Jugular Venous Pressure
Understanding the physiology and ultrasound evaluation of the JVP
This chapter comes in this place in the text book for several reasons. First, the physiology discussed is important for understanding a variety of cardiac pathologies. Second, the JVP should be evaluated early in many patients having cardiac POCUS. Third, it nicely uses the color Doppler (Color) concepts discussed in the previous carotid artery chapter.
Right atrial pressure (RAP) and central venous pressure (CVP) are measured invasively in the supine position with a pressure transducer catheter. The pressure is usually reported as a mean (normal = 2-6 mm Hg) but normal peak pressure of an a-wave is less than 10 mmHg. The RAP/CVP varies throughout the cardiac and respiratory cycles and specific variations can have diagnostic importance. Atrial fibrillation (lack of an a-wave), tricuspid regurgitation (large v-wave), and Kussmaul sign (rise in pressure with inspiration instead of a fall) would be specific examples.
The phlebostatic zero point for the heart (middle of the right atrium) was defined decades ago and lies reliably at the intersection of a horizontal line from the fourth intercostal space at the sternum with the vertical mid-axillary line. This zero point is roughly static for any position from supine to upright. In a patient who is fully upright (usually sitting), the zero point is simply at the fourth intercostal space at the sternum. As will be emphasized below, a good and fast approximation of this location is half-way between the supra-sternal notch and the caudad tip of the xiphoid process.
Jugular venous pressure (JVP) estimation was supposed to be a non-invasive surrogate for CVP. However, visual JVP has correlated poorly with CVP and many have trouble observing the neck veins, particularly in obese patients. The right internal jugular vein (IJ) is better for JVP assessment because it is in a more direct line with the right atrium.
The JVP is the vertical distance (in mm of blood column height) from the zero point to the highest level of distention in the right internal jugular vein. The peak occurs with expiration in spontaneously breathing adults, unless there is a positive Kussmaul sign.
Since other hemodynamic measurements are in mmHg, JVP is best expressed in mmHg by dividing the measured blood column height (in mm) by 13, which is the approximate density difference between mercury and whole blood. For example, a measured peak JVP of 130 mm is 10 mmHg.
JVP is a peak pressure and can never agree with a mean CVP. Normal IJ distension can only be seen above the clavicle in the sitting position of small adults. Most normal adults must be ≤ 45 degrees elevation to show distention and even then, the valve between the IJ and the subclavian vein (ScV) often blunts the distension. The lower limit of normal for peak right atrial pressure is about 6 mmHg, which is 78 mm of blood column height. Even in the fully supine position, the vertical height from the zero point at the mid-axillary line to the top of the clavicle is greater than 80 mm in most average sized adults. Thus, we can’t measure lower than normal JVP in an average sized adult. Only with very small adults might we be able to measure a JVP lower than 6 mmHg.
Careful observation of an IJ in the transverse view can identify the location in the neck where the IJ becomes mostly collapsed. Another definition of the top of the IJ distention is in the longitudinal view where the vein collapses to a “beak”. Whether looking transverse or longitudinal, be sure to use light pressure so the IJ is not artificially compressed. The following clip is a longitudinal IJ view just above the clavicle in a semi-recumbent normal patient. The beak is easily seen and the valve at the ScV is seen fluttering open and shut on the right side of the clip.
Peak JVP measures lower than peak CVP. The valve between the IJ and the ScV may be part of the underestimation, but other authors (Chest 2011;139:95-100) suggested that the cause is active venous tone that causes the IJ to collapse lower down than if the vein was only a “passive, floppy tube”. Therefore, a peak JVP is not a direct estimate of peak CVP but a separate indicator of right atrial pressure. We think the best upper limit of normal for the peak JVP is about 10 mm Hg.
METHOD AND EXAMPLES
With the patient sitting, classical technique starts with identifying the sternal angle which marks the location of the second rib. The image below shows the sternal angle marked and then the 2nd right intercostal space below the rib was marked.
Move down from the 2nd to the 4th intercostal space at the sternum and mark this location. This would be the zero point for a sitting patient.
In the picture below, the distance from the zero point to the top of the clavicle happens to be about 130 mm. If no IJ distention was visible above the clavicle, the peak JVP would have been < 10 mmHg and clearly normal.
A SIMPLE SCREEN
For routine screening, eyeballing the location on the right sternum that is half way between the suprasternal notch and the xiphoid tip is an acceptable approximation of the 4th intercostal space and is quicker than counting rib spaces. For any patient less than about 70 inches in height, the distance from this midpoint to the top of the clavicle in the sitting position is rarely over 130 mm and a mostly collapsed IJ in this position indicates a JVP < 10 mmHg. This simple screen for elevated JVP takes 5-10 seconds in the great majority of clinic patients. If the IJ is distended, the vertical height is measured.
For upright patients taller than 70 inches, the JVP may still be modestly elevated without IJ distention above the clavicle. To evaluate these taller patients, the phlebostatic zero point at the mid-axillary line is needed, along with 30-45 degree patient elevation. Have the patient put his right hand on his head. Put your right little finger on the mid-point at the sternum and stretch your thumb out horizontally toward the side of the chest and put a mark at the mid-axillary line intersection.
DETAILS OF IJ ASSESSMENT
Place the linear probe lightly and transversely on top of the right clavicle, getting it perpendicular to the vessels. Find the carotid artery, using Color if necessary. The IJ will usually be mostly collapsed, but still subtly varying, on top of and lateral to the carotid. If you are unsure, ask the patient to do a modest Valsalva. The following clip shows a sitting patient with a normal, mostly collapsed IJ with subtle variation, followed at the end by a modest Valsalva that distended the vein.
In any body position, if the IJ distention is above the clavicle, find the top of the distention and measure the vertical height from the phlebostatic zero point and convert this to mmHg. When the IJ is mostly collapsed in a taller sitting patient, lower the patient to 30-45 degrees and repeat the IJ observation using the mid-axillary line zero point. Here is a shorter, normal patient at about 30 degrees elevation showing that it is only 100 mm from the zero phlebostatic point to the top of the clavicle. That means the peak JVP is less than 100/13 = about 8 mmHg. In a taller patient at 30 degrees elevation, the top of the clavicle might be at the 130 mm (10 mmHg) level, which would be normal.
In any patient with elevated JVP, specifically watch the IJ while the patient takes moderate breaths. The JVP should fall with inspiration (there is a little time lag), unless there is a Kussmaul sign. The following clip was obtained from a patient with pericardial tamponade. Inspiration, with a dilated IJ, is at the very beginning of the clip and then the IJ collapsed as the patient exhaled.
Virtually any condition that compromises the right side of the heart and increases right atrial pressure can produce a Kussmaul sign. The sign is therefore a nice indicator of right sided disease, but not specific for an etiology.
The following clip shows a transverse view of the IJ in a normal patient at about 30 degrees. The IJ is more distended than in the upright patient, but it is still about half collapsed. There is variation with each cardiac cycle because blood is always coming down the IJ from the head and accumulating at the IJ/ScV valve. Then, when the right atrium relaxes during RV systole, the IJ empties into the ScV. Respiration also varies the distension of the IJ.
COLOR FLOW DOPPLER
Here is the same patient at 30 degrees in longitudinal view. This clip was taken at the IJ “beak” and the carotid is in view. The IJ flow was blue from the head (left side) while the carotid was showing red flow from the heart (right side).
With elevated JVP, the IJ/ScV valve may start to allow some flow through and red from below may be seen. With substantially elevated CVP, a large a-wave or v-wave may transmit up the IJ. If the carotid pulsation (with or without Color) is in view, an a-wave will occur slightly before the carotid flow and a v-wave occurs at the same time as the carotid pulsation.
With more severe TR, the IJ in the sitting position will be obviously distended and pulsating and Color is almost not needed to further evaluate. Color can show red flow coming from below. The top of the JVP is sought, but it may be up above the jaw in severe TR. Here is a transverse view, obtained in the upper neck without Color, from a patient with substantial TR.
And here is the same TR in longitudinal view showing the top where the beak appears.