square wave test

Mags4711, RN · Jun 12, 2006

Absolutely, I always squarewave test.

It yanks my crank to no end when the docs then come by and like the number from the cuff better so they say to use that. WHAAAA???? My squarewave tells me that my a-line is accurate, so that is truly my patient's blood pressure! I get so annoyed when the docs say, "Run a cuff pressure." Half the time I tell them if they want one, they can run it.

monkeyman1000 · Jun 12, 2006

I get that a lot too. It's really annoying when I've already explained to the family about art lines being the most accurate way of measuring the BP then the doc tells me to go by the cuff.

TennRN2004 · Jun 12, 2006

Does anybody do this? I usually try it on my art lines and CVP but when I get a wierd result, either no one knows what I'm talking about or they say ignore it. For instance, the last 2 days one of my patients had an art line and a CVP. I checked both and on the art line I had a good square wave test but the CVP (it always seems to be the CVP) showed that it was underdamped. I removed an extra piece of tubing (little short piece with a stopcock) and it didn't improve anything. The AACN guide said to add a dampening device but I and everyone else had never heard of such a thing. The actual CVP wave form looked good and the doc's never seemed to care so should I just toss this practice. Serves me right for reading.

Yep, we call the dampening device a Rose in my unit. It can be especially helpful if you are seeing a big difference between your cuff and your aline of 30-40 points, it will usually bring them closer to correlating. If your docs are not gonna treat your aline, then just tell them you'll d/c the aline. There's no point in having hemodynamic data available if you're not gonna use it. As far as a dampened CVP waveform, this can be a simple fix. I don't use a rose on it, sometimes, it is just positioning. If the line is sitting up against the vessel wall, you can try a power flush-use a 10cc syringe and flush and see if you can move it, also try having the patient cough or roll sometimes helps, sometimes not. It's hard to make the docs understand sometimes the lines are only 100% accurate when you've got a patient laying completely still at all times. If you've got a fidgeter or a schoocher that slides down in the bed or a flopper than turns side to side, your numbers can be crazy because you can't keep the darn lines level.

Zee_RN, BSN, RN · Jun 13, 2006

I always do a square wave test too. It's policy. HOWEVER -- it means nothing regarding our actual practice. We do not HAVE dampening devices. And at least 50% of my fellow nurses say "Huh?!" when I mention the square wave test. So I do it, I document it, and I try to find a reason for an over- or underdampened line but there's little I can do about it.

ICUMish · Jun 13, 2006

I also try to do the test every time I get an a-line. Unfortunately, our hospital does not have a clear policy about this. So I realized that the treatment of our patients is based on the unreliable measures (ABP, CVP, etc)

SorenDrake · Jun 13, 2006

I always perform the test first thing when I'm zeroing the lines. We don't have sampening devices, but typically if I haven't gotten a good result it's due to the pt moving, like Tenn said. Or if it's just an art line and not an art/PA/CVP line and the original nurse just slapped the transducer to the pt's arm instead of a pole next to the bed, that usually makes it not as accurate. Also, anytime we've done a bunch of movement and then get the pt settled, I try to give each a good extra flush.

papawjohn · Jun 14, 2006

Hey Yall

I do the 'square wave' test too. But to tell the truth, I think it is an anachronism. Many years ago (several decades ago, really) we had to assemble the tubing and transducer sets from kits that were autoclaved and reused. There was the usual yards of tubing and a little plastic dome that had to be filled with saline and thoroughly flushed to get the air out. And sometimes it was NOT easy. The 'dampening' of a non-square wave was from the occaisional bubble that got into the system. Since air expands and contracts under pressure (and fluids like Saline don't) a sloped wave meant that the wave and pressures were untrustworthy.

With the setups we us now--it's almost never an issue.

And to tell you the truth, it makes no sense to me to shorten the tubing. If a 'dampened' wave was fixed by removing a section of the tubing, I bet the problem was the connections being loose enough to bleed pressure--not the length of tubing.

Papaw John

Zee_RN, BSN, RN · Jun 15, 2006

Thanks for that insight, Papawjohn. I did not realize all of that. I will add that to my "lesson plan" for new nurses!

SanFranSRNA · Jun 19, 2006

I usually perform squarewave test with each of my assessment to ensure proper reading. Overdamping or underdamping would yield inaccurate measurement of BP. Overdamping would under estimate BP and underdamping would over estimate BP. From my experience, with each "perfect" squarewave test and I can pretty much guess that the cuff pressure would be slightly lower then A-line pressure.

wonderbee, BSN, RN · Jun 19, 2006

We reposition, relevel and zero the transducer or reposition the pt if over or underdamped. I wasn't aware of any device that does this. Are we in the dark ages in my unit?

SanFranSRNA · Jun 19, 2006

RNKittyKat

Squarewave test is when you flush the line and observe the wave form on the monitor. It should be perfect square with 1-2 oscilation.

A square wave test checks the dynamic response of the entire catheter monitoring kit transducer system. It is extremely important to obtain a high quality square wave test in order to assure confidence that subsequent pressure measurements are relatively distortion free and accurate