Normal CVP?

[nursingdude78]

I recently had a patient who had orders to give a 250 ml NS bolus if her CVP dropped below 12. She was on a vent, and 10 mcg of levophed with systolic of 100-115. She had ascities with a lot of fluid in her abdomen. Can someone please explain the physiology behind this? I thought normal CVP was 5-10. Why would we want it above 12?

[criticalHP, MSN, RN]

Is this due to the extra PEEP when someone is intubated? Our sepsis orders have a goal of 8-12, regardless of vented/not vented. Thanks!

Sue, I've been searching a while for the answer to this--I just can't find it. It certainly seems to make sense though. Intubation and added peep increases intrathoracic pressure which results in decreased venous return and subsequently decreased CO. I'll post the link to Manny Rivers Paper on severe sepsis; I couldn't find anything there but this is the paper that began early goal directed therapy protocols that our ICU (and many others) have adopted. Many hospitals have modified this as new knowledge is discovered (which happens every couple of years it seems). If the link doesn't work I used a basic google search for "Manny Rivers sepsis paper".

Sorry I couldn't anser your question more directly. It is quite possible too, Sue, that as most hospitals will adopt a modified version of the original recommendations, the higher CVP requirements at my institution were implemented based on the infectious desease medical control policy.

http://www.nimbot.com/EGDT/Early%20Goal%20Directed%20Therapy%20in%20the%20Treatment%20of%20Severe%20Sepsis%20and%20Septic%20Shock.pdf

[rhodochrosite]

Inspiratory pressure from the vent causes a rise in CVP.....

[chani]

many oz docs refer to CVP as a random number generator and many posters have identified all the things (abdominal ascites, ventilation, PEEP) which interfere with a 'correct' reading. Additionally this patient is losing protein into the abdomen so NS replacement?? Anyway fluid replacement for liver failure is like poring fluid into a sieve. If the patient still has significant SIRS or sepsis then they require proper haemodynamic monitoring such a PICCO or [biting my tongue] PA catheter.

[reyfresco]

When a patient is mechanically ventilated this increases the inter-thoracic pressures thus giving the appearance of an elevated CVP. So if a patient has a a CVP of 15 when ventilated, it is coomparable to a CVP of 12 in the non-ventilated patient.

[meandragonbrett]

So if a patient has a a CVP of 15 when ventilated, it is coomparable to a CVP of 12 in the non-ventilated patient.

Depends on the amount of peep/PS.

[aCRNAhopeful]

Depends on the amount of peep/PS.

I agree, I don't think that the "keep CVP >12 for vented pts" is necessarily correcting a falsely elevated CVP because like meandragonbrett said, the amount false elevation depends on the amount of ps and peep. I think it's more d/t the fact that when using positive pressure ventilation in a septic patient with a low svr you are going to have profound drops in your preload every time they receive a vent breath. They need to be tanked up a bit so that the vena cava wont collapse everytime the vent blasts a bunch of pressure into the thorax.

[chani]

Dear all

on aussie forum we have also been discussing CVP. Below is a posting from a senior ICU specialist about the physiology of CVP.

CVP Measurement

This is the Achilles heel of the CVP. Like all intravascular measurements the baseline MUST be checked prior to every recording. if using the centre of the RA always use a spirit level or other manometer to a zero permanently marked on the patients lateral chest wall. Neglect of this basic prerequisite is the commonest cause of fluctuating

incorrect CVP readings.A simple alternative is to use a" centrally measured JVP". This is done by taping the transducer to the patients manubrium sterni. With the catheter in the SVC the normal reading is +/- 2mm Hg . This reading is done with the patient at 30 degrees to give a little hydrostatic stress to the circulation and to reduce the effect of raised intra-abdominal pressure. The beauty of this technique is that the baseline is a constant bony landmark and a spirit level is not necessary. Also observation of the patients JVP allows direct comparison and helps reinforce clinical skills in measuring this critical sign.

This "central"JVP is my preference

CVP Interpretation

CVP is determined by 4 factors

1. Blood volume

2. R heart function

This includes conditions such as a.Pericardial tamponade b.RV dysfunction c.Tricuspid and pulmonary valve pathology d.Pulmonary hypertension due to pulmonary embolism, lung disease, acute sepsis, many but not all cases of LV failure etc

3. Pleural pressure with IPPV, PEEP, tension pneumothorax

4. Venous tone --Be aware that with acute hypovolaemia there is acute sympathetic induced venoconstriction that takes considerable time to wear off. The CVP can be quite high during the initial stages of fluid resuscitation before it drops.All these factors must be considered when assessing the CVP. In the majority of cases it is the

relatively simple problem of adjusting blood volume.

In summary A low CVP is due to

1. Low blood volume

2. Venodilatation with peripheral vasodilatation from various causes

A high CVP is due to

1. High blood volume - overtransfusion

2. Impaired R heart function

3. Raised pleural pressure

4. Venoconstriction

Because of these varying influences one must relate both the actual level of the CVP and the relative changes that occur during the course of a patients illness. It must also be correlated with other observations such as temperature, pulse, BP, fluid administration, urine output, CXR, cardiac output and ECHO to name the key ones.

It is a shame that folks cannot think of patients in physiological terms and and utilise this simple measurement which for 50 years has been one of the key vital signs of clinical Intensive Care.

I dont take credit for the review

[Chisca, RN]

many oz docs refer to CVP as a random number generator

[MEDICJOHN]

Man, you ICU nurses make us look like blubbering idiots!!! That answer sounded like an MD! Impressive