Negative CVP?

CritterLover, BSN, RN · Jan 10, 2005

many people will have a negative cvp with inspiration, esp if the cvp is running low. think about it: unless on a ventilator, breathing in is due to negative pressure created in the thoracic cavity. this is why it can be possible to suck in air and get an air embolus during the d/c of an ij or subclavian; why we put people in trendelenberg and have them do the valsalva maneuver (positive pressure) to pull a neck/chest line. does this make sense? it's been a long day.....

stbernardclub · Jan 10, 2005

It of course measures right side heart pressure. Since it measures pressure, it is directly linked to fluid volume. So a low reading (below 2) would show a volume deficit or venodialation that could be caused by sepsis,drugs,or neuro complications.

begalli · Jan 10, 2005

In addition to what has already been said very well here, what you might see with a low CVP is a labile blood pressure or consistently low blood pressure, decreased urine output, decreased cardiac output and index.

A person can have a low CVP and appear to be fluid overloaded (edematous) when, in fact, they are dry (volume depleted) because of third-spacing (a sure sign in a septic patient).

If the doc wants the patient to run on the dry side, which is often the case with cardiac patients, and the patient is not sympotmatic with the low cvp, then great!

If the patient is or becomes symptomatic, and the doc doesn't want fluid replacement, vasopressors such as dopamine, neo, etc. can be titrated to bring up blood pressure.

Usually we have parameters for cvp. If the cvp wanders above or below the parameters we'll either call the doc to see what we might like to do; or using standing orders we will either replace fluids, draw labs to check the hct if bleeding is suspected, or start drips.

Good for you for not just taking "oh well" route. Understanding hemodynamics was one of the hardest things for me to grasp. But, among other things, hemodynamics is what ICU is all about and with time, you will know and be able to explain things expertly!

RN92 · Jan 10, 2005

What Im hearing, is that with negative cvp - i should be looking for fluid volume defecit of one source or another. Thanks guys.

carebear64 · Apr 5, 2005

Im an old nurse (14yrs), but new to ICU. Hoping someone can answer a question for me. What does it mean or what can it mean when your cvp number goes negative? I know the transducer has to be level with the heart. The number was positive all day and all of a sudden goes negative. Checked the equipment, pressure bag, etc..found no mechanical reasons. Asked my preceptor. He said that if Ive checked everything, then thats all I can do. HUH?
Is there any "medical" reason why it would go negative? If not, why dont the monitors stop at zero? I cant handle just saying, "oh well,just wait and see if it fixes itself". Im the type of person that has to know why this is or is not important to know/remember.

Sometimes it is a positional thing. Repositioning the patient, and then manually flushing the cvp with a syringe (not just pulling on the pigtail) can occasionally fix this problem. Then again, sometimes nothing fixes it. If all other fluid volume issues are addressed, I would consider that there might be a problem with the catheter or maybe the tubing set up should be changed.

bluesky, BSN, RN · Apr 17, 2005

Sometimes it is a positional thing. Repositioning the patient, and then manually flushing the cvp with a syringe (not just pulling on the pigtail) can occasionally fix this problem. Then again, sometimes nothing fixes it. If all other fluid volume issues are addressed, I would consider that there might be a problem with the catheter or maybe the tubing set up should be changed.

Yup, the transducer may just be wacked. I have only been in SICU for about 8 months, but I haven't really seen a negative CVP yet. I've had a couple of negative ICPs after the pressures equilibrated, though.

If I were in your situation, first I would look for other signs and symptoms of hypovolemia. If my MAPs are OK, urine output and spec/grav OK, etc then I might change the transducers and the lines after manually flushing as previously stated. I think it is very wise and safe of you to have this concern- never ever ever doubt your instinct... no matter what anyone says.

Oh yeah... and if you have a pt in whom they are suspecting hypovolemia with a central line who doesn't have a CVP... you can always score major points by making the suggestion to a tired resident or attending who hasn't thought of it yet! :)

diddoms · Apr 17, 2005

CVP measures pressure in the Vena Cava which sits in the Thoracic Cavity. During inspiration we create a negative chest pressure in order for air to fill our lungs, and then a positive pressure to expell air.( Boyle's LAw) CVP should always be taken at END EXPIRATION. This is when the air pressure in the chest equals the air pressure outside. Since at end expiration there is no difference in air pressure what you are reading is purely the CVP. It is actually quite a skill to read a CVP accurately. Patients with any respiratory condition can have abnormally high or low chest pressures, and these thoracic pressures are all reflected in the CVP. If you want more info I'd recommend you read "Hemodynamic Monitoring" by Gloria Darovic( Saunders)

Q1 Are you reading the CVP frm the wave or just the number? Whilst the number is often accurate, it only gives an average or mean pressure.

Q2 I think you mentioned you checked the equipment,I'm assuming that included a re zero. ? In my exerience transducers often wander. If you had a faulty transducer that may have accounted for the problem. If all these things had been checked try another cable. A faulty cable will lead to loss of zero. YOu can get sucked in because you've just rezerod and the numbers are going wild. Wiggle the cable around and see if that makes a difference. After the cabl;e I'd then try a new transducer.

Hope this helps.

Regards

glascow · Apr 17, 2005

I agree with the above post. Make sure you are reading the CVP end expiration. The wave form can vary so much, esp. if pt is taking deep breaths, that if you are just reading the avg. number on the monitor, it may be wrong.

Sometimes we get to reliant on the computer generated numbers, and forget to pull up the wave form and measure it our self.

poppy07 · Oct 29, 2007

The other day I was so busy with my pt's, I tried checking a CVP, it read in the teens, and then went to -40 something. The shift prior never checked a CVP. I made a poor assumption that maybe the CVP was not such a concern at this point as the pt had been post-op for a week or so already, with stable VS, just wavering blood sugars, etc. End of shift, I realized the MD had written another order on the previous RN's shift to make sure CVPs were still being checked. I feel like this was negligent on my part.

nurseabc123 · Oct 30, 2007

What Im hearing, is that with negative cvp - i should be looking for fluid volume defecit of one source or another. Thanks guys.

Although volume deficit will often measure as a low CVP it will not cause a negative CVP, inspiration (negative pressure in the thoracic cavity), as mentioned, will cause a negative CVP reading. Just to clarify.

poppy07 · Oct 30, 2007

how do you determine the CVP yourself? Our monitor shows a crappy wave form and a number, that's it. By the way, how should the CVP waveform actually look?