Pneumothorax occurs when air gets into the pleural space separating the lung from the chest wall. It can occur spontaneously or secondary to trauma, medical interventions (“iatrogenic”) or lung pathology. The typical patient in your exams is a young, tall, thin young man presenting with sudden breathlessness and pleuritic chest pain, possibly whilst playing sports.


  • Spontaneous
  • Trauma
  • Iatrogenic such as due to lung biopsy, mechanical ventilation or central line insertion
  • Lung pathology such as infection, asthma or COPD


Chest Xray

Erect chest xray is the investigation of choice for a simple pneumothorax.

A chest xray will show an area between the lung tissue and the chest wall where there are no lung markings. There will be a line demarcating the edge of the lung where the lung markings ends and the pneumothorax begins.

Measuring the size of the pneumothorax on a chest xray can be done according to the BTS guidelines from 2010. This involves measuring horizontally from the lung edge to the inside of the chest wall at the level of the hilum.

CT thorax can detect a small pneumothorax that is too small to see on a chest xray or be used to accurately assess the size of the pneumothorax.



This is based on the 2010 guidelines from the British Thoracic Society:

  • If no SOB and there is a < 2cm rim of air on the chest xray then no treatment required as it will spontaneously resolve. Follow up in 2-4 weeks is recommended.
  • If SOB and/or there is a > 2cm rim of air on the chest xray then it will require aspiration and reassessment.
  • If aspiration fails twice it will require a chest drain.
  • Unstable patients or bilateral or secondary pneumothoraces generally require a chest drain.


Tension Pneumothorax

Tension pneumothorax is caused by trauma to chest wall that creates a one-way valve that lets air in but not out of the pleural space. The one-way valve means that during inspiration air is drawn into the pleural space and during expiration, the air is trapped in the pleural space. Therefore more air keeps getting drawn into the pleural space with each breath and cannot escape. This is dangerous as it creates pressure inside the thorax that will push the mediastinum across, kink the big vessels in the mediastinum and cause cardiorespiratory arrest.

Signs of Tension Pneumothorax

  • Tracheal deviation away from side of pneumothorax
  • Reduced air entry to affected side
  • Increased resonant to percussion on affected side
  • Tachycardia
  • Hypotension


Management of Tension Pneumothorax

The management sentence you need to learn and recite in your exams is: “Insert a large bore cannula into the second intercostal space in the midclavicular line.”

If a tension pneumothorax is suspected do not wait for any investigations. Once the pressure is relieved with a cannula then a chest drain is required for definitive management.


Chest Drain

Chest drains are inserted into the “triangle of safety”. This triangle is formed by:

  • The 5th intercostal space (or the inferior nipple line)
  • The mid axillary line (or the lateral edge of the latissimus dorsi)
  • The anterior axillary line (or the lateral edge of the pectoris major)

The needle is inserted just above the rib to avoid the neurovascular bundle that runs just below the rib. Once the chest drain is inserted obtain a chest xray to check the positioning.


Last updated March 2019
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