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Underdamped arterial pressure trace — FRCA Primary MCQ

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HardPhysics and Clinical MeasurementUnderdamped arterial pressure traceFRCA Primary

A pressure transducer attached to an arterial line is flushed and released. The waveform oscillates several times before returning to baseline, and systolic pressure appears falsely high while diastolic pressure appears falsely low. What is the most likely problem?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: B — Overdamping from an air bubble

Underdamping produces overshoot and ringing, causing overestimated systolic and underestimated diastolic pressures. Air bubbles, clots and compliant tubing more commonly cause overdamping with a blunted waveform. Incorrect levelling shifts the whole pressure reading rather than producing ringing. The clinical pearl is that waveform quality must be assessed before acting on extreme numbers.

Reference: RCoA Primary FRCA Syllabus 2026; Davis and Kenny Basic Physics and Measurement in Anaesthesia