Management of pneumothorax

It is important to recognise the signs of pneumothorax, say Dr Suneeta Kochhar and Dr Paul Cornelius.

Pneumothorax is defined as air in the pleural space and may be classified as spontaneous, traumatic or iatrogenic. Primary spontaneous pneumothorax occurs in patients without clinically apparent lung disease; secondary spontaneous pneumothorax is a complication of pre-existing lung disease.1

Primary pneumothorax has an incidence of 18-28 per 100,000 per year for men and 1.2-6 per 100,000 per year for women.2 Primary pneumothorax typically occurs in tall, thin males between the ages of 10 and 30 years with a recurrence rate of approximately 30 per cent.1

The incidence of secondary spontaneous pneumothorax is similar to that of primary spontaneous pneumothorax; however, the peak incidence occurs between 60-65 years.

Chest X-ray showing bullae: the mechanism of formation is unclear

Chest X-ray showing right-sided pneumothorax

Aetiology
Smoking increases the risk of pneumothorax in a dose-dependent manner. The lifetime risk of developing a pneumothorax in healthy male smokers may be as high as 12 per cent compared with 0.1 per cent in non-smokers.1

Subpleural blebs and bullae play a role in the pathogenesis as they are found in up to 90 per cent of patients with primary pneumothorax at thorascopy or thoracotomy and in up to 80 per cent of cases following CT scanning of the chest.3

The gradient in pleural pressure increases from the lung base to the apex, therefore alveoli at the lung apex in tall individuals are subject to a greater distending pressure than those at the base of the lung. This means there is an increased risk of developing subpleural blebs.

The mechanism of bulla formation is unclear. It has been suggested that there is degradation of elastic fibres in the lung as a result of a smoking-related influx of neutrophils and macrophages. Moreover, after bullae have formed, inflammation-induced obstruction of small airways increases alveolar pressure, resulting in an air leak into the lung interstitium.1

Secondary spontaneous pneumothorax occurs in patients with underlying pulmonary disease. COPD and Pneumocystis carinii pneumonia infection in HIV-positive patients are the most common associated conditions,2 and so this diagnosis should be considered in patients with these conditions who present acutely short of breath.

Patients with an FEV1 <1 litre or an FEV1 to FVC ratio of less than 40 per cent are at greatest risk. Other causes include interstitial lung disease such as sarcoidosis and Langerhans' cell histiocytosis.1

Clinical presentation
Most patients present with ipsilateral pleuritic chest pain and acute shortness of breath. Shortness of breath is largely dependent on the size of the pneumothorax and whether there is underlying chronic lung disease.

Young patients may have chest pain only. Most episodes of pneumothorax occur at rest. Symptoms may resolve within 24 hours in patients with primary spontaneous pneumothorax.

Patients with a very small pneumothorax may have a normal physical examination. Tachycardia may result. With a large pneumothorax clinical findings include decreased movement of the chest wall, hyper-resonance on percussion and decreased or absent breath sounds on the affected side.

Tension pneumothorax is a life-threatening condition requiring emergency treatment. It therefore needs to be considered in any patient with severe acute respiratory distress.3 It is a clinical diagnosis requiring immediate treatment with needle thoracocentesis.

The diagnosis of a pneumothorax is confirmed by finding a visceral pleural line displaced from the chest wall, without distal lung markings, on a posterior-anterior chest radiograph.

Expiratory chest radiographs are not recommended for the routine diagnosis of pneumothorax. A lateral chest or lateral decubitus radiograph may be performed if there is a high index of suspicion of a pneumothorax. The main indication for CT is to distinguish an emphysematous bulla from a pneumothorax.4

A large pneumothorax results in a decreased vital capacity, ventilation-perfusion mismatch and shunting resulting in hypoxaemia. Arterial blood gas measurements may show a respiratory alkalosis.

The size of the pneumothorax is classified as small or large depending on whether there is a visible rim <2cm or [s40] 2cm between the lung margin and the chest wall on a radiograph.2

It has been estimated that a 2cm radiographic pneumothorax occupies 49 per cent of the hemithorax. The management of pneumothorax aims to remove air from the pleural space and prevent recurrences.

Primary pneumothorax
In small pneumothoraces with minimal symptoms, no active treatment is required.

These patients can be safely discharged with early outpatient review and should be given written advice to return if breathlessness worsens.

Patients who have been discharged without intervention should be advised that air travel should be avoided until a radiograph has confirmed resolution of the pneumothorax.5

If a patient requires overnight observation, high flow oxygen is administered. Inhalation of high concentrations of oxygen may reduce the total pressure of gases in pleural capillaries by reducing the partial pressure of nitrogen. During oxygen supplementation there may be an increase in the rate of pneumothorax reabsorption.

Breathless patients should not be left without intervention regardless of the size of pneumothorax. If there is a rim of air >2cm on the chest X-ray, this should be aspirated.2

Aspiration is successful in approximately 70 per cent of patients; the patient may be discharged subsequently. A further attempt at aspiration is recommended if the patient remains symptomatic and a volume of less than 2.5 litres has been aspirated on the first attempt.

If unsuccessful, an intercostal drain is inserted. This may be removed after 24 hours after full re-expansion or cessation of air leak without clamping and discharge may be considered.5

If this fails, a referral to a chest physician within 48 hours is recommended.

Secondary pneumothorax
For patients with a secondary pneumothorax dyspnoea may be more severe as respiratory reserve has already been reduced.

This is often out of proportion to the size of the pneumothorax. If small secondary pneumothoraces are less than 1cm depth or there are isolated apical pneumothoraces in an asymptomatic patient, observation only may be appropriate.2

These patients need admission because of the risk of respiratory compromise. Active treatment of the underlying lung disorder is important.

If patients are breathless and over the age of 50 and/or there is a rim of air >2cm on the chest X-ray, an intercostal chest drain is recommended.

Simple aspiration is less likely to succeed in secondary pneumothoraces. Successful re-expansion of the lung is between 33-67 per cent in comparison with 59-83 per cent success achieved in primary pneumothoraces.5

In patients under 50 with a rim of air <2cm on chest X-ray, aspiration may be an option if there is minimal shortness of breath.

Surgical intervention
Open thoracotomy and pleurectomy remains the procedure with the lowest recurrence rate for difficult or recurrent pneumothoraces. Indications for surgery include second ipsilateral pneumothorax, first contralateral pneumothorax, bilateral spontaneous pneumothorax, persistent air leak, spontaneous haemothorax and professions at risk, such as pilots and divers.

VATS is associated with better outcomes and seems to have a complication profile comparable with that of thoracotomy for the treatment of pneumothorax.6

Dr Kochhar is an A&E SHO on GP rotation and Dr Cornelius is an A&E consultant at the Conquest Hospital, Hastings

References
1. Sahn S, Heffner J. Spontaneous pneumothorax. N Engl J Med 2000; 342: 868-74.

2. Henry M, Arnold T, Harvey J. BTS guidelines for the management of spontaneous pneumothorax. Thorax 2003; 58 (Suppl II): ii39-ii52.

3. Tschopp J, Rami-Porta R, Noppen M, Astoul P. Management of spontaneous pneumothorax: state of the art. Eur Respir J 2006; 28: 637-50.

4. O'Connor A, Morgan W. Radiological review of pneumothorax. BMJ 2005; 330: 1,493-7.

5. Baumann M. Management of spontaneous pneumothorax. Clin Chest Med 2006; 27: 369-81.

6. Sedrakyan A, van der Meulen J, Lewsey J, Treasure T. Video assisted thoracic surgery for the treatment of pneumothorax and lung resections: systematic review of randomised clinical trials. BMJ 2004; 329: 1,008-12.

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