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Calibrating CVP/ART/etc

MICU   (3,255 Views 12 Comments)
by nurs1ng nurs1ng (Member)

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The way I was taught to calibrate transducers (CVP, ART) was to put the transducer on a rolled up towel right beside the pt in a supine position as long as it's at the phlebostatic axis level.

I've seen a nurse (for the very first time) have the transducer literally be under the pt's armpit but CVP was reading at a much higher number than when it was on the towel beside the pt.

My question is, having the transducer right next to the pt's skin - would this be less or more accurate?

Thanks.

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meanmaryjean has 40 years experience as a DNP, RN and specializes in NICU, ICU, PICU, Aademia.

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Should not make a difference. Uncomfortable for the patient I suppose.

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70 Posts; 1,689 Profile Views

When you're zeroing a transducer, you are zeroing it to atmospheric pressure. The only position changes that affect it are height (up or down).

The transducer is "assuming" position where it was zeroed, so if you raise it (above the zeroed point) you're pressure will be underestimated and if you lower it, it will be overestimated. Proximity to the patient has no effect.

I would guess some put it right next to the patient to better approximate the phlebostatic axis point. I have taped them to a patient, had them on the bed, and mounted them on a pole, all for different reasons. I've also put them at the head for neuro patients and at the hip in flexed and t-burg positions.

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1,319 Posts; 12,054 Profile Views

Where the transducer is when it is zeroed makes no difference at all, as long as the atmospheric pressure where the patient is is the same as where the transducer is. You could zero with the transducer on the floor or taped to the ceiling and as long as you leveled it with the chamber that you were monitoring pressure afterward, it would be accurate.

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hotcoffee has 10 years experience.

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Is that true?

My spatial relations ability is poor but it sounds wrong to me.

i know that once you zero the transducer if you lower it you will get higher readings but I am not actually sure about zeroing it at different levels.

ive always done it in the accepted fashion-zeroed art and venous at phlebostatic axis.

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1,319 Posts; 12,054 Profile Views

Is that true?

My spatial relations ability is poor but it sounds wrong to me.

i know that once you zero the transducer if you lower it you will get higher readings but I am not actually sure about zeroing it at different levels.

ive always done it in the accepted fashion-zeroed art and venous at phlebostatic axis.

Don't take my word for it. Try it for yourself.

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hotcoffee has 10 years experience.

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Yep you're right. You can zero close to the floor and it does t matter.

weird how when you lower the transducer it reads a higher pressure.

i do t understand the physics of it.

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AnthonyD has 7 years experience and specializes in Critical Care, Med-Surg.

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Yep you're right. You can zero close to the floor and it does t matter.

weird how when you lower the transducer it reads a higher pressure.

i do t understand the physics of it.

When the transducer is being zeroed (open to air) it's reading atmospheric pressure, which is the same near the floor as it is at the bed level. When the transducer is closed, you're essentially seeing a measure of the pressure of the fluid in the tubing. So by lowering the transducer to the floor, you are measuring the added pressure exerted by the weight of the column of fluid in the tubing (from gravity). Raising it up higher has the opposite effect.

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hotcoffee has 10 years experience.

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Makes sense

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airborneinf82 has 8 years experience as a BSN and specializes in Trauma and Cardiovascular ICU.

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As long as, while reading, it is properly positioned, it doesn't matter where it is in relation to the patient. Some places place them on poles, on the side of the bed, in the bed, on the patient. Doesn't make a difference.

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hotcoffee has 10 years experience.

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Actually it does matter where it is positioned vertically when transducing but not horizontally

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VANurse2010 has 6 years experience.

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The way I was taught to calibrate transducers (CVP, ART) was to put the transducer on a rolled up towel right beside the pt in a supine position as long as it's at the phlebostatic axis level.

I've seen a nurse (for the very first time) have the transducer literally be under the pt's armpit but CVP was reading at a much higher number than when it was on the towel beside the pt.

My question is, having the transducer right next to the pt's skin - would this be less or more accurate?

Thanks.

If it makes you feel better, CVP by itself without other assessment factors is pretty much a random number. It's not even used in some ICUs depending on the disease process.

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