Aetiology

The aetiology can be considered as follows: Pre-operative factors:

• pre-existing acute or chronic chest infection increase bronchial secretion and involve pathogenic bacteria
• heavy smokers are at particular risk
• emphysema, ankylosing spondylitis and other conditions which make coughing difficult in the post-operative period predispose to mucus retention.

Operative factors:

• irritant anaesthetic drugs, which increase secretion and depress the action of the bronchial cilia
• Atropine in addition increases mucus viscidity

Post-operative factors:

• thoracic or abdominal incision pain inhibits the expectoration of the accumulated bronchial secretions and is the most important cause of mucus secretion.