13. Pneumothorax

DEFINITION AND CLASSIFICATION

Pneumothorax is air in the pleural space causing partial or complete lung collapse.
It may be spontaneous (primary without known lung disease; secondary with underlying lung disease), traumatic or iatrogenic.
Tension pneumothorax occurs when a one-way air leak raises intrapleural pressure, impairing venous return and causing obstructive shock.
Open pneumothorax communicates with the atmosphere through a chest-wall defect.

Primary spontaneous pneumothorax is associated with apical subpleural blebs and is more common in tall, thin young adults and smokers.
Secondary pneumothorax occurs with COPD, cystic fibrosis, interstitial lung disease, infection or malignancy.
Trauma can tear lung or chest wall; procedures such as central venous access may cause iatrogenic pneumothorax.
Air entering the pleural space abolishes negative intrapleural pressure, allowing elastic recoil of the lung.
In tension physiology, rising intrathoracic pressure shifts mediastinal structures, compresses vena cava and reduces cardiac output.

Sudden unilateral pleuritic chest pain and dyspnoea are typical.
Examination may show reduced chest expansion, hyperresonance and diminished breath sounds on the affected side.
Tension pneumothorax may cause severe respiratory distress, tachycardia, hypotension, distended neck veins (not always present), cyanosis and altered consciousness; tracheal deviation is a late sign.
Secondary pneumothorax may cause disproportionate hypoxia and rapid deterioration.