteries](https://durgical.com/en/anatomy/right-pulmonary-artery/)
- [Trachea](https://durgical.com/en/anatomy/trachea/)
- [Diaphragm](https://durgical.com/en/anatomy/diaphragm/)
- [Right ventricle](https://durgical.com/en/anatomy/right-ventricle/)

## In biochemistry

- [Phospholipids](https://durgical.com/en/biochemistry/topics/phospholipids/)
- [Phosphatidylcholine (lecithin)](https://durgical.com/en/biochemistry/molecules/phosphatidylcholine/)

## Microorganisms that cause it

- [SARS-CoV-2](https://durgical.com/en/microbiology/sars-cov-2/)

## In histology

- [The alveolus: type I and II pneumocytes, surfactant, the blood–air barrier](https://durgical.com/en/histology/the-alveolus-type-i-and-ii-pneumocytes-surfactant-the-blood-air-barrier/)

## In the clinical exam

- [Respiratory distress and respiratory failure: the signs](https://durgical.com/en/clinical-exam/respiratory-distress-and-respiratory-failure-the-signs/)

## In physiology

- [The alveolar gas equation and the A–a gradient](https://durgical.com/en/physiology/the-alveolar-gas-equation-and-the-a-a-gradient/)
- [Ventilation–perfusion matching and West zones](https://durgical.com/en/physiology/ventilation-perfusion-matching-and-west-zones/)
- [The causes of hypoxemia](https://durgical.com/en/physiology/the-causes-of-hypoxemia/)
- [Oxygenation: SpO₂, PaO₂, cyanosis and oxygen therapy](https://durgical.com/en/physiology/oxygenation-spo-pao-cyanosis-and-oxygen-therapy/)
- [Lung and chest wall compliance](https://durgical.com/en/physiology/lung-and-chest-wall-compliance/)
- [Surface tension, surfactant and Laplace's law](https://durgical.com/en/physiology/surface-tension-surfactant-and-laplace-s-law/)
- [Physiology of pulmonary edema](https://durgical.com/en/physiology/physiology-of-pulmonary-edema/)
- [Hypoxemic and hypercapnic respiratory failure](https://durgical.com/en/physiology/hypoxemic-and-hypercapnic-respiratory-failure/)

## Why it happens

- [Vascular changes in acute inflammation: vasodilation, leakage, exudate vs transudate](https://durgical.com/en/general-pathology/vascular-changes-in-acute-inflammation-vasodilation-leakage-exudate-vs-transudat/)
- [When leukocytes injure tissue: proteases, oxidants and NETs](https://durgical.com/en/general-pathology/when-leukocytes-injure-tissue-proteases-oxidants-and-nets/)
- [How septic shock develops](https://durgical.com/en/general-pathology/how-septic-shock-develops/)
- [Shock: types, stages and the organs it damages](https://durgical.com/en/general-pathology/shock-types-stages-and-the-organs-it-damages/)

## What it is

Acute, diffuse inflammatory lung injury with leaky alveolar capillaries, causing non-cardiogenic pulmonary oedema and severe hypoxaemia. It is triggered by a direct lung insult or a systemic illness.

## Who gets it

A common reason for mechanical ventilation in intensive care, and many cases go unrecognised. Sepsis and pneumonia are the leading causes; COVID-19 greatly increased cases in Latin America. In five ICUs in Lima, Peru, 31% of 1,657 mechanically ventilated adults had ARDS at some point, with a 90-day mortality of 55–56%.

## Causes

- Direct lung injury: pneumonia (including viral), aspiration, lung contusion, inhalation injury, near-drowning
- Indirect injury: sepsis (the most common cause), major trauma, acute pancreatitis, multiple transfusions, burns
- Drug overdose and some drug reactions

## Risk factors

- Sepsis
- Severe pneumonia
- Chronic alcohol use
- Shock
- Major trauma and multiple transfusions
- Older age

## Pathophysiology

Inflammation damages the alveolar epithelium and capillary endothelium, so protein-rich fluid floods the alveoli and hyaline membranes form (diffuse alveolar damage). Surfactant loss collapses alveoli, causing shunt and stiff lungs. An exudative phase is followed by a proliferative phase and, in some patients, fibrosis.

## Classification

- Berlin definition severity, by PaO2/FiO2 with PEEP of at least 5: mild (200–300), moderate (100–200), severe (100 or less)
- Direct (pulmonary) or indirect (extrapulmonary) cause
- A newer global definition also includes patients on high-flow oxygen and uses oxygen saturation

## Symptoms and signs

- Rapidly worsening breathlessness and tachypnoea
- Hypoxaemia that responds poorly to oxygen
- Diffuse crackles
- Signs of the trigger (fever, shock, trauma)

## Red flags

- Refractory hypoxaemia
- Exhaustion or rising carbon dioxide
- Shock or multiorgan failure
- Barotrauma (pneumothorax) in ventilated patients

## Diagnosis

**Clinical**
Berlin definition: onset within one week of a known insult or new respiratory symptoms; bilateral opacities not fully explained by effusion, collapse or nodules; respiratory failure not fully explained by heart failure or fluid overload.

**Tests**
Arterial blood gas for the PaO2/FiO2 ratio; tests for the cause (cultures, lipase); BNP and ECG help rule out cardiogenic oedema.

**Imaging**
[Chest](https://durgical.com/en/anatomy/region/chest/) X-ray or CT shows bilateral opacities; echocardiography helps exclude heart failure; lung ultrasound is useful at the bedside.

## Differential diagnosis

- Cardiogenic pulmonary oedema
- Bilateral pneumonia
- Diffuse alveolar haemorrhage
- Acute exacerbation of interstitial lung disease
- Acute eosinophilic pneumonia

## Goal of treatment

Treat the cause, maintain oxygenation while avoiding further ventilator injury to the lungs, and support other organs until the lungs recover.

## Treatment

**Medical**
Treatment of the trigger: antibiotics and source control in sepsis, management of pancreatitis or trauma.

**Acute**
Lung-protective ventilation: low tidal volumes calculated from predicted body weight, limited plateau pressure and adequate PEEP.

**Acute**
Prone positioning for many hours a day in moderate to severe ARDS.

**Medical**
Conservative fluid strategy once shock resolves; sedation and, in selected severe cases, neuromuscular blockers; corticosteroids in some settings.

**Procedure**
Extracorporeal membrane oxygenation (ECMO) in experienced centres for refractory hypoxaemia.

**Rehabilitation**
Early rehabilitation and follow-up of physical, cognitive and psychological effects after intensive care.

## Complications

- Ventilator-associated pneumonia
- Barotrauma and pneumothorax
- Multiorgan failure
- Pulmonary fibrosis
- Intensive care-acquired weakness
- Long-term cognitive and psychological problems

## Prognosis

Mortality is high and rises with severity, age and the cause. Many survivors regain near-normal lung function, but weakness, fatigue and psychological problems can last months to years.

## Test yourself

Think of the answer, then tap the question to see it.

## What are the main criteria of the Berlin definition of ARDS?

Onset within one week, bilateral opacities, respiratory failure not explained by heart failure or fluids, and PaO2/FiO2 of 300 or less with PEEP of at least 5.

## What is the most common cause of ARDS?

Sepsis, followed by pneumonia and aspiration.

## What is the basic principle of ventilation in ARDS?

Lung-protective ventilation: low tidal volumes based on predicted body weight, limited plateau pressure and adequate PEEP.

## Which positioning strategy improves survival in moderate to severe ARDS?

Prone positioning for prolonged periods each day.

## What is the typical histological finding in ARDS?

Diffuse alveolar damage with hyaline membranes.

[Add to my cards (5)](https://durgical.app/estudiar/?add=/en/conditions/acute-respiratory-distress-syndrome/)

## Related conditions

- [Sepsis and septic shock](https://durgical.com/en/conditions/sepsis-and-septic-shock/)
- [Community-acquired pneumonia](https://durgical.com/en/conditions/community-acquired-pneumonia/)
- [Acute pancreatitis](https://durgical.com/en/conditions/acute-pancreatitis/)
- [Flail chest](https://durgical.com/en/conditions/flail-chest/)
- [Heart failure](https://durgical.com/en/conditions/heart-failure/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Acute Respiratory Distress Syndrome](https://www.ncbi.nlm.nih.gov/books/NBK436002/) (StatPearls (NCBI Bookshelf), 2024); [Risk factors for the development of acute respiratory distress syndrome in mechanically ventilated adults in Peru: a multicenter observational study](https://europepmc.org/article/PMC/PMC6898929) (Critical care (London, England), 2019) · adapted, [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/).

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Source: https://durgical.com/en/conditions/acute-respiratory-distress-syndrome/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/acute-respiratory-distress-syndrome/