Lung and pleura

Question 1

Causes of Pulmonary Oedema

Answer 1

Leakage of excessive interstitial fluid which accumulates in the alveolar spaces
o Fluid in alveoli ↓ ability for alveoli to expand (↓ ventilation)
o Interferes with diffusion of gases across alveolar membrane
o Pre-disposes to infection

Histology
o Engorged capillaries
o Filling of airspaces with granular pink precipitate
o Accumulation of fluid in dependent areas of the lung

Causes (see table)
- Haemodynamic Distrubances
- Changes to Capillary permeability (Microvascular Injury)
- Undetermined Cause: Neurogenic, high Altitude

Question 2

Atelectasis

Answer 2

Types
- Resorption:
Due to complete obstruction of an airway. Alveoli distal to obstruction collapses
E.g. mucous plugs, foreign body aspiration, bronchial tumour
NEGATIVE mass effect on mediastinum

• Compression:
  Accumulation of fluid or air in pleural externally compresses lung
  POSITIVE mass effect on mediastinum
• Cntraction
  Restrictive lung disease prevents full expansion of lung

Question 3

ARDS

Answer 3

Acute lung injury (ALI) (also called noncardiogenic pul-
monary edema) is characterized by the abrupt onset of
significant hypoxemia and bilateral pulmonary infiltrates
in the absence of cardiac failure. Acute respiratory dis-
tress syndrome (ARDS) is a manifestation of severe ALI

Pathogenesis
- Initiated by injury of pneumocytes and pulmonary endotheliun
- Endothelial Activation
Inflammatory mediators (either locally released by damamged pneumocytes or systemically released). TNF release by alveolar macrophages
- ↑ Alveolar capillary permeability, expression of adhesion molecules, procoagulants and chemokines.
- Adhesion and Extravasation of Neutrophils recruits more inflammatory cells and causes further inflammation
- Accumulation of protein rich fluid in alveoli, Organise into Hyaline membranes
- Resolution of Injury is impeded
Ongoing inflammation impairs reabsorption of fluid. Fibrosis of alveoli walls

Pat