Acute Respiratory Distress Syndrome Flashcards
Definition
Syndrome of acute and persistent lung inflammation with increased vascular permeability
Features
- Acute onset
- Bilateral infiltrates consistent with pulmonary oedema
- Hypoxaemia
- Non-cardiogenic pulmonary oedema
- No evidence of increased left arterial pressure
- ARDS is severe – end of spectrum of acute lung injury
Aetiology
Lung damage (by either direct injury or secondary to systemic illness)
Release of inflammatory mediators
Increased capillary permeability
Fluid leakage into alveoli (pulmonary oedema)
Impaired gas exchanged and reduced lung compliance
Specific causes
- Sepsis
- Aspiration
- Pneumonia
- Pancreatitis
- Trauma/burns
- Transfusion
- Transplantation (lung or bone marrow)
- Drug overdose/reaction
Stages
- Exudative
- Proliferative
- Fibrotic
Epidemiology
Annual UK incidence = 1/6000
Presenting symptoms
Rapid deterioration of respiratory function
Dyspnoea
Respiratory distress
Cough
Any other symptoms related to the cause of ARDS
Signs on physical examination
Cyanosis
Tachypnoea
Tachycardia
Widespread inspiratory crepitations (crackles)
Hypoxia refractory (resistant) to oxygen treatment
Signs usually bilateral/may be asymmetrical in early stages of ARDS
Investigations
CXR:
• Look for bilateral alveolar infiltrates and interstitial shadowing
Bloods:
• FBC, U&Es, LFTs, ESR/CRP, amylase, ABG, blood culture
• Used to try and figure out the cause of ARDS
• Plasma BNP < 100 pg/mL could distinguish ARDS from heart failure - BNP increases in heart failure
Echocardiography:
• Check for severe aortic or mitral valve dysfunction
• Low left ventricular ejection fractions = haemodynamic anaemia not ARDS
Pulmonary artery catheterisation:
• Check pulmonary capillary wedge pressure
• Normal PCWP suggests ARDS as shows non-cardiogenic cause
Bronchoscopy:
• Used if cause cannot be determined from the history
