Question 6

Outline the physiological consequences of a tension pneumothorax. (60% of marks)

Describe the anatomy relevant to the insertion of an intercostal catheter. (40% of marks)

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College Answer

The physiological consequences of tension pneumothorax were in general poorly described.
Purely mentioning clinical features (eg distended neck veins) without an associated physiological
explanation was not sufficient. Good answers described why tension pneumothorax causes
hypoxaemia and hypotension. The cardiovascular mechanism for hypotension and the effect on
pulmonary compliance, pulmonary vascular resistance, lung volumes, work of breathing, shunt
fraction and carbon dioxide elimination should all have been described.
Many candidates used valuable time making comments about tension pneumothorax being a
medical emergency requiring prompt assessment and treatment. These comments attracted no
marks, as they were not sought in the question asked. Often the clinical need for insertion of a
needle/cannula for decompression was mentioned, but again this attracted no marks.
Description of the anatomy relevant to the insertion of an intercostal catheter was very variable.
Most candidates were able to detail the anatomical layers that the catheter had to traverse in order
to gain access to the pleural space, and most explained why the catheter should enter the pleural
space just above the rib. However, few accurately described where access to the pleural space
should be sought and even fewer could explain why. The British Thoracic Society’s ‘safe triangle’
in the axilla and the anatomical boundaries of this were correctly described by very few candidates.
No candidate described an anterior approach through the mid clavicular line, although anatomical
details of this approach would have been acceptable.