Tension Pneumothorax in the CST Interview
How to answer a tension pneumothorax scenario in the CST interview: treating before imaging, needle decompression sites, and the definitive chest drain.
On this page
The suddenly breathless, shocked patient after thoracic surgery is the purest ATLS moment in the CST bank: a clinical diagnosis you must treat before any X-ray, in the right order, out loud.
How the scenario tends to open
A typical stem: day one after lung surgery, sudden breathlessness and pleuritic pain; saturations in the eighties, tachycardia, hypotension, absent breath sounds on the operated side, trachea deviated away. The stem hands you the diagnosis — the marks are in what you do with it.
The approach that scores
Name it and explain the physiology in one breath: tension pneumothorax — air trapped under pressure collapsing the lung and obstructing venous return, which is why he is shocked. Then state the rule that defines the station: this is a clinical diagnosis, treated immediately, never delayed for imaging.
- Put out the emergency call and apply high-flow oxygen while you prepare to decompress.
- Decompress at once with a wide-bore cannula on the affected side — current teaching favours the fifth intercostal space in the mid-axillary line, with the older second-space mid-clavicular site as the recognised alternative.
- Say why the site moved: chest-wall thickness and failure rates at the old site — a one-line answer that distinguishes strong candidates.
- State that the needle is a bridge: the definitive step is a chest drain in the safe triangle, inserted with sterile technique, going just above the rib below to spare the neurovascular bundle.
- Reassess from airway onwards after every intervention; on a post-thoracic ward, check the existing drain for kinking, clamping, or blockage; escalate to the cardiothoracic registrar with SBAR and get the post-decompression chest X-ray.
Where candidates lose marks
Requesting a chest X-ray to confirm the diagnosis is the fatal error. The quieter ones: forgetting that needle decompression is temporary, ignoring the existing chest drain that may be the cause, and not reassessing after intervening. If asked whether it could have been caught earlier, answer constructively — trends in observations, learning not blame.
Rehearse it
Reading about tension pneumothorax is the easy half. Rehearse this exact scenario out loud, on the clock, with an AI examiner — this scenario is in Reviva’s library, with feedback marked the way the panel marks. Or start with the wider format in the cst clinical scenarios guide.
Frequently asked questions
- Do you need a chest X-ray to diagnose tension pneumothorax?
- No — it is a clinical diagnosis (deteriorating breathing, absent breath sounds, tracheal deviation, shock) and treatment must come before any imaging. The X-ray follows decompression and drain insertion.
- Where do you needle-decompress a tension pneumothorax?
- Current teaching favours the fifth intercostal space in the mid-axillary line, reflecting failure rates from chest-wall thickness at the older second-space mid-clavicular site — which remains a recognised alternative.
- What comes after needle decompression?
- A chest drain on the same side — the needle is only a bridge. Sterile technique, in the safe triangle, just above the rib below, followed by reassessment and a chest X-ray to confirm position and re-expansion.
Sources. Grounded in the standard (ATLS-style) emergency management of tension pneumothorax as rehearsed in Reviva’s CST clinical scenario. Educational only — follow your local policies and current national guidance.