The normal central venous pressure is 7 cm of water or less. Now, how do you estimate that central venous pressure in a patient? Well, we're fortunate. There's a marker on the chest wall, and that marker is called the sternal angle. It happens to be 5 cm higher than the arbitrary zero mid-right atrium reference point. One then compares the venous contour in the neck to the sternal angle. In this case, when we identify that venous contour in the neck on the inferolateral aspect of the sternocleidomastoid, we note that it is approximately 1 cm lower than that sternal angle. Hence, since the sternal angle is 5 and since this is 1 cm lower, in this patient, the estimate of central venous pressure is 4 cm of water. This is a really simple thing to do at the bedside.
Assessment & our patient's CVP
To repeat, the mean central venous pressure is determined by measuring the vertical height of the venous pulsations above the mid right atrium, as the latter is the zero reference pressure. The patient should be examined in the semi-recumbent position at whatever angle the veins are best visualized.
The sternal angle is used as a bedside reference point. It is 5 centimeters above the mid right atrium, and this relationship does not change significantly from the supine to the sitting position.
Neck veins normally do not pulsate to a level exceeding 2 centimeters above the sternal angle, that is, the normal mean central venous pressure is less than 7 centimeters.
The most common cause of an elevated mean central venous pressure is an elevated right ventricular diastolic pressure, such as occurs with right ventricular failure.
The central venous pressure in our patient is estimated to be 4 centimeters of water, since the sternal angle is 5 centimeters above the mid right atrium and since our patient’s neck veins undulate 1 centimeter below the sternal angle, his estimated central venous pressure is 4 centimeters of water.
"Hand Trick"
You know, I'd like to tell you a little trick I learned years ago that has helped me measure central venous pressure quite accurately at the bedside. All of us carry around a measuring device with us, that is, our own hand. Now, mine happens to be 8 cm across. So, I can go to the bedside and, using my hand, very accurately assess the central venous pressure. Incidentally, you know, that same measuring device is great for measuring the breadth of the liver.