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Expanded Explanation - Acute Respiratory Distress Syndrome
  • 08 Apr 2022
  • Medical Revision

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We provide you with a detailed overview of a topic alongside related questions in the bank. Now available in our Med Student Finals, MRCP Part 1, MRCP Part 2, MRCP PACESMSRA, MRCPCH FOP/TAS, MRCPCH AKP, MRCGP (AKT) and MRCS Part A resources.

Here is an example of an Expanded Explanation for Acute Respiratory Distress Syndrome:


Key Facts

  • Severe inflammation of the lungs results in an inefficient supply of oxygen to the body that can be life threatening.
  • Acute respiratory distress syndrome (ARDS) is severe inflammation of the lungs resulting in a life-threateningly inefficient supply of oxygen to the body.
  • ARDS is usually caused by a serious underlying health condition and most people who develop the condition are already hospitalised due to this.
  • ARDS comprises the following:
    • acute onset (within one week)
    • arterial hypoxaemia
    • bilateral, fluffy pulmonary infiltrates on chest X-ray, not explained by effusion/nodules or collapse
    • non-cardiogenic pulmonary oedema (pulmonary capillary wedge pressure <18cmH20)
    • reduced lung compliance
  • Diagnosis is based on a combination of examination and imagining findings.
  • The severity of ARDS is classified by the degree of hypoxaemia occurring.
  • Management is usually based in an Intensive Care setting with ventilation and supportive measurements as well as treating the underlying cause.
  • The mortality rate is around 1/3 of all cases; this is often due to the underlying cause.
  • Those that do survive often have no lasting lung damage.


  • Most cases of ARDS will occur in patients already admitted to hospital.
  • It can develop quickly in the community, such as patients with influenza/pneumonia/aspiration.


  • Conditions directly affecting the respiratory system include:
    • cardiopulmonary bypass
    • pulmonary contusion
    • smoke inhalation
    • oxygen toxicity
    • pneumonia
    • near-drowing
    • aspiration of gastric contents
  • Other conditions include:
    • sepsis
    • burns
    • disseminated intravascular coagulation (DIC)
    • pancreatitis, uraemia
    • drug overdoses (e.g. diamorphine, methadone, barbiturates, paraquat)
    • trauma


  • Damage to capillary endothelium and alveolar epithelium and increased capillary permeability result in an accumulation of protein-rich fluid in the alveoli, causing diffuse alveolar damage.
  • Activation of neutrophils causes inflammation and further lung damage.

Clinical Presentation

  • Patients with ARDS can present with the following:
    • severe shortness of breath
    • raised respiratory rate
    • shallow breathing
    • drowsiness
    • confusion
    • feeling lightheaded

Differential Diagnosis

  • Some differential diagnosis of ARDS include:
    • panic attack
    • diabetic ketoacidosis (in early stages, the breathing in shallow and can progress to Kussmaul breathing, indicating severe metabolic acidosis)
    • asthma attack
    • carbon monoxide poisoning


  • Diagnosis and investigations for ARDS are as follows:
    • blood including septic screen, cultures
    • blood gases
    • pulse oximetry
    • chest X-ray - pulmonary oedema, bilateral alveolar shadowing, air bronchograms
  • Other investigations may include echocardiogram and urine culture. This depends on the clinical scenario and suspected underlying cause.


  • No specific treatment is available for ARDS, and management is essentially supportive.


  • Management is guided by the severity of hypoxaemia: 
    • mild (200 mm Hg < PaO2/FiO = 300 mmHg)
    • moderate (100 mm Hg < PaO2/FiO = 200 mmHg)
    • severe (PaO2/FiO = 100 mmHg)
  • Patients usually require management within the Intensive Care Unit.
  • Supplemental oxygen is given and patients frequently require mechanical ventilation:
    • pressure-controlled, inverse-ratio ventilation is used because this lowers peak airway pressure, reduces barotrauma and creates better distribution of gas in the lungs
    • with the addition of positive end-expiratory pressure (PEEP), there is greater alveolar recruitment, increased functional residual capacity, better lung compliance and reduced shunt
    • turning the patient into the prone position intermittently allows those dependent parts of the lung that are susceptible to atelectasis to re-expand and improves blood flow to the ventilated parts of the lung
  • Guidelines from the American Thoracic Society/European Society of Intensive Care Medicine/Society of Critical Care Medicine Clinical Practice:
    • for all patients with ARDS, the recommendation is strong for mechanical ventilation using lower tidal volumes and lower inspiratory pressures
    • for patients with severe ARDS, the recommendation is strong for prone positioning for more than 12 h/d
    • for patients with moderate or severe ARDS, the recommendation is strong against routine use of high-frequency oscillatory ventilation and conditional for higher positive end-expiratory pressure and recruitment manoeuvres
  • Additional evidence is necessary to make a definitive recommendation for or against the use of extracorporeal membrane oxygenation in patients with severe ARDS.
  • Other supportive measures include IV hydration and nutritional support, and venous thromboembolism prophylaxis.


  • Sepsis should be treated empirically until causative organisms are identified.
  • Inhaled nitric oxide (NO) causes selective vasodilatation of the ventilated areas of the lung when inhaled at low concentrations.
  • Corticosteroids have been shown to be beneficial in the latter stages of ARDS (ie progressive pulmonary interstitial fibroproliferation is present).


  • The prognosis of ARDS is:
    • associated with substantial morbidity
    • fatal in 1/3 of cases, though usually due to the underlying illness and not directly as a result of ARDS
  • The lungs make a full recovery in most cases of those who survive.


  • The use of exogenous surfactant in adult patients has no proven value.


Acute respiratory distress syndrome (ARDS)


NHS UK Acute respiratory distress syndrome

  • 08 Apr 2022
  • Medical Revision