skip to main content

Arterial transducer levelling — FRCA Primary MCQ

Instant feedback + full explanation. One question, done properly.

HardPhysics and Clinical MeasurementArterial transducer levellingFRCA Primary

An arterial pressure transducer is positioned 20 cm below the right atrium during major vascular surgery. The displayed arterial pressure is higher than expected. What correction is most appropriate?

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

Reveal the answer and explanation

Correct answer: A — Subtract approximately 15 mmHg from the displayed pressure

A pressure transducer below the reference level over-reads because the fluid column adds hydrostatic pressure; 20 cmH2O is about 15 mmHg. The tempting error is to add pressure because the patient appears hypotensive, but the displayed pressure is already falsely high. A normal waveform does not correct for an incorrect zero reference height. The transducer should be levelled to the phlebostatic axis.

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