Internal Jugular Vein, Inferior Vena Cava, and VExUS
Understanding the physiology and ultrasound evaluation of the IJV and IVC
Internal Jugular Vein (IJV): We assess the IJV in sitting patients when elevated right atrial pressure (RAP) is a clinical concern. The assessment is of little use when the concern is low RAP/volume responsiveness and we do not evaluate the IJV as part of a screening IMBUS heart exam.
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 sitting fully upright, 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): JVP estimation was supposed to be a non-invasive surrogate for CVP. However, visual JVP values have not agreed well with CVP and many have trouble observing the neck veins, particularly in obese patients. The right IJV is better for JVP assessment because it is in a more direct line with the right atrium. The approach described below was shown to be “feasible, reproducible, and accurate” for predicting elevated central venous pressure in patients undergoing right heart catheterization (Wang, et al. Ann Intern Med 2022; 175:344-351).
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 IJV. 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 IJV 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 IJV in the transverse view can identify the location in the neck where the IJV becomes mostly collapsed. Another definition of the top of the IJV 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 IJV 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 is lower than peak CVP. The valve between the IJV 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 IJV 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 measure of right atrial pressure. We think the best upper limit of normal for the peak JVP is about 10 mm Hg.
For routine screening of a sitting patient, eyeballing the location on the right sternum that is halfway between the suprasternal notch and the xiphoid tip is an acceptable approximation of the zero point. For any patient less than about 70 inches in height, the distance from zero to the top of the clavicle in the sitting position is rarely over 130 mm and a mostly collapsed IJV in this position indicates a JVP < 10 mmHg. If the IJ is distended, actual vertical height can be measured.
For upright patients taller than 70 inches, the JVP may still be modestly elevated without IJV 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 mark the junction with the mid-axillary line.
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 IJV will usually be mostly collapsed, but still subtly varying, on top of and lateral to the carotid. Blood is always flowing down the IJV and accumulating at the valve. The right atrium pulls in blood during right atrial diastole, which is at the time of ventricular systole. Traditional JVP experts said, “Watch for systolic collapse of the IJV.” Inspiration also increases flow from the IJV into the subclavian vein. If you are unsure whether you are seeing the IJV, ask the patient to do a modest Valsalva. The following clip shows a sitting patient with a normal, mostly collapsed IJV with subtle variation, followed at the end by a modest Valsalva that distended the vein.
Kussmaul sign: In any patient with elevated JVP, specifically watch the IJV 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 IJV, is at the very beginning of the clip and then the IJV 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.
Color Doppler: Here is a patient at 30 degrees in longitudinal view. This clip was taken at the IJ “beak” and the carotid is in view. The IJV flow was blue from the head (left side) while the carotid was showing red flow from the heart (right side).
Tricuspid regurgitation: With elevated JVP, the IJV/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 IJV. 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 IJV 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.
INFERIOR VENA CAVA (IVC): We assess the IVC when low RAP/volume responsiveness is a clinical concern. Assessment is less useful for suspected high RAP, although a rounded (plethoric) IVC is expected with this condition.
The IVC usually fluctuates in size with RAP, but the absolute IVC lumen diameter is unreliable because of inter-patient variability; normal people can have good-sized IVCs. Of greater value is the variability of the IVC with respiration. Negative intrathoracic pressure during inspiration normally causes a transient decrease in the diameter of the IVC lumen close to the heart if the RA can accept more blood.
First assess the IVC with a short axis view 3-4 centimeters caudal of the RA. If the IVC is flattened and collapsing with inspiration the patient should be volume responsive, does not have elevated RAP, and may have reduced RAP. No further measurement is needed.
If the IVC is less flat without obvious inspiratory collapse, more precise measurement of the variability can be useful. The long axis view has traditionally been used because the lumen may be clearer. However, before moving to the long axis, notice in the short axis whether the IVC visually moves laterally with respiration, because such movement can produce artifacts with the long axis assessment.
A 2020 study of sick adult patients (Caplan et. al., Ann. Intensive Care 10, 168) showed that a location 4 cm caudal to the right atrium was the best location for evaluating respiratory variation. All patients were examined with a phased array probe/heart preset in the semi-recumbent position (30-45 degrees elevation). The study used a GE-developed application (Auto-IVC) to measure the variation and this app is now on Venue. A good view of the IVC showing the anterior and posterior walls of the IVC throughout a respiratory cycle is needed for the app to function. Poor images will not be accepted and an unsteady probe or lateral movement of the IVC during the respiratory cycle can produce false positive variability.
When Auto-IVC is activated, an anatomic M-mode cursor is placed perpendicular through the IVC and continuous measurement begins of the maximal and minimal diameters of the IVC throughout 4 second cycles. If necessary, move the cursor to about 4 cm caudal of the RA. GE chose the Collapsibility Index (CI) to express the respiratory variability and it is calculated as follows:
(1 – Dmin/Dmax) x 100
The following is the output from the Auto-IVC application in a patient with a CI of 10%.
The higher the CI the more likely a patient is volume responsive. In the study a CI of > 33% in spontaneously breathing patients had a sensitivity of 66% and a specificity of 92% for volume responsiveness. When patients performed a moderate intensity 3-4 second inhalation (not called a sniff), a CI of > 44% had a sensitivity of 93% and a specificity of 98% for volume responsiveness.
The IVC CI has not been compared with the dynamic carotid flow time for assessing volume responsiveness. If good views of the IVC can be efficiently obtained in the semi-recumbent position, the Auto-IVC measurement is faster and doesn’t require a helper to lift the patient’s legs. If the dynamic carotid flow time and the IVC CI both indicate (or do not indicate) volume responsiveness, the evidence is stronger than having only one of the assessments.
If a patient’s heart ultrasound leaves open the possibility of elevated RAP and the JVP is equivocal (or cannot be estimated), the IVC is not reliable enough to resolve the issue.
An additional tool for evaluating such patients is looking at the PW Doppler flow patterns of veins caudad of the intrahepatic IVC. Proponents are calling this a “venous excess by ultrasound” exam or VExUS. The data about this exam is early, but it seems to improve the accuracy of RAP evaluation. Almost all information has been from hospitalized patients who demonstrate that more severe VExUS patterns correlate with acute kidney injury (Rola, et al. Ultrasound J 13, 32 (2021). https://doi.org/10.1186/s13089-021-00232-8)
The veins that have been proposed for examination are the hepatic, portal, and intrarenal. The hepatic veins are complicated to interpret, and the intrarenal veins can be difficult to image. In contrast, portal vein imaging is routine for IMBUS, and the interpretation of the PW pattern is straight forward. Details about obtaining and interpreting the portal vein tracing are found in the Liver Region chapter.