Family doctor

What is a pneumothorax?

A pneumothorax is defined as free air (pneumo) trapped within the chest cavity (thorax) &endash; but not within the lungs themselves. More specifically, the air is trapped within the 'intrapleural space'. The intrapleural space is normally just a 'potential space' that exists between two layers of 'pleura' &endash; thin tissue layers, one of which covers lungs, and one of which lines the chest cavity.

 Normally the air pressure within the intrapleural space is negative (which helps keep the two layers of pleura together), while that in the lungs and airways is negative with breathing in, and positive with breathing out. If a defect occurs in the pleura covering the lungs, then the air from within the lungs 'escapes' into the intrapleural space, resulting in a pneumothorax. Alternatively, a penetrating injury to the chest wall can injure the pleura lining the chest cavity, again allowing air to enter the intrapleural space. As air enters the intrapleural space, the air pressure within the pleural cavity rises, causing collapse of the lung on that side. The collapse continues until the air pressures within the intrapleural space and lungs/airways equalise, or the defect in the pleura seals. If untreated, the pneumothorax with resolve, as the air within the intrapleural space is gradually resorbed.

 If the trapped air within the intrapleural space is at much greater pressure than that in the lungs, equalisation of air pressures may not occur. This is called a 'tension pneumothorax', a critical condition resulting in severe constriction of the lung on the affected side, compression of the opposite lung, and displacement of the heart and its associated blood vessels. Tension pneumothorax is a medical emergency.

 What causes a pneumothorax to occur?

In general, pneumothorax is classified as spontaneous or traumatic. Spontaneous pneumothorax is 'primary' if it occurs without any pre-existing condition, or 'secondary' if it occurs in association with another disease (usually of the lungs). Traumatic pneumothorax arises after blunt or penetrating trauma to the chest. 'Iatrogenic' pneumothorax is that which follows a diagnostic or therapeutic medical procedure (e.g. needle aspiration of a lung sample through the chest wall, or placement of an intravenous catheter in one of the great vessels in the lower neck). This article is concerned with spontaneous pneumothorax.

 Primary spontaneous pneumothorax probably occurs when a bleb (a small air-filled cyst structure beneath the pleura) ruptures. The cause of blebs remains uncertain; they are found more frequently in patients with spontaneous pneumothorax, even those who are non-smokers.

 Secondary spontaneous pneumothorax occurs as a result of many diseases, the majority of which are lung-related. Table I gives examples of causes of secondary pneumothorax. The most common cause is airway disease, which is implicated in 30-59% of cases of secondary pneumothorax. Historically, tuberculosis was the most frequent infectious cause of secondary spontaneous pneumothorax, but that role is now taken by Pneumocystis carinii pneumonia in HIV-infected patients. Secondary pneumothorax occurs in association with the high air pressures that occur in lungs with airways disease (especially with coughing fits), or because of rupture of lung tissue in association with infection or interstitial diseases. An unusual rare cause is that associated with endometriosis. In such cases, 'catamenial pneumothorax' occurs within 72 hours of menstruation.

 Table I: Causes of secondary spontaneous pneumothorax

Who gets pneumothorax?

Primary spontaneous pneumothorax typically occurs in young men aged 20-40 years, especially those who are tall and thin. It usually occurs while the patient is at rest. Smoking increases the likelihood of primary spontaneous pneumothorax up to 20 times; changes in atmospheric pressure (e.g. aviation, scuba diving) may be a factor.

 Secondary spontaneous pneumothorax also affects men more than women, but the peak incidence is much later in life (reflecting the peak age for chronic bronchitis and emphysema).

 What are the symptoms of pneumothorax?

Primary pneumothorax is usually associated with pain and shortness of breath. The pain is on the affected side and is initially sharp and worse with deep breathing), but later becomes a steady ache. Both symptoms usually subside within 24 hours, even if the pneumothorax is untreated and has not yet resolved.

 Secondary pneumothorax in patients with associated lung disease causes severe shortness of breath; pain is also common. Unlike the primary variant, symptoms do not resolve spontaneously.

 How is pneumothorax diagnosed?

Pneumothorax (whatever the cause) is usually diagnosed from the symptoms. The exception is those with underlying lung disease, as the symptoms of pneumothorax may be difficult to distinguish from those of the associated condition. A physical examination may be normal in those with a small pneumothorax, apart from a rapid heart rate. In patients with a larger pneumothorax, a careful chest examination will elicit specific signs that physicians should be aware of.

 Patients with tension pneumothorax are severely distressed, and have signs of collapse: a thready, rapid pulse and low blood pressure.

 A chest x-ray is used to confirm the diagnosis, although special views may be required in those with a small pneumothorax. Patients with underlying lung airways disease may also need a CT scan, as the diagnosis may be more difficult to confirm from a chest x-ray. Such patients will also have specific blood tests performed, to measure the amounts of oxygen and carbon dioxide in their blood.

 How is pneumothorax treated?

The treatment of primary spontaneous pneumothorax depends largely on its size. Previously well patients with no symptoms and only a small pneumothorax may be managed by observation alone (with repeat chest x-rays). Those with a bigger pneumothorax or symptoms are generally treated by removing the trapped air from within the intrapleural space, allowing the lung to re-expand. This can be achieved by aspirating it via a catheter or by 'thoracostomy' (insertion of a chest tube that is left in place for a number of days).

 Occasionally there is persistence of the air leak responsible for the pneumothorax. In such cases, initial treatment is with a chest tube; however, lung surgery to repair the air leak is recommended if the air leak persists after 7 days in patients with primary spontaneous pneumothorax. In those with secondary spontaneous pneumothorax, surgery to repair the leak and prevent recurrences may be recommended at the outset, or only after 2 weeks of chest tube drainage.

 Does spontaneous pneumothorax recur?

Spontaneous pneumothorax is unfortunately often a recurrent condition. Recurrence occurs in 16-52% of those with primary spontaneous pneumothorax (usually within 6-24 months of the initial episode and more commonly in smokers and younger patients) and 39-47% of those with secondary spontaneous pneumothorax.

 Various procedures have been developed to prevent recurrences, including resection of lung blebs (either by open surgery or fiberoptic techniques) and 'pleurodesis' (in which the layers of the pleura are fused, usually by insertion of talc or other substances into the intrapleural space). The procedure used depends on many factors, such as the presence of underlying diseases and the availability of techniques.