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Acute respiratory distress syndrome

  • Acute respiratory distress syndrome was first recognised in 1960s
  • Initially termed adult respiratory distress syndrome
  • Can occurs in both children and adults
  • Occurs following many different inflammatory insults to the lungs

Definition

  • Two condition recognised
    • Acute lung injury (ALI)
    • Acute respiratory distress syndrome (ARDS)
  • Both consist of an acute lung injury with:
    • Bilateral pulmonary infiltrates on chest x-ray
    • PCWP less than 18 mmHg
    • No evidence of left atrial hypertension
  • In ALI - PaO2 / FiO2 < 200
  • In ARDS - PaO2 / FiO2 < 300

Aetiology

  • Direct lung injury
    • Pneumonia
    • Aspiration pneumonitis
    • Pulmonary contusion
    • Fat embolism
    • Inhalational injury
  • Indirect lung injury
    • Sepsis
    • Trauma
    • Cardiopulmonary bypass
    • Acute pancreatitis

Pathology

  • Irrespective of aetiology the main pathological feature is diffuse alveolar damage
  • Endothelial injury results in increased permeability
  • Protein-rich exudate found in alveoli
  • Neutrophils are important in inflammatory process
  • Cytokines and enzymes may be responsible for many of the features
  • Resolution of inflammation can occur
  • Usually associated with some degree of pulmonary fibrosis

Clinical features

  • ARDS is usually a progressive clinical problem
  • Presents with acute respiratory failure
  • Hypoxaemia is often refractory to increasing respiratory support
  • Bilateral infiltrates present on chest x-ray
  • With time can progress to fibrosing alveolitis
  • Lung compliance is reduced and hypoxaemia persists
  • Pulmonary hypertension can progress to right heart failure
  • Resolution can occur over 6-12 months
  • Lung function can return to normal
  • Overall mortality is approximately 50%

Adult respiratory distress syndrome

Picture provided by Luke Evans, Norfolk and Norwich Hospital, Norwich, United Kingdom

Management

  • Supportive intensive care therapy is important
  • Sepsis should be treated with appropriate antibiotics
  • Careful fluid balance is important
  • Over hydration should be avoided
  • Nutritional status should be addressed
  • Mechanical ventilation is important but the exact strategy is controversial
  • Generally believed that ventilation with low tidal volumes is beneficial
  • High tidal volumes can exacerbate lung injury
  • Role of positive end-expiratory pressure unclear
  • Inhaled nitric oxide or surfactant are of no proven benefit
  • Steroids may have some beneficial effect

Bibliography

Fan E,  Needham D M,  Stewart T E.  Ventilatory management of acute lung injury and acute respiratory distress syndrome.  JAMA 2005;  28:  3124-3130.

Matthay M A.  The acute respiratory distress syndrome. N Eng J Med 2000; 342: 1334-1349.

Quinlan G J,  Evans T W.  Acute respiratory distress syndrome in adults.  Hosp Med 2000;  61:  561-563

Stott S. Recent advances in intensive care. Br Med J 2000; 320: 358-361.

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