Spirometry: performing and explaining the test
PLAB 2 & PRES 3 · practical skills / respiratory · medium · 8 minutes
Candidate brief
You are an FY2 doctor in a GP respiratory clinic. Mr Peter Novak, 61, has been referred for spirometry to investigate two years of progressive breathlessness and chronic cough. He is an ex-smoker. Please perform spirometry with him, explaining the test and coaching him through it, then explain the results and the next steps. Verbalise your checks and reasoning as you go.
What examiners look for
Spirometry is a coached performance, not a blood pressure reading: the quality of the blow is the quality of the result. A hesitant start underestimates FEV1, a first-second cough invalidates the blow, and stopping at three seconds shrinks the FVC and falsely normalises the ratio. Examiners mark the coaching as much as the interpretation. Quality has numbers: at least three acceptable manoeuvres, with the best two FEV1 and FVC readings within about 150 ml of each other. If you cannot say your traces were acceptable and repeatable, you do not yet have a result — you have an attempt. The contraindication screen exists because a maximal forced exhalation is a Valsalva-like stress: intrathoracic, intra-abdominal, intraocular and intracranial pressures all spike. Recent infarction, pneumothorax, recent eye or abdominal surgery and haemoptysis are the questions that stop a routine test becoming an incident. Pre- versus post-bronchodilator is a diagnostic boundary, not a detail: COPD is defined by a post-bronchodilator FEV1/FVC ratio below 0.7 in the right clinical context. Today's pre-bronchodilator 0.61 makes obstruction likely — it does not complete the diagnosis, and a candidate who books the COPD label on it has overcalled the test. What the patient took this morning is part of the test conditions. Bronchodilators shortly before diagnostic spirometry blunt exactly the reversibility and baseline you are trying to measure; noticing, recording and acting on it (proceed with caveat, or reschedule per protocol) is what separates a measurement from a guess. Whatever the trace shows, the highest-yield intervention in this man's future is already achieved — he stopped smoking — and saying so warmly, before discussing inhalers and rehabilitation, is the consultation skill inside the practical skill.
Guideline references
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