Arterial Line Dynamic Response Testing

Created on Mon, 06/29/2015 - 18:00
Last updated on Mon, 06/29/2015 - 18:00

Dynamic Response is a function of Natural Resonant Frequency and Damping Coefficient

The Natural Resonant Frequency: How fast the system vibrates in response to a pressure signal

The Damping coefficient: How quickly those vibrations come to rest in the system

The Square Wave Test

When you squeeze the fast flush valve, you let the transducer taste some of the 300mmHg in the pressurized saline bag. This produces a waveform that rises sharply, plateaus, and drops off sharply when the flush valve is released again.

This is the "square wave".

The accurate, responsive, adequately damped arterial line waveform

normally damped arterial line waveform

A good art line trace has a distinct dicrotic notch, and after the fast flush test there are two oscillations only.

The over-damped arterial line waveform

Overdamped arterial line waveform

The over-damped trace will lose its dicrotic notch, and there wont be more than one oscillation.
This happens when there is clot in the catheter tip, or an air bubble in the tubing.

The under-damped arterial line waveform

Underdamped arterial line waveform

The under-damped trace will overestimate the systolic, and there will be many post-flush oscillations.

The MAP remains the same in spite of damping.

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References

From Bersten and Soni's" Oh's Intensive Care Manual", 6th Edition; plus McGhee and Bridges Monitoring Arterial Blood Pressure: What You May Not Know (Crit Care Nurse April 1, 2002 vol. 22 no. 2 60-79 )

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