Atelectasis

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