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