Diffuse alveolar damage Flashcards
DAD is a form of lung disease resulting from what?
Capillary wall endothelial injury
What is acute lung injury
Abrupt onset of hypoxemia and bilateral pulmonary oedema, in the abscence of cardiac failure (i.e non-cardiogenic)
What is acute respiratory distress syndrome
Manifestation of severe ALI (Clinical syndrome of progressive respiratory insufficiency)
The diffuse alveolar damage which disorders
Both pulmonary and systemic disorders
List the pulmonary and systemic disorders caused by Diffuse alveolar damage
Diffuse pulmonary infections
Gastric aspiration
Mechanical trauma including head injuries
Physical trauma/ injury e.g. Near-drowing, inhaled irritants e.g. Smoke
Chemical injury e.g. Barbiturate overdose
Hematologic conditions e.g. Transfussion-associated lung injury
Miscellaneous conditions e.g. Pancreatitis, uraemia
If idioathic= acute interstitial pneumonia
Explain the gross appearance of diffuse alveolar damage
The lungs are virtually airless, diffusely firm, and rubbery with a glistening appearance on cut section
Heavy firm red boggy lungs
Clinical the DAD is known as what?
Acute respiratory distress syndrome
Which one is caused by DAD
A. Hypoxemia
B. Hypoxia
C. Ketoacidosis
A. Hypoxemia
The lung diffusing capacity for Carbon monoxide is ?
Reduced
Which diseases causes the decreased in carbin monoxide
Diseases that affect the alveolar walls (DAD or emphysema) or the pulmonary capillary bed (Thromboembolism or vasculitis)
Injury of pneumocytes and pulmonary endothelium initiates a cycle of what?
Increasing inflammation and pulmonary damage that impairs alveolar gas exchange
The hypoxemia is exacerbated by?
Ventilation-perfusion mismatch, as the lesions are not evenly distributed.
What is Endothelial activation in DAD.
Early event
Can occur primarly as a response to circulating inflammatory mediators in severe tissue injury or sepsis, or secondary to pneumocyte injury that is sensed by resident alveolar macrophages which then secrete mediators.
List examples of mediators that are secreted in Endothelial activation
TNF that act on the endothelium
Explain the adhesion of neutrophils to activated endothelium and extravasation into interstitium and alveoli?
Neutrophils then degranulate and release inflammatory mediators and neutrophil extracellular traps, setting up the viscous cycle of inflammation and lung damage
Explain what happens when there is accumulation of intra-alveolar fluid and formation of hyaline membrane?
Occurs as the endithelial activation and injury causes leaky ulmonary capillaries. Surfactant abnormalities also occurs due to damaged Tye II alveolar pneumocytes. Hyaline membrane then form as a result of organization of the protein-rich oedema fluid and dead alveolar eithelial cells
Explain resolution of injury
If the inflmmatory stimulus is removed, macrophages remove intra-alveolar debris and secrete fibrogenic cytokines. e.g. TGF-Band PDGF, stimuating fibroblast growth and collagen deposition, resulting in fibrosis of alveolar walls. Residual type II pneumocytes proliferate to replace type I pneumocytes, and injured capillary endothelium proliferates to restore the endothelium
Explain the microspic appearance of DAD
Congestion, interstitial and intra-alveolar oedema, inflammation, fibrin deposition and hyaline membrane lining alveolar walls (fibrin-rich).
Oedema fluid is mixed with what in DAD?
Degenerating necrotic epithelial cells
What is happen in Proliferating or organizing stage of DAD?
Type II pneumocyte hyperplasia and granulation tissue. This can eventually resolve.
What is happen in Late fibrotic stage?
If granulation tissue doesn’t resolve fibrosis of alveolar septa occurs and lung compliance decreases further.
The DAD results to what?
Ventilation/Perfusion mismatches
High oxygen tension is needed of what?
Treat hypoxia resulting from DAD, and oxygen toxicity from this therapy exacerbates DAD.
Explains the clinical findings of DAD
Severe dyspnoea and tachypnoea, follwed by respiratory failure, hypoxemia and cyanosis. Loss pf functional surfactant results in lunggs becoming stoff, requiring intubation and high ventilatory pressure.
Explain radiology of DAD
Diffuse bilateral infiltrates
Explain clinical course of DAD
Moderately high mortality rate due to sepsis, multiorgan failure or severe lung injury. Most survivors recover pulmonary function but a minority develop chronic lung disease due to fibrosis
