10th January 2024

Background

Pneumothorax refers to air within the pleural cavity. There are several definitions to be aware of when considering pneumothorax:

• Primary spontaneous pneumothorax. Refers to the development of a pneumothorax in the absence of an external event without the presence of underlying lung disease.
• Secondary spontaneous pneumothorax. Refers to the development of a pneumothorax in the absence of an external event, with the presence of underlying lung disease, e.g. asthma or chronic obstructive pulmonary disease (COPD).
• Traumatic pneumothorax. Refers to the development of a pneumothorax following an external event. This can further be subdivided into iatrogenic (secondary to a medical procedure) and non-iatrogenic (secondary to blunt or penetrating chest injury).

The focus of this section is going to be on primary and secondary spontaneous pneumothorax.

Epidemiology

Primary and secondary spontaneous pneumothoraces are common pathologies that emergency physicians, respiratory physicians and intensive care physicians encounter. Combined hospital admission rates are quoted at 16.7/100,000 for men and 5.8/100,000 for women. Both primary and secondary pneumothoraces are seen at a higher incidence in the male population, with risk factors such as being tall, with low BMI, and cigarette smoking identified.

Primary spontaneous pneumothoraces are seen in a younger population demographic (typically 20-30 years old), whereas secondary spontaneous pneumothoraces are seen in an older population (typically 60-65 years old), reflecting the development of underlying lung disease.

Pathophysiology

In normal breathing, air does not enter the pleural cavity at any point. Therefore, The presence of air signifies the development of pathology from communication between the alveolar spaces and pleura, from communication between the outside atmosphere and the pleural space, or from the presence of gas-producing organisms within the pleural space.

Primary Spontaneous Pneumothorax (PSP) 

The mechanism which results in a primary spontaneous pneumothorax is not currently fully understood; however, it has been identified that the majority of patients who present with PSP do have an underlying anatomical abnormality, even in the absence of known lung disease. These “anatomical abnormalities” are typically described as subpleural blebs and bullae, more commonly found at the lung apex. Risk factors for the development of these anatomical abnormalities include cigarette smoke, poor nutritional status with low BMI, connective tissue disease (including Marfan’s syndrome) and hereditary predisposition. It is thought that these subtle anatomical differences, when combined with the appropriate precipitating factor, result in the development of the primary spontaneous pneumothorax. Lung inflammation and oxidative stress are also likely to play an important role in the development of PSP.

Smoking is one of the biggest implicating factors for spontaneous pneumothorax (with BTS quoting a healthy smoking male having a 12% lifetime risk of pneumothorax development, whereas the same demographic non-smoking male is just 0.1%).

Secondary Spontaneous Pneumothorax (SSP) 

Secondary spontaneous pneumothorax (SSP) is pneumothorax associated with underlying lung disease, and many underlying chronic lung diseases have been recognised to increase the risk of pneumothorax development. The most common association is with airways disease: chronic obstructive pulmonary disease (COPD), severe asthma and cystic fibrosis. Infections such as pneumocystis carinii can also increase the risk of SSP development.

Tension Pneumothorax 

A tension pneumothorax is a potentially life-threatening medical emergency that occurs as a result of the development of a one-way valve system in the pleural space. This one-way system allows air in during inspiration but fails to let air out in expiration, causing progressively larger volumes of air within the pleural space. This raises intrapleural pressures, impairing venous return to the heart, which eventually results in hypotension, tachycardia and, ultimately, cardiovascular collapse.