CVP readings

[sazza]

Hi everone.

When reading the CVP via a monitor. First you need to zero the transducer, to set it to atmospheric pressure. On our monitors it says "offset to, lets say, 5mmHg". My question is, when you eventually record the actual CVP do you take the zeroing reading into consderation? Or is the value on the monitor the value you record?

For example:

When zeroing, the transducer is offset to 5mmHg. The monitor then records 10mmHg as the CVP. Is the CVP 10mmHg or do you use the offset value. So that the CVP is actually 5mmHg.

Also what are the lowest levels a CVP could record. I.e could it record minus levels?

I hope this all makes sense to you.

Any help here would be appreciated

Thanks

sazza

[SEOBowhntr]

John,

I've seen a couple patients who had negative CVP's, but they were EXTREMELY DRY!!! And yes, their Right Heart did literally suck the blood. I was drawing blood on one and didn't clamp the tubing and when changing syringes, watched it literally suck the blood right back in. Nothing several liters of saline didn't cure. I've also had a Post CABG one night with a CVP reading of 23mmHg and a BP of 74/34, any ideas where he shut down his graft??? Severe RV Hypokinesis, required 4 days of a 1:1 Balloon pump, and then an additional 3 days of weaning, and he ACTUALLY made it out of the hospital!!! I couldn't believe he lived!!!

[papawjohn]

Hey SEOBowhntr

I re-read my post. You're right, I didn't make it clear that the negative numbers--even if they are sort of mediated by negative intra-throacic pressures--show BIG TIME volume depletion!!!

Thanx for setting that straight. And for the mention of the R Ventricle hypokinesis in terms of HIGH CVP and LOW arterial BPs. I've mentioned that phenomenon a couple of times on these forums but never saw an extreme example as you describe.

Have you gotten a deer this year?

Papaw John

[SEOBowhntr]

Not really correcting you as much as showing an extreme case and why the CVP readings are important. I think a CVP can show you a lot about a patient, and aren't used as much and well as they could be.

OFF TOPIC:

John,

Actually, I have gotten both a buck and a doe this season, there's a picture of him here: http://www.ohiosportsman.com/photopost/showphoto.php?photo=1724&password=&sort=1&cat=540&page=4

And a picture of the perfect heart shot here: http://www.ohiosportsman.com/photopost/showphoto.php?photo=1726&password=&sort=1&cat=504&page=1

[dfk, RN, CRNA]

you would subtract the offset number.. but that's different from what we use.. we just zero at phlebostatic axis while pt is LAYING FLAT (optimal normotensive position).. take a reading and that should be the most accurate number..

[haitham abo majed]

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[ccrnjen]

Monitors do not always provide an accurate reading, particularly when there is respiratory artifact on the waveform. In order to get the most accurate reading, CVP should be read during the end-exhalation phase of breathing, when intrathoracic pressure is "zero". That is, there is not negative pressure for inhalation or positive pressure during exhalation (or vice versa on the ventilated patient).

The CVP waveform consists of three waves (A, C, V). The 2 most accepted ways to obtain a CVP reading are to take the mean of the A wave, or find the z-point. Because determining which wave is the A wave can be difficult, especially for newer nurses, and because of abnormal rhythms (a-fib, AV dissociation) and physiologic abnormalities , I think using the z-point method is easiest.

The z-point is found at the end of the QRS, just before the C wave (which represents tricuspid valve closure). It is a good indicator of right ventricular end diastolic pressure. To do this, make sure your transducer is at the phlebostatic axis and zeroed to atmospheric pressure. The head of the bed can be up to 30 degrees. Print a strip of your ECG and CVP waveforms, determine exhalation on the respiratory cycle, taking into account whether your patient is spontaneously breathing or on a vent (remember that exhalation is almost always longer than inhalation). Draw a line from the end of the QRS down to the CVP waveform and take the reading (be sure to check the scale!) - best to average a few. When this is done, you shouldn't have a negative number which is usually caused by negative intrathoracic pressure.

All this said, many clinicians simply trend CVP measurement and treat it (or end treatment) when it has changed significantly. However, if there is significant respiratory artifact, you could be over- or under- treating your patient based on a "false" reading.

Hope this helps and doesn't confuse things!

[ALCCRN]

The monitors say "offset" because that's how much the compensated when you re-zeroed. You always record the number on the monitor because the monitor takes an average of the readings. CVP can NEVER be a negative number. If it is a zero number, you need to re-level and re-zero.

[dorimar, BSN, RN]

I have to disagree about always taking the number displayed by the monitor. The moniter trends an average. You need to finde end expiration. As someone else metioned, with respiratory artifact, you can have numbers ranging from -4 to 12. The moniter number will give you an average between them and does not give you a true reading. End expiration is the true CVP. I do believe somone already mentioned that but i had to clarify the last poster.

[RYNOBLASTER30]

Occured the other day. I kept hearing this nurse say that her patients CVP was negative. You can't have negative numbers. If you do, then the set up is incorrect. Remember that normal CVP pressures are 0-8 mmHg. Funny, I took care of that same patient the day after, and come to find out they had the transducer hooked to the proximal port. Always, always, the transducer should be hooked to the distal port.

[Scoobiedoo]

I am a little confused. Why exactly is a CVP used and what info does it give you?

Thanks...

[nurserangel_65]

First things first... if your CVP is showing negative numbers... check the placement of the transducer in coorilation with the patient. Also make sure that it is in the proper port.

The measurement should be taken at the end of expiration. So if your patient is on a vent you usually measure in the valley, with spont. resp. you measure at the peaks. I have seen negative pressures with dry patients who have increased resp. effort. That is why we measure at the end of expiration.

CVP measures cetral venous pressure. This measurement is taken in the RA and indicates the fluid volume status of the pt.

[profnurse01]

You can think of zeroing a CVP as similar to zeroing a scale. Once you zero the transducer, you eliminate the atmospheric variable. The position of the patient does not matter. What does matter is that the transducer is placed level to the right atrium, or phlebostatic axis (mid-axillary, 4th ICS).