Arterial Line Question - page 4

by wonderbee

I'm precepting in CVICU which so far has been great. I'm curious about how an arterial line works. I understand what it's for, but don't understand how it works. Is pressure going through the line to keep the vessel open?... Read More

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    Well, you're not actually flushing the line when you zero, you're doing a square wave test. For this, you pull on/push on (depending on the brand of transducer you have) the fast-flush device briefly while watching the waveform on the monitor. You should see a "square wave" where the waveform rises, flattens out for a space then rapidly returns to the baseline with minimal zig-zagging at the baseline. This tells you that your line is optimally damped. This means that you have the scale for the pressure being monitored set correctly and thus your waveforms will be useful and accurate. If you see a slower response with more blunt waves, then your transducer is "overdamped" or the scale set on the monitor is too high. Obviously then, if there's a big bounce at the end when you let go of your fast-flush, the transducer is "underdamped"- the scale is set too low. (Or there may be a small thrombus forming at the tip of your catheter, but you're unlikely to be fixing that on your own.)

    Zeroing is the act of calibrating the transducer to the atmospheric pressure. It's the quality control measure that allows you to feel justified in believing the numbers on the monitor. You want to ensure that the transducer is reading the pressure accurately so you remove the effect of the atmosphere from the equation when you zero. Weather is about the only thing that alters the atmospheric pressure in your patient's room. Repositioning the patient, raising or lowering their head, raising or lowering the bed - nope. But those things do change the phlebostatic axis - the position of the right atrium of the heart - our reference point for leveling. So make sure you adjust the level of the transducer accordingly; you'll only need to zero once a shift unless the weather changes!
    Hawkeye-RN likes this.
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    Thank you so much for this useful information. If you don't mind, I just have one more question: Should I do the square wave test in conjunction with zeroing? Does one interfere with the other? Which one should be done first? I undrstand how often the zeroing should be done; does that apply to the square wave test also?
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    You can't do them both at the same time; your transducer will be closed to the patient while you're zeroing so the square wave won't be possible. I always zero first and then immediately, while I'm there already, do my square wave. Saves steps. Also that way, if the atmospheric pressure HAS changed since the last zeroing, the square wave info will be more accurate. As for how often to do the square wave, I'll repeat it if there's a dampening to the waveform - the peaks aren't as sharp, I can't see the dichrotic notch any more, the patient's pressure has sagged for no obvious reason - and also if the reverse is true. Always troubleshoot your equipment before assuming that there's a problem with your patient!
    Hawkeye-RN likes this.
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    Thank you!!~
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    Great info in this post here! The previous mention of the dichrotic notch brought back some memories from a teaching session I was given hastily one day during my preceptorship regarding different "peaks" in waveforms. I can't, for the life of me, remember anything besides the mention of three different letters... (maybe, ironically, 'C', 'V', and 'P'??), and how they correlated with ..... ventilated patients insp and exp? This particular nurse had some little diddy on how to remember the letters and what they meant was happening.... Anybody have any suggestions/more info into what this could have been? (I apologize for the vagueness)....
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    So imagine I have a Pt here in Fla with an art line. When I assess this Pt, I 'zero' the line by reciting the little jargon that I first learned 25yrs ago: OFF to the patient. (I turn the stopcock towards the Pt). OPEN to air. (I take the cap off the stopcock.) ZERO the line. (I push the zero button on the monitor.) SQUARE the wave. (I pull the ponytail and make sure there is a vertical up and a vertical down on the waveform.)

    Just wanted to say thanks for this very awesome way to remember how to zero the art line. We have Alines in our Thoracic/Cardiac IMU, and I dont work there often enough to remember how to do this. Fortunately, our techs are awesome, and they give me a quick refresher beginning each shift I am back there.