An intra-arterial blood pressure trace appears rounded with loss of the dicrotic notch, and after a fast-flush test the trace returns slowly to baseline without any oscillations. Compared with the true arterial pressure, this system will:

• A Overestimate systolic and underestimate diastolic pressure
• B Overestimate both systolic and diastolic pressures
• C Underestimate systolic and overestimate diastolic pressure ✓
• D Record accurate mean pressure only when underdamped

Explanation

The absent oscillations after the square-wave flush indicate an overdamped system. Damping blunts the systolic peak and elevates the diastolic trough, so systolic pressure is underestimated and diastolic pressure overestimated. The mean pressure remains relatively accurate because it depends on area under the curve rather than waveform shape. Common causes are air bubbles, clots in the cannula, excessive tubing length and kinks. Underdamping produces the opposite error with exaggerated systolic overshoot and ringing.

Reference: Miller's Anesthesia, 9th ed.

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