CVP and PAD

There are 2 pressure gradients in the circulatory system, a high and a low. The right side of the heart is a low pressure system, the left a high one (right side pumps into the pulmonary system, the left systemically). The left side should ALWAYS be higher than the right to pump effectively against SVR and effectively perfuse the entire system.

If the CVP is higher than the PAD, I would first check your swan because the problem is most likely in the setup or placement. If your swan placement is good, there's an adequate waveform and it's properly zeroed and transduced and your PAD is still lower than your CVP, you've got a fairly serious cardiovascular compromise going on.

Any particular reason on why you guys don't wedge?

Alright, that rationale makes a lot of sense! Thanks for the reply.

The reason we don't wedge, as a regular practice, is because the PAD closely approximates the PCWP, and there is a risk for the patient in wedging.

Any particular reason on why you guys don't wedge?

A lot of hospitals dont wedge anymore due to the risk of rupture to the pulmonary artery and subsequent mortality rates due to that. Our CVICU had it happen about 15 years ago by a nurse who was also a paramedic. Luckily she had seen it happen previously at other hospitals and immediately intubated the patient herself and got a surgeon over quickly to repair it in surgery. The patient lived, however the physicians decided at that time to use PAD instead of PCWP for left sided pressures.

Okay, lets see if I can answer your question somewhat...

CVP is the pressure from the Right ventricle (preload) excluding tricuspid valvular issues, pulmonary issues, or RV MI.

PAWP (or in your case PAD) is an indirect measurement of the Left ventricle filling pressures (preload) excluding mitral valvular, aortic valvular, or LV issues.

So, for the CVP to be higher than the PAWP then you would have to consider anything behind the PAWP as the culprit. When the PAWP is obtained the balloon is inflated and wedged against a pulm capillary. With the balloon inflated, it causes the PA catheter to block the view of the RV and it only sees left.

If you have a high CVP and a normal wedge, it is usually due to pulmonary edema, COPD, RV MI (decreased forward flow causes backup to the Right atrium hence increased RA pressures (or CVPs). Tricuspid valve issues will impact the result, pulmonary valvular issues will also. Pulmonary fibrosis and pulm embolus also.

Now, For a PAWP to be increased and not CVP, you would have to have something going on in the L side of the heart. You could mitral valvular regurg/stenosis, aortic valvular stenosis/regurg, LV MI, cardiac pulmonary edema, etc.

Certainly LV failure can ultimately cause RV faillure and both will be increased.

Hope this helps. The best thing I can tell you is remember which side that the CVP is measuring (RV filling pressures) and PAWP (LV filling pressures).

Remember, the first step in obtaining PA pressure readings is to visually assess the monitoring system.

You should first look for:

• adequate fluid in the flush bag
  
• 300 mm HG pressure in the pressure bag
  
• pressence of bubbles, kinks or blood in tubing
  
• PA tracing of good quality
  
• and perform a square wave test (flush for one second with in-line flushing device and observe the waveform. Observe 1-2 oscillations within .12 seconds and a quick return to baseline. This is done to assess the quality of the monitoring system)

Then you can level the system to the phlebostatic axis, zero and evaluate your readings.

The two factors that determine the PAS, PAD and mean pressures are the pulmonary blood volume and pulmonary vascular resistance.

Read your numbers at end expiration. The PAD is aligned with the end of the QRS complex. I hope that helps!

Other things to remember... the PAD cannot be used as an accurate measure of the pulmonary artery occlusive pressure...it is inaccurate in pts who exhibit RBBB, mitral valve disease, pulmonary hyptertension, decreased left ventricular compliance, aortic inssuficiency and pulmonic insufficiency. That's practically everyone in my CTICU. The reason for this in RBBB is because since there is a delay in R ventricular systole, the pulmonic valve stays closed longer than it should, so there is a drop in pressure in the pulmonary artery because the R ventricle didn't do systole yet...meanwhile during this delay there is runoff into the left ventricle which has completed systole and is open for filling so there is less blood in the pulmonary vasculature during R ventricular systole...and this will reflect in the PA pressure readings... also... remember your PAOP should always be lower than your PAD because of the pressure gradient and flow of blood in order for the blood to move forward... blood flows from higher pressure to lower... so think of it this way for PAOP and PAD corresponing pressures... If your PAOP is higher than your PAD something is wrong... These are always classic choices on certification exams... you can always knock a choice or two off those questions when they hit you with pressure readings because there always seems to be choices of scenarios with PAOP readings higher than PADS... if in clinical practice the PAOP is higher than the PAD you may have the catheter in the wrong lung zone (either I or II) instead of III. This can also be caused by overwedging the catheter or other physiological conditions, like PEEP. Oh... and if you are on a PEEP greater than 10, and you do wedge, you have to calculate your true wedge from your recorded wedge by changing the PEEP from cm H2O to mm Hg... by dividing the PEEP by 1.36 (to convert apples/oranges to apples/apples since 1 mm Hg=1.36 cm H2O), then dividing the mm Hg of PEEP by 2, and subtracting this number from the recorded wedge to get the true wedge. Other than that the PAD correlates with the LVedp, the PAD correlates with the PAOP, and the PAOP correlates with the LVedp. We never wedge so this doesn't help me!!! In fact, our CABG patients are de-swanned by the morning of POD#1.