Contents
Introduction
A pneumothorax is an abnormal collection of air in the pleural space – between the lung and the chest wall. They can be:
- Primary – no underlying lung disease.
- Secondary – to underlying lung disease – such as COPD
They can also separately be classified as spontaneous or traumatic.
The majority of cases of spontaneous pneumothorax are minor and will self resolve, but in a small number of cases, a one way valve can form, allowing more and more air into the pleural space. We call this a tension pneumothorax and it is a medical emergency. Left untreated, a tension pneumothorax is fatal.
Epidemiology and Aetiology
Primary Spontaneous Pneumothorax (PSP)
- Usually the result of rupture of a pleural “bleb” – the bleb is often from congenital defect in the tissue of the alveolar wall.
- These blebs are more common in tall young men
- Rare – incidence from 4 – 40 per 100,000 per year
- More common in men – M:F is around 2.5:1
- Recurrence rate of 25-50% – usually recur within the first year
- Patients typically in their 20’s – rare after age of 40
- Risk factors inlude
- Smoking (including smoking cannabis) – about 90% of cases occur in smokers – smoking probably increases the risk by causing airway inflammation. The risk is proportional to the amount smoked
- Family history – 25% of cases have an associated FHx
- Marfan Syndrome
- Homocystinurea
- A tension pneumothorax occurs in about 1-2% of cases
Secondary Pneumothorax
Causes include
- COPD
- Cystic fibrosis
- Lung malignancy
- Pneumonia
- TB
Presentation
- Are often similar acute events, whether or not they are primary or secondary
- Symptoms typically develop at rest
- Sudden onset shortness of breath and pleuritic chest pain – usually on the side of the pneumothorax
- Symptoms often proportional to the size of the pneumothorax
- Reduced breath sounds on affected size
- Hyperresonance to percussion on affected side
- Hypoxia
- Hypercapnia is not usually present
- Symptoms are often more severe in secondary pneumothorax – presumably due to the reduced reparatory reserve seen in underlying lung disease
A pneumothorax can be can be divided into:
Standard or simple pneumothorax
- Air in the pleural space, but the volume is not increasing.
- On CXR: trachea is not deviated. Lung collapse may be visible (sometimes subtle – decreased vascular markings around the outer lung field)
Tension pneumothorax – LIFE THREATENING
- Air in the pleural space, and the volume continuing to increase. Typically due to the formation of a one-way valve, allowing air into the pleural space on inspiration, but not out again on expiration.
- On CXR – the trachea may be deviated away from the side of the pneumothorax. Lung collapse likely to be more obvious.
- A tension pneumothorax causes rapidly increases intra-thoracic pressure. This reduces venous return to the heart and causes cardiac arrest if not treated quickly.
Clinical features of a Tension Pneumothorax:
- Plueritic chest pain
- Breathlessness
- Tracheal deviation
- Reduced breath sounds in the affected area and hyper-resonant on percussion
Note that these features may not be present – and when they are present are a very late sign – the patient is likely to be peri-arrest!
Differentiating a simple pneumothorax from a tension pneumothorax
A tension pneumothorax will have:
- Worsening clinical signs and symptoms (simple will be stable)
- Tracheal deviation
- Haemodynamically unstable
- Hypotensive
- Tachycardic
- Elevated respiratory rate
Complications
Compression of the mediastinum = Decrease Cardiac Output (compressed heart) , increase Heart Rate, jugular vein distension, cardiac arrest
Investigations
Often a clinical diagnosis. A tension pneumothorax should be a clinical diagnosis – in a truly life threatening situation there is no time to wait for an x-ray! The x-ray of a tension pmneumothorax is sometimes referred to as “the x-ray you never want to see” – because ideally it should have been diagnosed and treated beforehand.
Chest X-ray and CT
Pneumothoraxes are equally visible on inspiratory and expiratory chest x-rays. A standard inspiratory film is all that is usually required.
Typically, pneumothoraxes are small, and often appear as a ‘rim’ of air around the lung. It is often possible to see a white line which represented the edge of the normal lung tissue. Externally to this, there will be NO vascular lung markings.
Larger pneumothoraxes are more obvious, with a clearly collapsed lung, and a large proportion of the hemithorax with no vascular margins. Check for mediastinal shift (which would indicate the presence of a tension pneumothorax). The absence of mediastinal shift does not eclude a tension pneumothorax – and the diagnosis is often clinical (signs of haemodynamic instability), as it often not possible to tell the difference on x-ray findings alone.
Check for any underlying lung disease to differentiate between a primary and secondary pneumothorax.
Indications for CT
- Evidence of underlying lung disease on CXR
- Uncertain diagnosis
- Not routinely indicated
A large bleb / emphysematous bullae may mimic a pneumothorax, making diagnosis unclear. In these cases consider CT scan. If there is an uncertain diagnosis and there isn’t a pneumothorax – you will cause one by attempting a decompression!
Ultrasound
Although not a routine investigation, the use of bedside ultrasound is becoming more common, particularly in the acute setting – for example in the emergency department (with or without trauma) or in intensive care.
Signs on USS include absence of ‘lung sliding’ (at the interface of the lung and the pleura).
Bedside USS is highly operator dependent.
Studies of USS have shown it to be more sensitive than chest x-ray for diagnosis of pneumothorax.
Blood Gas
- Hypoxia
- Usually normal carbon dioxide – the lung function is still good and often the remaining normal lung can provide sufficient alveolar ventilation – but can be low
- Respiratory alkalosis – can occur if there is sufficient hyperventilation to cause low carbon diaxoide. This hyperventilation can be due to a combination of hypoxia, anxiety and pain
Emergency Pneumothorax Treatment
Standard Pneumothorax – should do CXR first before attempting to treat!
Rim of air <2cm – consider alternate diagnosis, OR small pneumothorax that will resolve with conservative management.
- Consider observation for 4-6 hours and repeat CXR to ensure it is not progressing
- Then; discharge on advice – dont do strenuous exercise – and return if breathless.
- Evaluate and re-x-ray at 2 weekly intervals until air is re-absorped
- The rate of reabsorption is approximately 1-2% of the volume of the hemithroax per 24 hours. This can be increased to 6-8th with the use of humidified oxygen
- It is recommended that patient avoid air travel for at least 2 weeks after resolution. The exact risks are not known
Primary Pneumothorax – SOB + rim of air >2cm on CXR:
- Give supplemental oxygen
- If acutely unwell (i.e. haemdynamically unstable), or tension pneumothorax:
- Attempt aspiration – 2ND INTERCOSTAL SPACE, MIDCLAVICULAR LINE!
- If unsuccessful, repeat
- If unsuccessful, consider chest drain
- Once successfully decompressed, will need a chest drain to allow continuing decompression
- If not haemodynamically unstable:
- Chest Drain (can be traditional thoracotomy or ‘pig-tail’ catheter (becoming more common – same equipment used as in supra-pubic catheter – therefore involves seldinger technique, is a less invasive procedure)
- Remember to connect the chest tube to a water seal device – and check that the water ‘swings’ (rises and falls) with each breath – this confirms correct placement of the tubs within the pleural space
- Chest Drain (can be traditional thoracotomy or ‘pig-tail’ catheter (becoming more common – same equipment used as in supra-pubic catheter – therefore involves seldinger technique, is a less invasive procedure)
- Refer to ICU if appropriate and admit to hospital
Secondary Pneumothorax – SOB + rim of air >2cm on CXR
- As above
- Treat any underlying cause as appropriate
- More likely to be hospitalised – because more likely to be unwell, and also because they may need treatment of the underlying condition and / more likely to require a pleurodesis
Tension Pneumothorax
- If suspected, attempt to aspirate before CXR. Use a large bore cannula and, if possible with syringe, filled with saline, to act as a water seal, when entering the pleural space.
- You should attempt decompression at the 2nd intercostal space at the mid-clavicular line. Feeling for this is sometimes a bit tricky – it is roughly 2 finger widths below the clavicle
- Use a long needle – preferable a cannula about 8cm or longer. Needle decompression fails in up to 50% of patients – often because too short of a needle is used. The typical distance from skin to pleura in an adult male is about 5cm
- You should go in just above the third rib, so as to avoid the neurovasuclar bundle below the second rib.
- Needle decompression is only a temporary measure – a chest tube should be placed as soon as possible. In a non-tension pneumothorax a chest drain is often the first line treatment of choice.
- Needle decompression is suprisingly ineffective – one study suggested it was only about 67% effective at decompression, compared to over 90% for the placement of a chest tube. As such, a chest tube is preferred if circumstances allow, however it takes longer (mainly getting set up with all equipment . scrubbing up etc). If you are in doubt, do a needle aspiration first (you might save the patient’s life) and follow-up with a chest drain.
If pneumothorax remains at 48 hours or patient has recurrent episodes then consider pleurodesis (VATS procedure).
References
Primary Spontaneous Pneumothorax in Adults – UpToDate