ARDS (2) Flashcards
Characteristics of ARDS on histological examination?
- Diffused alveolar damage
- Oedema
- Cell necrosis
- Fibrosis
What was the initial definition of ARDS?
- Acute onset hypoxia
- PaO2 to FiO2 ration < 200mmHg
- Bilateral infiltrates on CXR
- PAWP < 18mmHg or cardiogen pul oedema
What is the current Berlin definition of ARDS?
- Acute onset ARDS within 7 days of insult
- Degree of hypoxia based on PaO2/FiO2
- PEEP of at least 5
- Absence of fluid overload or CCF
- Infiltrates on CXR & CT
Classification of ARDS based on degree of hypoxaemia (PaO2/FiO2 ratio)?
- Mild - 201 and 300
- Moderate - 101 and 200
- Severe - <100 mmHg
Characteristics of ARDS?
- Precipitated by underlying factors
Distinguishing between types of ARDS?
- Pulmonary
- Extra-pulmonary
What is pulmonary ARDS?
Direct insult to the lung affecting pulmonary epithelium
What is extra-pulmonary ARDS?
Indirect lung injury caused by inflammatory mediators acting on vascular endothelium
What are the causes of pulmonary ARDS?
- Pneumonia (Main cause)
- Aspiration pneumonitis
- Inhalation injury
- Pulmonary contusion
- Pulmonary vasculitis
- Near drowning
What are the causes of extra-pulmonary ARDS?
- Non-pulmonary sepsis
- Non-cardiogenic shock
- Pancreatitis
- Major trauma
- TRALI
- Burns
- Drug overdose
What are the mimics of ARDS?
- Vasculitis (Alveolar haemorrhage)
- Drug induced
- Eosinophilic pneumonia
- Interstitial pneumonia
- Lung mets (Cancer)
What are the phases of ARDS pathophysiology?
- Exudative
- Proliferative
- Fibrosis
Features of the exudative phase of ARDS?
- Capillary congestion
- Alveolar oedema
Features of the proliferative phase of ARDS?
- Proliferation of alveolar Type-2 cells
- Proliferation of fibroblasts
- This phase can lead to resolution or formation of fibrosis
What are the intrapulmonary causes of hypoxaemia in ARDS?
- Shunt
- Dead space
- Impairment of gas diffusion
What are the mechanisms contributing to hypoxaemia in ARDS?
- Epithelial damage and increased shunt
- Endothelial damage and increased dead space
- Interstitial damage and impaired diffusion
Explain the mechanism of epithelial damage and increased shunt?
- Primary cause of hypoxaemia in ARDS
- Loss of lung volume - Surfactant deficiency
- Alveolar oedema
- Lung collapse
- Intraplulmonary shunt
Explain the mechanism of Endothelial damage and increased dead space ?
- Abnormalities in pulmonary blood flow
- The lung region is usually well ventilated
- Surrogate for dead space is ventilatory ratio
Explain the mechanism of Interstitial damage and impaired gas diffusion?
- Interstitial oedema
- Hyaline membrane
- Fibrosis - Thickened alveolar-capillary memebrane
What are the components of ventilator induced lung injury ? (VILI)
- Volutrauma
- Barotrauma
- Atelectrauma
- Biotrauma