Quote from raindrop
First of all, what is so significant about the number? What is a normal number for someone healthy? What does that number mean??
Now, can anyone expalin to me, step-by-step, how to get a CVP reading?
Normal is (corrected again - 2-6mmHg). It is Central Venous Pressure or the pressure of the veins in the Vena Cava as they enter the heart.
You get the measurement by having a line in place along that route and transducing the pressure within the vena cava. The two most common examples of such lines are Swan-Ganz catheters or subclavian/IJ central lines.
A pressure tranducer system is connected to the Swan or to one of the central line ports (I was always taught the distal (brown) port, but our anesthesiologists always seem to hook them up to the medial (blue) port.) Once that line is connected to the patient, it is 'transduced' - the pressure is carried through a transducer to a connection on a critical care/OR monitoring system to the monitor and the monitor interprets that data.
The transducer system has to be under pressure, so it is attached and primed with fluid (we use 1000units/heparin in 500ml NS but some places just use 500ml of NS). Then a pressure bag is inflated around the fluid to 250-300mmHG pressure.
The actual transducer (a little smaller than a credit card) has to be 'leveled' to the patient. We level it at the phlebostatic axis (the midway point between between the how do I say, height and width of the chest. Think midway along the ribs between the width of the body at about the nipple line). It is usually attached to a transducer holder mounted on an IV pole that is attached to the bed.
The higher the pressure, generally speaking the greater the amount of fluid in the vein. It gives information about vascular volume. We don't want just to know how much fluid you have inside you - we can discover that by measuring I&Os. We want to know how much fluid is circulating in your vascular system.
A low CVP is probably consistent with low BP. If we know its due to low circulating volume, we can replace with fluids. Low BP with a high CVP probably involves other factors and so would first be treated with pressors.
The first rule of pressors, generally, is to replace volume first. It does little good to press down on an empty system. So CVP is important in knowing how to treat BP.
CVP is also used in the calculation of other Swan readings, such as SVR (systemic vascular resistance) and those reading provide a more direct picture of how the heart is doing, including an indirect measure of Left Ventricular End Diastolic Pressure (how the left heart - the side that pumps reoxygenated blood to the major organs - is doing). Knowing the 'hemodynamics' of the heart gives you a better idea of what kind of treatment will aid the heart instead of hinder.
Basically, our medications either beat the heart to work harder (using more oxygen) or it relaxes the heart so that it uses less oxygen (but works less). There is a tradeoff - doing one complicates the other and vice versa. Knowing what the status of the heart is to determine the best treatment is essential.
CVP is an essential measure of that. The heart is a pump. CVP gives an idea of how 'primed' the pump is. CVP is a measure of preload.
As an aside, balloon pumps do both - make the heart work more efficiently AND provide better oxygenation - that is why they are sometimes preferable to meds.