Arterial line damping and misleading hypotension — FFICM MCQ

Correct answer: D — Troubleshoot and re-zero the arterial line system before escalating vasopressors

The correct answer is D, troubleshoot and re-zero the arterial line system before escalating vasopressors. The stem shows classic evidence of a technical artefact rather than true hypotension: a damped waveform, an underpressurised flush bag, blood in the tubing, and a cuff reading well above the arterial trace, in a patient with warm peripheries, good urine output and falling lactate confirming adequate perfusion. An overdamped arterial system (clot, air, kinking, low flush pressure) characteristically underestimates systolic pressure, explaining the discrepancy without any real deterioration. Standard practice is to confirm correct zeroing and levelling of the transducer, perform a square wave (fast flush) test, and clear clot, air or kinks before trusting the readings to guide vasopressor therapy. Why the other options are wrong: A, Increase noradrenaline based solely on the arterial number: this ignores clear clinical evidence of adequate perfusion and treats an artefactual figure as real, risking harmful over-vasoconstriction and end-organ ischaemia. B, Give thrombolysis for line clot: thrombolysis is never used for a peripheral arterial cannula; a suspected clot is managed by aspiration and flushing or resiting the line, not thrombolytic drugs. D, Remove blood pressure monitoring: abandoning invasive monitoring in a noradrenaline-dependent postoperative patient discards essential beat-to-beat data; the fault is in the system, not the indication for monitoring, so it should be corrected, not removed. E, Treat as cardiac tamponade: warm hands, good urine output and falling lactate are reassuring perfusion markers inconsistent with obstructive shock, so tamponade is not supported here. Key point: an overdamped or faulty arterial line can give artefactually low pressures, so technical troubleshooting must precede any vasopressor change when clinical perfusion markers remain reassuring.

Reference: Intraoperative Invasive Blood Pressure Monitoring and the Potential Pitfalls of Invasively Measured Systolic Blood Pressure, PMC (2021), https://pmc.ncbi.nlm.nih.gov/articles/PMC8483407/