Restrictive lung disease - ARDS and DAD Flashcards
What is ARDS?
Acute respiratory distress syndrome
A medical condition occurring in critically ill patients characterized by widespread inflammation in the lungs. ARDS is not a particular disease; rather, it is a clinical phenotype which may be triggered by various pathologies such as trauma, pneumonia and sepsis.
How is ARDS defined?
- Respiratory distress
- Reduced pulmonary compliance
- CXR - new bilateral, diffuse, patchy or homogeneous pulmonary infiltrates
- Gas exchange abnormalities
What are pulmonary causes of ARDS?
- Pneumonia
- Gastric aspiration
- Inhalation
- Injury
- Vasculitis
- Contusion
What are non-pulmonary causes of ARDS?
- Shock
- Septicaemia
- Haemorrhage
- Multiple transfusions
- DIC
- Pancreatitis
- Acute liver failure
- Trauma
- Head injury
- Malaria
- Fat embolism
- Drugs
- Eclampsia
What is the pathophysiology of ARDS?
Diffuse alveolar damage - occurs in 3 distinct phases
- Exudation
- Hyaline membrane formation
- Fibro-proliferation
What happens in the exudative phase of the pathophysiology of ARDS?
Protein rich oedema occurs within the first day following injury. This is rich in fibrin, and is similar to pulmonary oedema.
What happens in the hyaline membrane formation stage of the pathophysiology of ARDS?
Hyaline membranes are laid down as a result of exudation. These are composed of necrotic epithelial debris and exuded protein.
They line the alveolar ducts and alveolar membranes as a layer of protein. This stage is accompanied by pulmonary oedema and RBC extravasation. This occurs within 4 or 5 days.
What happens in the fibro-proliferative phase of the pathophysiology of ARDS?
This results in the formation of interstitial fibrosis and inflammation. This is the body’s attempt to organise itself, but failing.
This process occurs all over the lungs - it is not specifically confined. Gas exchange becomes inhibited due to the presence of hyaline membrane, fluid accumulation and fibrosis.
What are clinical features of ARDS?
- Central Cyanosis/hypoxameia
- Tachypnoea
- Tachycardia
- Bilateral fine inspiratory crackles
What investigations would you do in someone with suspected ARDS?
- Bloods - FBC, U+E’s, LFTs, amylase, clotting, CRP, BCs, ABG
- CXR
- Pulmonary artery catheter
What are the diagnostic criteria for the diagnosis of ARDS?
- Acute onset
- CXR - bilateral infiltrates
- PCWP < 19mmHg or a lack of CCF
- Refractory hypoxaemia
