Arterial Line - Square Wave Test 

The arterial line can measure BP inaccurately unless properly calibrated. Rapidly flushing the line (by pulling the release on the flush device) generates a square wave. Counting oscillations after the square wave indicates if the arterial line is working properly.

Normal = accurate BP

    - 1.5 - 2 oscillations

OVERdamped = falsely LOW BP

    - <1.5 oscillations

    - Absence of dicrotic notch

    - Fix: Remove extra tubing & any air bubbles.

UNDERdamped = falsely HIGH BP

    - >2 oscillations

    - Additional artifactual spikes

    - Fix: Adjust filter settings on monitor



Nick Mark MD @nickmmark



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