Acute respiratory distress syndrome
Updates to Article Attributes
Acute respiratory distress syndrome (ARDS) occurs as a result of severe pulmonary injury that cause alveolar damage heterogeneously throughout the lung. It can either result from a direct pulmonary source or as a response to systemic injury.
Pathology
Lung damage results in leakage of fluid into alveoli, leading to non cardiogenic pulmonary oedema and decreased arterial oxygenation.
The diagnosis is based on mainly clinical criteria set forth by the American-European Consensus Conference 4. ARDS is characterised by the following criteria 7:
- lung injury of acute onset, within one week of an apparent clinical insult and with progression of respiratory symptoms
- bilateral opacities on chest imaging not explained by other pulmonary pathology (e.g. pleural effusion, pneumothorax, or nodules)
- respiratory failure not explained by heart failure or volume overload
- decreased arterial
PaO2/FiO2PaO2/FiO2 ratio- mild ARDS: ratio is 201-300 mmHg (≤39.9 kPa)
- moderate ARDS: 101-200 mmHg (≤26.6 kPa)
- severe ARDS: ≤100 mmHg (≤13.3 kPa)
It is of note that the clinical diagnosis of ARDS using internationally accepted guidelines and chest radiographs, has been demonstrated to correlate poorly with histopathological diagnosis at autopsy.8, 9
Causes
- trauma
- septicaemia
- hypovolaemic shock
- fat embolism
- near-drowning
- burns
- viral pneumonia
- pancreatitis
- oxygen toxicity
- smoke inhalation
- disseminated intravascular coagulopathy
- transfusion reaction
- aspiration of gastric contents
- head injury
Radiographic features
Chest radiograph
Chest radiographic findings of ARDS are nonspecific and resemble those of typical pulmonary oedema or pulmonary haemorrhage. There are diffuse bilateral coalescent opacities (the only radiologic criterion defined by the Consensus Conference). The time course of ARDS may help in differentiating it from typical pulmonary edemaoedema.
Chest x-ray features usually develop 12-24 hours after initial lung insult as a result of proteinaceous interstitial oedema. Within one week, alveolar pulmonary oedema (hyaline membrane) occurs due to type 1 pneumocyte damage.
In contrast to cardiogenic pulmonary oedema, which clears in response to diuretic therapy, ARDS persists for days to weeks. In addition, as the initial radiographic findings of ARDS clear, the underlying lung appears to have a reticular pattern secondary to type 2 pneumocyte proliferation and fibrosis 4.
Treatment and prognosis
ARDS carries a high mortality of around 50% 2 and many survivors develop chronic lung disease, with damaged lung healing by fibrosis. A minority recover fully.
-<li>decreased arterial PaO2/FiO2 ratio<ul>- +<li>decreased arterial PaO<sub>2</sub>/FiO<sub>2</sub> ratio<ul>
-</ul><h4>Radiographic features</h4><h5>Chest radiograph</h5><p>Chest radiographic findings of ARDS are nonspecific and resemble those of typical pulmonary oedema or pulmonary haemorrhage. There are diffuse bilateral coalescent opacities (the only radiologic criterion defined by the Consensus Conference). The time course of ARDS may help in differentiating it from typical pulmonary edema.</p><p>Chest x-ray features usually develop 12-24 hours after initial lung insult as a result of proteinaceous interstitial oedema. Within one week, alveolar pulmonary oedema (hyaline membrane) occurs due to type 1 pneumocyte damage.</p><p>In contrast to cardiogenic pulmonary oedema, which clears in response to diuretic therapy, ARDS persists for days to weeks. In addition, as the initial radiographic findings of ARDS clear, the underlying lung appears to have a reticular pattern secondary to type 2 pneumocyte proliferation and fibrosis <sup>4</sup>.</p><h4>Treatment and prognosis</h4><p>ARDS carries a high mortality of around 50% <sup>2 </sup>and many survivors develop chronic lung disease, with damaged lung healing by fibrosis. A minority recover fully.</p>- +</ul><h4>Radiographic features</h4><h5>Chest radiograph</h5><p>Chest radiographic findings of ARDS are nonspecific and resemble those of typical pulmonary oedema or pulmonary haemorrhage. There are diffuse bilateral coalescent opacities (the only radiologic criterion defined by the Consensus Conference). The time course of ARDS may help in differentiating it from typical pulmonary oedema.</p><p>Chest x-ray features usually develop 12-24 hours after initial lung insult as a result of proteinaceous interstitial oedema. Within one week, alveolar pulmonary oedema (hyaline membrane) occurs due to type 1 pneumocyte damage.</p><p>In contrast to cardiogenic pulmonary oedema, which clears in response to diuretic therapy, ARDS persists for days to weeks. In addition, as the initial radiographic findings of ARDS clear, the underlying lung appears to have a reticular pattern secondary to type 2 pneumocyte proliferation and fibrosis <sup>4</sup>.</p><h4>Treatment and prognosis</h4><p>ARDS carries a high mortality of around 50% <sup>2 </sup>and many survivors develop chronic lung disease, with damaged lung healing by fibrosis. A minority recover fully.</p>