Pneumothorax

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Introduction

A pneumothorax is a collection of air inside the pleural space, which is the space between the lungs and chest wall (Figure 1).

A primary pneumothorax occurs in a patient without a known respiratory disease, whereas a secondary pneumothorax occurs in a patient with pre-existing respiratory disease.

A tension pneumothorax is a severe pneumothorax involving the displacement of mediastinal structures and haemodynamic compromise.1

In the UK, the incidence of pneumothorax is 19 per 100,000 in males and 8 per 100,000 in females. 85% of pneumothoraces are primary, and incidence is highest in patients aged over 65.2-3

You might also be interested in our medical flashcard collection which contains over 1000 flashcards that cover key medical topics.
The pleural space
Figure 1. The pleural space.4

Aetiology

Causes of primary pneumothorax include:

  • Often unknown
  • May be due to rupture of a subpleural air bleb (found in the pleural space). The bleb itself is caused by alveolar rupture, which lets air travel through the interlobular septum into the subpleural space.5

Causes of secondary pneumothorax include:

  • Chronic obstructive pulmonary disease (70% of secondary pneumothorax): rupture of air bulla (air-filled space in lungs, caused by emphysematous destruction of lung tissue).6-7
  • Asthma: rupture of air bulla or subpleural air bleb, though the mechanism is still poorly understood.8
  • Cystic fibrosis: endobronchial obstruction causing increased pressure in the alveoli, leading to alveolar rupture.9
  • Marfan syndrome: abnormal lung connective tissue leads to increased formation of air bulla (which rupture), and tall body habitus increases mechanical stress on lung apices (exacerbating bulla rupture).10

Causes of tension pneumothorax include:11

  • Penetrating/blunt trauma
  • Mechanical ventilation or non-invasive ventilation (NIV)
  • Conversion of simple pneumothorax to tension pneumothorax

Pathophysiology

The alveolar and atmospheric pressures are greater than the intrapleural pressure. Therefore, connections between the alveoli and pleural space, or surrounding atmosphere and pleural space, will lead to air moving down a pressure gradient into the pleural space.

This increases the intrapleural pressure, potentially compressing the lungs. Air will continue to move into the pleural space until the pressure gradient equilibrates or the connection into the pleural space seals off.12

In a tension pneumothorax, air enters the pleural space through a one-way valve and is therefore unable to leave the pleural space. The intrapleural pressure exceeds the atmospheric pressure, leading to collapse of the ipsilateral lung and a shift of the mediastinum away from the pneumothorax.

In severe cases, the increased intrapleural pressure can compress the heart and surrounding vasculature, reducing cardiac output and venous return. If untreated, this may lead to cardiac arrest.1


Risk factors

Risk factors for pneumothorax include:

  • Smoking
  • Tall and thin build
  • Male sex
  • Young age (in primary pneumothorax)

Clinical features

History

A small pneumothorax may be asymptomatic.13

Typical symptoms of pneumothorax include:

  • Ipsilateral pleuritic chest pain
  • Dyspnoea
  • Cough

Other important areas to cover in the history include:

  • Recent trauma to the chest wall
  • Smoking history: quantify in pack-years (1 pack-year equates to smoking 20 cigarettes a day for a whole year)
  • Family history of pneumothorax

Clinical examination

A full respiratory examination should be performed in suspected cases of pneumothorax.

Typical clinical findings in pneumothorax include (on the same side as the pneumothorax):

  • Hyper-resonant lung percussion
  • Reduced breath sounds
  • Reduced lung expansion

In addition, typical clinical findings in tension pneumothorax include:

  • Tracheal deviation away from the pneumothorax
  • Severe tachycardia
  • Hypotension

Differential diagnoses

The presenting complaints of pneumothorax have important differential diagnoses. Table 1 outlines these differential diagnoses, and the features which differentiate them from pneumothorax.

Table 1. Differential diagnoses of pneumothorax.

Differential diagnosis Features differentiating from pneumothorax

Acute asthma exacerbation

  • Expiratory wheeze
  • Trial of bronchodilator relieves symptoms
  • CXR: usually normal

Pleural effusion

  • Stony dull percussion
  • Chest pain may ease as effusion continues to enlarge, as the visceral and parietal pleural move apart (and so there is less rubbing between the pleura, which is the cause of the pleuritic chest pain)14
  • CXR: pleural effusion

Pulmonary embolism

  • Unilateral calf swelling/tenderness (DVT)
  • Risk factors for PE (e.g. recent immobility)
  • CTPA: pulmonary embolism

Myocardial infarction

  • Classically described as crushing chest pain (rather than pleuritic)
  • Radiates to neck/arm
  • ECG: signs of ischaemia (e.g. ST elevation)

Investigations

Bedside investigations

Relevant bedside investigations include:

  • Pulse oximetry
  • Lung ultrasound: used in supine trauma patients, for whom a chest X-ray may be difficult to obtain. The characteristic finding is an absence of lung sliding. Lung sliding is caused by the visceral pleura moving back and forth on the parietal pleural. This is absent in pneumothorax as there is air separating the visceral pleura from the parietal pleura.15

Laboratory investigations

Relevant laboratory investigations include:

  • Full blood count: important in trauma cases, as the patient may need a blood transfusion
  • Clotting screen: may need to correct coagulopathy (such as INR >1.5 or platelets <50), although this may not be possible in tension pneumothorax.16
  • Arterial blood gas (ABG): the most common finding is respiratory alkalosis secondary to hyperventilation, but it may demonstrate type 1 respiratory failure in severe cases.

Imaging investigations

Relevant imaging investigations include:

  • Chest X-ray (Figures 2 and 3): visible rim between the lung margin and chest wall, with an absence of lung markings. The size of the pneumothorax is measured at the level of the hilum: >2cm is classified as a “large” pneumothorax.17
  • CT chest (Figure 4): may be used to identify small pneumothoraces missed by chest X-ray. Also, can help to identify the cause of the pneumothorax (can show air bulla or emphysematous changes).

 


Management

For more information on the emergency management of pneumothorax, see the Geeky Medics guide to the acute management of pneumothorax using an ABCDE approach. 

Simple (non-tension) pneumothorax

Figure 5 outlines the management of a simple pneumothorax.

A large (>2cm) pneumothorax causing minimal symptoms may be managed conservatively in certain patients (this is a senior-led decision). If needle aspiration fails, a small-bore chest drain (<14 French) is required.

Pneumothorax management flowchart
Figure 5. Pneumothorax management, adapted from the British Thoracic Society guidelines.17
Chest drain insertion

If a chest drain is inserted, look out for:

  • Swinging: the fluid in the chest drain tubing moves towards the patient during inspiration (due to reduced intrathoracic pressure during inspiration when the diaphragm descends).
  • Bubbling: the fluid in the chest drain bottle bubbles when the pneumothorax is initially drained (this should stop eventually). The persistence of bubbling for >48 hours may indicate an air leak, which is a connection between the bronchial tree and pleural space (also known as a bronchopleural fistula).21 This may need to be discussed with a thoracic surgeon.

Tension pneumothorax

Management of tension pneumothorax should include:

  1. Emergency decompression: insert a large-bore cannula (e.g. orange 14G or grey 16G) into the 2nd intercostal space, along the mid-clavicular line
  2. Chest drain insertion immediately after emergency decompression

Follow up

In general, patients should have outpatient respiratory follow-up and a repeat chest X-ray in 2-4 weeks to assess for the resolution of pneumothorax. They should be advised not to fly until full resolution of the pneumothorax.

A recurrent/difficult pneumothorax may need an open thoracotomy and pleurectomy. The parietal pleural is usually removed, and so the lung sticks to the inner surface of the chest wall, preventing pneumothorax recurrence.22

Medical pleurodesis may be needed in patients unfit for surgery. This involves inserting a chemical (such as tetracycline or talc), which obliterates the space between the visceral and parietal pleura, preventing pneumothorax recurrence.23


Complications

Disease-related complications of pneumothorax include:

  • Respiratory failure
  • Cardiac arrest (in tension pneumothorax)
  • Pneumopericardium (air in the pericardial space)

Treatment-related complications of pneumothorax include:

  • Pain
  • Re-expansion pulmonary oedema: typically occurs after drainage of a large pneumothorax that has been present for >72 hours. Rapid re-expansion of a previously collapsed lung can lead to increased permeability of pulmonary vessels, for unknown reasons.24 This leads to fluid moving into the lung parenchyma, causing pulmonary oedema.
  • Subcutaneous emphysema: when the chest drain is inserted into the subcutaneous tissue, rather than the pleural space

Key points

  • A pneumothorax involves the presence of air within the pleural space.
  • A primary pneumothorax (patient with no lung conditions) is usually due to rupture of a subpleural air bleb; a secondary pneumothorax (patient with a lung condition) is typically due to a variety of interlinked factors.
  • The main presenting complaints of pneumothorax are ipsilateral chest pain and dyspnoea.
  • Diagnosis is based on a chest X-ray or CT scan.
  • Management of pneumothorax depends on its size and whether it is primary or secondary in aetiology.
  • Tension pneumothorax requires immediate decompression and insertion of a chest drain.
  • Complications of pneumothorax include respiratory failure and re-expansion pulmonary oedema.

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Reviewer

Dr Neeraj Shah

Specialist registrar in Respiratory Medicine


Editor

Dr Chris Jefferies


References

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