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Atelectasis (Collapse)

  • Incomplete expansion of the lung at birth (congenital) or collapse of previously air-filled lung (acquired)
  • Obstructive atelectasis
    • Caused by complete airway obstruction, usually by inflammatory exudate, foreign bodies, parasites, or tumours
    • In species with good collateral ventilation (dogs and cats) complete blockage of lobar or segmental bronchi is necessary for obstructive atelectasis
    • In species with poor collateral ventilation (ruminants) blockage of small bronchi and even bronchioles can result in atelectasis
    • Lobular pattern
    • Slight fluid and some macrophages may be found in the alveoli
  • Compression atelectasis
    • Caused by pleural, intrathoracic, or intrapulmonary space-occupying lesions
    • Fluid (hydrothorax), blood (haemothorax), or exudate (pyothorax) can cause compression atelectasis
    • In large animals this commonly occurs below a sharply- demarcated fluid line
  • Massive atelectasis
    • Complete lung collapse which occurs in pneumothorax due to loss of negative pressure
    • Seen in animals breathing pure or almost pure oxygen before death
    • Oxygen is absorbed very quickly into tissues and the lungs are left without any gas post mortem
  • Recumbencey (hypostatic)
    • Major risk in prolonged anaesthesia or in very weak animals
    • Shallow breathing causes poor ventilation of the dependent lung, pooled secretions and gradual loss of surfactant
  • Defective surfactant production
  • Gross: lungs are dark blue, collapsed
  • Micro: collapsed, slit-like, prominent interstitial tissue