Pneumothorax

Pneumothorax (PTX) refers to the presence of air in the pleural space, between the lung and the chest wall. It may happen spontaneously or secondary to emphysema, lung abscess or a fractured rib.

The pressure in the pleural cavity is normally negative to allow the lungs to expand in it. When it suddenly becomes filled with air the pressure in the pleural cavity will become equal with atmospheric pressure, causing the lung to collapse.

Tension pneumothorax is a potentially life-threatening form of pneumothorax and a medical emergency. In tension PTX air enters the pleural cavity during inspiration but cannot leave during expiration, due to the formation of a one-way valve.

Secondary pneumothorax occurs when there is a rupture of the lung close to the pleural surface that allows inhaled air to enter the pleural cavity.

Etiology

Pneumothorax may be primary or secondary. In primary pneumothorax, there is no known underlying lung condition, while in secondary pneumothorax, there is. Primary pneumothorax occurs due to the rupture of air-filled so-called subpleural bullae. These bullae are asymptomatic in most cases, but because they are thin walled, they’re predisposed to rupture. Bullae form due to overload of elastic fibres, which occurs in tall and thin people, and in weed smokers.

Primary pneumothorax risk factors:

• Family history
• Male
• Slim, tall stature
• Smoking
• Marfan syndrome

Secondary pneumothorax risk factors:

• Emphysema/COPD
• Cystic fibrosis
• TB
• Blunt trauma
• Penetrating injury
• Medical interventions
  • Mechanical ventilation
  • Thoracocentesis
  • Central venous catheter placement

Classification

We can classify pneumothorax according to several parametres:

• Whether it is caused by trauma or not
  • Spontaneous pneumothorax – PTX occurs without trauma of the chest wall
  • Traumatic pneumothorax - secondary to trauma of the chest wall
• Whether the chest wall has an open defect or not
  • Closed pneumothorax – air enters through a defect in the lung after trauma
  • Open pneumothorax – air enters through a defect in the chest wall after trauma

Pathomechanism

In any pneumothorax, air enters the pleural space from outside the chest (if caused by trauma to the chest wall) or through the lung itself (if caused by rupture of a bulla in the lung).

Spontaneous pneumothorax occurs when blebs or bullae, thin structures connected to the bronchial tree, rupture spontaneously, leaking air into the pleural cavity.

In tension pneumothorax air enters the pleural cavity during inspiration but cannot leave during expiration, due to the formation of a one-way valve. This causes the pressure inside the pleural cavity increases with each inspiration, and this increasing pleural pressure compresses venous structures, reducing venous return to the heart and shifting the mediastinum to the contralateral side. Any type of pneumothorax can progress into tension pneumothorax if the pleura or chest wall forms a one-way valve.

Clinical features

Patients with pneumothorax present with sudden, severe stabbing chest pain and, if the PTX is large enough, dyspnoea. Physical examination may reveal decreased breathing sounds and hyperresonant percussion on the affected side.

In tension pneumothorax, the increased intrathoracic pressure compresses thoracic structures like the contralateral lung, trachea, heart, and superior vena cava, causing severe symptoms, like haemodynamic instability, cyanosis, and frank obstructive shock.

Diagnosis and evaluation

The diagnosis of pneumothorax is based on a simple chest x-ray, which will show a pleural line at the border of the collapsed lung, as well as absent lung markings distal to the pleural line. The size of the pleural space (from the chest wall to the border of the collapsed lung) on the x-ray shows the "size" of the PTX. X-ray and CT may also show bullae.

Suspected tension pneumothorax is a clinical diagnosis does not undergo imaging. They proceed immediately to treatment. Should a chest x-ray be made, a mediastinal shift and tracheal deviation toward the contralateral side will be present.

Treatment

Patients with stable, mildly symptomatic, small, spontaneous pneumothorax may be treated conservatively, as they usually heal spontaneously. In case of significant symptoms, haemodynamic instability, large PTX, or trauma, a chest tube should be placed.

This tube is placed in the 4th or 5th intercostal space in the frontal axillary line (between the anterior and midaxillary lines). The tube is then connected to a water seal or a suction device. The water seal prevents air from leaking into the tube and allows for visualisation of air leaving the tube as bubbles in the water. A suction device produces negative pressure, literally sucking air out of the pleural cavity.

For tension pneumothorax, emergency decompression is necessary. A large-bore needle is inserted into the 2nd intercostal space at the midclavicular line, which immediately releases the pressure. A chest tube is then placed as described above.

Surgical treatment may be required in repeated spontaneous pneumothorax, or pneumothorax refractory to standard treatment. Surgery involves bullectomy to treat the underlying cause and applying pleurodesis (fusion of the parietal and visceral pleura, obliterating the space for air to enter). Pleurodesis may be performed mechanically, by literally sandpapering the pleura, or chemically, by applying talc or bleomycin. In case of both mechanical and chemical pleurodesis, the pleural membrane becomes inflamed, leading to fibrosis of both visceral and parietal pleura, causing them to adhere to each other, closing the pleural space.