Anaes Cases · Anaesthesia / physics & measurement — invasive pressure monitoring

Systolic of 240 with a flickering arterial trace — the under-damped arterial line

The hot case — the classic pressure-measurement crisis: an under-damped arterial line producing a spurious systolic hypertension (242 vs the cuff's 148), risking iatrogenic hypotension if an antihypertensive is given. The recognition (the ringing waveform, the cuff discrepancy, the wide pulse pressure), the immediate management (do NOT treat the number; run a fast-flush square-wave test; recognise the many oscillations of under-damping; remove air bubbles, shorten and stiffen the tubing, re-zero and re-level), and the physics that explains why under-damping distorts systolic high and diastolic low but preserves the MEAN — the single most examined pressure-measurement scenario. Includes the comparison with over-damping (slurred, under-read systolic) and the levelling and zeroing checks, and the clinical decision that the true pressure (mean 119, cuff 148/78) does not require an antihypertensive.