I've spent the last year scanning hundreds of jugular veins and writing a book on point of care ultrasound. It has resulted in this preprint study on a novel method for estimating jugular pressure and right atrial pressure, and a book. The following is a more in-depth, technical deep dive into the internal jugular vein exam expanded from Chapters 14 and 15 of The POCUS Manifesto: Expanding the limits of the physical exam with point-of-care ultrasound.
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Of all the physical exam skills a clinician learns throughout their training, perhaps the examination of the jugular vein is the most iconic. It entails visually inspecting the lateral portion of a patient’s neck, looking for the top of the blood column in the internal jugular vein, and estimating the distance from there down to the heart. It was first described in 1930 by Sir Thomas Lewis, a famed British cardiologist equipped with a delightfully bushy mustache. Physicians as far back as Dr. Giovanni Lancisi in the early 18th century had already known that veins engorge in congestive heart failure; however, Lewis was one of the first to qualitatively assess the degree of distension.
He explained that congestive heart failure manifests itself “first in breathlessness, and continuing in its natural development to profound engagement of the venous system.” These symptoms often have an insidious onset, starting with shortness of breath with exercise and progressing ultimately to shortness of breath at rest. It is during this progression, he explained, when the signs of engorged veins first appear, which is why he felt every medical student “should make a full study of them.”
Calculating the Jugular Venous Pressure (JVP)
In a semi-upright position, the internal jugular vein is partially filled with blood and collapses above the level that blood reaches up to. It functions to drain deoxygenated blood into the right heart, via two even larger vessels: the subclavian vein and the superior vena cava. It can be thought of as a graduated cylinder for simplicity's sake, with the right atrium as its base and the jugular vein as its walls (Figure 1). The top of the blood column that fills the internal jugular vein in this simplified model is called the meniscus, which corresponds to the jugular venous pulsation since the top of the blood column is where the pulsations are most prominent. Therefore, the vertical distance from this meniscus down to the center of the right atrium is equal to the jugular venous pressure, which corresponds to the right atrial pressure.
The internal jugular vein is made up of two important segments: the obscured portion below the clavicle, and the remaining visible portion above the clavicle up to the patient’s jaw. In a healthy person with normal right atrial pressures, the meniscus does not reach the visible portion of the internal jugular vein, and therefore the vein is fully collapsed above the clavicle and cannot be seen. As the patient becomes more “congested,” Lewis explained, the veins engorge and the pressure rises, displacing this meniscus previously obscured below the clavicle upwards toward the jawline where it can be seen through the skin of the neck in the visible portion of the internal jugular vein.
This pressure could be measured directly with an invasive right heart catheterization, or indirectly by measuring the height of the blood column in the internal jugular vein. The vertical distance from the meniscus down to the sternum is recorded, estimating the height of the blood column in the visible portion of the vein. This is then added to the distance from the sternum down to the right atrium (corresponding to the obscured portion of the vein), which is classically assumed to be five centimeters. Adding those together, a jugular venous pressure over nine centimeters of water is considered abnormally high.
While this concept is well understood and accepted, it is not uncommon to see a cardiologist, a nephrologist, and a hospitalist come up with wildly different assessments of the JVP and overall fluid assessment in a given patient. Some may perceive it to be elevated and recommend diuretics, while others may not detect it at all and recommend IV fluids. How can this be?
As it turns out, this 'eyeball method' is not as accurate as we would hope, a lesson gleaned on a trip through the JVP medical literature. In 1974, internal medicine physicians at Northwestern University studied whether the method of Lewis correlated with the right atrial pressure, also known as the central venous pressure (CVP). They examined the external and internal jugular veins and compared them to the gold standard values obtained from a CVP catheter, which sits in the venous system just outside the right atrium and provides real-time pressure readings. While their measurements from the external jugular vein correlated with CVP, only half of those readings were within 2 centimeters of the actual value.
Interestingly, when trying to do the same correlation with the internal jugular vein used in the method of Lewis, they found that (my bold and italics) “the internal jugular veins were frequently difficult to visualize,” and therefore the sample was too small to analyze. To obtain a 90 percent concordance between the external jugular vein estimate and the CVP catheter, they explained, “an error of up to 4 cm had to be allowed. Moreover, large discrepancies were noted in individual cases,” concluding that the central venous pressure “cannot be reliably estimated by inspection of the jugular veins."
In another study from 1983 published in the New England Journal of Medicine, clinicians tried to estimate right atrial pressure in 56 critically ill patients, comparing their results to the gold standard right heart catheterization measurements. While there was a modest correlation between the JVP estimation and the right atrial pressure, the results were “better than random; however, the percentage of accurate predictions was quite low,” at about 42%. A clinical exam of critically ill patients they noted, “does not provide enough information to assess hemodynamic status accurately.” Similar results were seen in two other studies of ICU patients (here and here), as well as in a study of medical residents assessing the jugular vein from 2007. They were only able to visualize the meniscus in 37% of patients who had it in the visible portion of the vein and were particularly poor at correctly detecting elevated pressures, with only 14% sensitivity.
Such results are analogous to those published in Chest from a group of intensive care physicians who underwent a JVP assessment teaching session prior to the start of another study. Despite this added educational piece, the clinical JVP assessment for determining high right atrial pressure was limited, with a sensitivity of 43% and a specificity of 67%. Even with experienced cardiologists, the sensitivity and specificity of an elevated JVP exam to predict high right atrial pressure was 65% and 85% respectively when compared to pressures measured with a right heart catheterization. These limitations to the visual assessment of jugular venous pressure were summarized in a review article out of the University of Washington, arguing that most studies of JVP exams were inaccurate and unreliable, concluding that not much progress has been made since Sir Thomas Lewis first took a shot at it in the early 1930s.
Limitations to the method of Lewis
Dr. Lewis's brilliant technique provides a very rough estimate of right atrial pressure. However, there are two very important limitations that render this method futile in a large percentage of patients:
The meniscus or jugular venous pulsation that cannot be seen cannot be evaluated
The JVP measurement relying on the assumption that the right atrium sits 5 centimeters below the sternum will invariably fail
JVP Not Appreciated
As we routinely hear during physical exam presentations, "JVP not appreciated" is used to relay the fact that the neck was assessed and there were no pulsations present, insinuating that the jugular venous pressure is normal. Yet this is not necessarily true. If the jugular venous pulsations are not visualized, then one of four things are possible:
It is present and visible but the clinician did not detect it
The pressure is low enough in the jugular vein that the meniscus is below the clavicle and cannot be seen
The pressure is so high that the meniscus resides above the jawline and the pulsations are not present in the neck
The patient’s anatomy does not allow for it to be visualized.
So with our current methods of assessment, not seeing the jugular venous pulsation in the neck could suggest normal or low pressures, as well as extremely high pressures.
Not a very useful discriminator.
Complicating the JVP assessment further may be a patient’s thick neck or a large beard, or the fact that - in the United States at least - over 70% of patients are overweight or obese. In these patients, the meniscus may literally be invisible and therefore the method of Lewis simply cannot be used (more on this later).
Right Atrial Depth Assumptions Lead to Failure
Sir Thomas Lewis’s method has stood the test of time for getting us in the ballpark of the actual pressure. However, as we have discussed, researchers have consistently come up short when attempting to quantify it with an actual pressure value. These failures are due in part to the assumption that the distance from the sternum down to the right atrium (here on referred to as right atrial depth), corresponding to the obscured portion of the vein, is 5 centimeters when in fact it usually is not.
This chosen distance originated from a 1946 study in which they snaked a urinary catheter with a pressure sensor on it up through the arm veins and into the right atrium to measure the right atrial pressures in real-time. They wanted to choose a reference point that passes “somewhere through the heart itself and at the same time bear a reasonably constant relationship to an external landmark,” such as the top of the sternum. With the patient lying flat on their back, the right atrial depth was measured from a chest X-ray to be around 5.8 cm, yet for “the sake of simplicity ... it has been decided to take the conventional venous pressure reference level of 5 cm” below the sternum.
However, a more recent study of thoracic CT scans of 196 patients underoing a right heart catheterization tells a different story. Their data suggests the actual right atrial depth is nearly double that, at 9 centimeters, and that using the standard 5-centimeter assumption incorrectly estimates the right atrial depth 71% of the time.
This reference level turns out to be extremely important since the whole point of the JVP exam is to estimate the pressure in the right atrium, not from some point in the chest above or below it. Using the 5-centimeter assumption will underestimate right atrial pressures in the majority of patients. As depicted in Table 1, the 5-centimeter depth corresponded to the right atrium only 29% of the time.
This choice of zero reference level (ZRL) can have dramatic effects on resulting pressures obtained from the right heart catheterization (Table 2). As the authors explained, when shifting the ZRL from "the mid-atrial ZRL to ‘5 cm below anterior thorax surface’, the percentage of patients in our patient cohort with mean [pulmonary artery pressure] of 25 mmHg would decrease from 68% to 59%, while shifting the ZRL to the level ‘10 cm above table level’ would increase this percentage to 80%. Similar changes may be observed regarding [pulmonary capillary wedge pressure]," which are of special relevance "for the diagnosis of pulmonary arterial hypertension because readings greater than 15 mmHg preclude this diagnosis."
This right atrial depth also varies significantly based on the patient’s position and body size. As the head of the bed is raised and the angle increases from zero, another study using CT scans found that the median distance is about 8.8 centimeters at 30 degrees and 9.9 centimeters at 45 degrees, with enormous variation from 5 to 15 centimeters depending on the patient’s age, body size, and smoking status (Figure 3).
While the median is useful in the aggregate, in each patient the degree of variation is so large that an assumption may be off by as much at 10 centimeters of water. Therefore, for any method to be successful, it must measure this distance in each patient, an impractical feat without the use of ultrasound.
JVP Always appreciated with POCUS
The two major limitations to the method of Lewis discussed thus far can be elegantly overcome with point-of-care ultrasound (POCUS). In the POCUS Era of bedside diagnostics, the jugular vein is always appreciated, since it sits so close to the skin and is easily identified regardless of the patient’s neck size or BMI.
It can be viewed longitudinally, with the probe parallel to the vein in the head-to-toe axis of the body. As seen below, the meniscus takes on a triangular appearance that we call The Wine Bottle Sign, due to the fact that it looks (sort of) like the top of a wine bottle. Sitting just below it is the carotid artery:
You can also view the internal jugular vein in the transverse view, with the probe sitting perpendicular to the vein in the left-to-right axis. In this view, the internal jugular vein is at the 10 o'clock position and fully collapses with each breath:
While POCUS can overcome the visibility limitations of the method of Lewis, what really matters is if it can accurately estimate right atrial pressures. In the example above, the internal jugular vein will be collapsed above this wine bottle sign, while below it will be a rounded vein filled with blood. In an abnormally dilated vein (i.e. with jugular venous distention or JVD) minimal or absent pulsations will be present.
Valsalva and JVD
When a patient is sitting upright at 90 degrees, the vein is partially filled, though usually not enough to displace the meniscus into the visible portion of the vein, unless the right atrial pressure is very high. As the angle of the bed reduces and the patient moves toward being supine, the blood will spread towards the head and fill the vein, just as a partially filled bottle of cabernet when placed on its side.
When the patient reaches zero degrees and is lying flat on their back, the meniscus is no longer present and the vein has reached its maximally engorged state, the extent to which varies by the amount of blood present. In a patient with severe heart failure who has a large amount of excess fluid accumulation, the jugular vein diameter will be very large, while in a healthy patient, it will only partially engorge. The maximum diameter a jugular vein can mount may be determined by asking the patient to bear down as if they are having a bowel movement, called the Valsalva maneuver. This forced expiration compresses the heart and blood vessels inside the thorax, displacing the blood into the jugular vein, causing it to dilate 20-30% in patients with normal right atrial pressure. Therefore, in a patient with jugular venous distention and elevated right atrial pressure, performing the Valsalva maneuver should cause a smaller increase in the diameter since it is already abnormally distended at rest.
Cardiologists at the Pittsburgh School of Medicine used this physiological fact to categorize the jugular venous pressure as high (greater than or equal to 12 mmHg) or low if 11mmHg or less (Figure 4). They found that if the increase in the cross-sectional area of the internal jugular vein was less than 17%, this predicted an elevated right atrial pressure with 90% sensitivity and 74% specificity, while if it increased more than 17%, it “all but rules out high right atrial pressure ... with a 94% negative predictive value.”
This finding alone is extremely useful when examining a patient at the bedside. However, it relies on measuring the cross-sectional area which has a lot of room for error. It also involves asking the patient to perform a Valsalva maneuver, which is surprisingly difficult to explain to someone who has never heard of it. Especially if they are not English speaking (in my experience at least).
Other researchers have attempted what I call the sonographic method of Lewis, using ultrasound to identify the meniscus and measure down to the sternum in the visual portion of the jugular vein, while still relying on the 5-centimeter assumption for right atrial depth. The wine bottle sign was successfully detected with ultrasound in all jugular veins visualized, even when the standard exam was unsuccessful. However, both studies (here and here) found that the JVP underestimated the actual right atrial pressure, findings that may be explained simply by the fact that the average right atrial depth is actually nine centimeters, not five.
Right Atrial Depth: the Holy Grail
Ultimately the limitations to our physical exam and visual inspection of the jugular veins result in the need for a right heart cath. A procedure that involves sedation and has its own set of rare but serious complications. Therefore, in an ideal world, we should be able to accurately measure the right atrial pressure (and the other pressures a right heart cath provides) with ultrasound alone. For any sonographic measurement to be able to adequately replace the need for a right heart cath in certain patients, it would need to:
Precisely identify the meniscus and measure the distance from it down to the sternum
Precisely identify the center of the right atrium and measure the right atrial depth
As we have already seen, identifying the meniscus and visualizing the jugular vein above the clavicle is very simple with POCUS. Measuring the right atrial depth is possible as well. Physicians in the department of ultrasound diagnostics at the Tangdu Hospital in Shaanxi, China used the built-in measuring capabilities of ultrasound to show that they could “locate the center of the [right atrium] precisely based on solid geometry” and approximate right atrial depth with a high degree of accuracy. It involved a cumbersome but clever technique involving multiple people, an ultrasound probe, a pencil, and a ruler (Figure 5). The results were then added to the distance from the sternum to the height of the meniscus to come up with an estimated right atrial pressure. When compared to a central venous catheter measurement, they were astoundingly accurate, only off by 0.2 centimeters on average. Though still not practical for a routine physical exam, this method clearly shows how precise ultrasound can be for estimating right atrial pressures.
Simplified Method for measuring Right Atrial Depth
I've completed a 51 person study validating this method against right heart caths that resulted in this study still in preprint. Based on the results, we have a follow-up study underway to control for the confounding variables we will discuss below.
Since most patients are in the supine position during the physical exam, I wanted to use a landmark easily seen in the parasternal long-axis view of the heart. The right atrium is not visible in this view, however, the non-coronary cusp of the aortic valve is. The point where the non-coronary cusp attaches to the left ventricular outflow tract (LVOT) is in the same coronal plane as the right atrium and can be used as a surrogate (Figure 6).
Step 1: Measure Right Atrial Depth
You can find the noncoronary cusp where it attaches to the LVOT and measure to this point to estimate the right atrial depth (Figure 7). In our study, the average right atrial depth was about 10 cm, which is similar to the two studies described earlier based on CT scan measurements.
Step 2: Determine if JVD is present at the supraclavicular point
Once the right atrial depth is measured in the 45-degree position, the probe is placed on the supraclavicular point, with the probe rested gently just above the right clavicle. If JVD is present, the internal jugular vein will be dilated with minimal or completely absent pulsations:
In this example, with the head of the bed at 45 degrees, the IJV is very dilated. There are still minimal pulsations but the internal jugular vein does not collapse with inspiration. Let's see another example:
Here again, the internal jugular vein ( at 10 o'clock) is distended and there are very minimal pulsations present with no collapse with inspiration. Both of these examples qualify as JVD present at the supraclavicular point.
In this case, the probe is slid up towards the head to look for the collapse point. If this point is visualized, it can be confirmed in the longitudinal view looking for the Wine Bottle Sign. The distance from this point is measured down to the sternum. This will give you the height of the blood column in the visible portion of the vein. This is then added to the right atrial depth to get the right atrial pressure in cm of H2O (Figure 8).
If JVD is NOT present at the supraclavicular point
If the internal jugular vein is pulsating and completely collapsing with inspiration at the supraclavicular point, then JVD is not present. This suggests that the meniscus is located somewhere below the clavicle in the obscured portion of the vein. In this case, with the probe stationed at the supraclavicular point, the next step is to lower the head of the bed to 30 degrees and watch for vein engorgement. If there is no vein engorgement, then the head of the bed is again lowered to zero degrees. In this ca,se the right atrial pressure is estimated as follows:
Engorgement at 30 degrees: RAP = right atrial depth x 0.75
Engorgement at zero degrees: RAP = right atrial depth x 0.5
No engorgement at zero degrees: RAP = right atrial depth x 0.25
With this simple strategy, the right atrial pressure can be estimated within a few millimeters in the vast majority of patients. Let's see two cases:
Case 1: 75 yo F with amyloidosis
Step 1: Measure the right atrial depth
The noncoronary cusp attaches to the posterior wall of the LVOT at about 8cm deep.
Step 2: Check for JVD at the supraclavicular point at 45 degrees
At 45 degrees, the internal jugular vein is dilated with absent pulsations. JVD is present here.
Step 3: Find Wine Bottle Sign
The probe is slid up towards the head and 4 cm above the sternum the IJ completely collapses:
The probe is then turned longitudinally to confirm the Wine Bottle sign:
Step 4: Calculate right atrial pressure
In this patient, the wine bottle sign was 4 centimeters above the sternum and the right atrial depth was 8cm. Therefore the right atrial pressure is estimated at 12 cm of H2O (8 cm + 4 cm). This must then be converted to mmHg by multiplying by 0.735 to get:
Estimated RAP in mmHg: 8.82
Actual RAP from right heart cath: 10 mmHg
Case 2: 63 yo obese male
Step 1: Estimate right atrial depth
Here estimated at about 8.5-9 centimeters deep
Step 2: Check for JVD at the supraclavicular point with the bed at 45 degrees
Here the internal jugular vein (at 10 o'clock) takes on a more ellipsoid shape and completely collapses with inspiration. Therefore, no JVD is present. The head of the bed is lowered to 30 degrees:
At 30 degrees the jugular vein looks essentially the same as at 45 degrees. Still not engorged and completely collapses. The bed is lowered to zero degrees:
The vein is still collapsing but has engorged somewhat compared to 30 degrees. Therefore there right atrial pressure estimate, in this case, would be right atrial depth of 9 cm x 0.5 = 4.5 cm. Converted to mmHg we estimate the pressure to be 3.3 mmhg
RAP estimate = 3.3mmHg
RAP from right heart cath = 5 mmHg
Concluding Thoughts
This study has been submitted for publication but has yet to be peer reviewed. Overall I found that this method can very accurately estimate right atrial pressure within a couple of millimeters of mercury almost every time. A major limitation of our initial study was the fact that we compared our estimate to a right atrial pressure measured by many different cardiologists with no standard zero-level amongst them. This made it very difficult - or impossible - to say exactly how close our measurements actually were to the actual right atrial pressure. This technique measures the right atrial depth in every patient, which can vary from 5cm to 15cm. Therefore it is not clear if using a right heart cath - which uses a standard measurement on every patient - is even a good comparison to use. We have controlled for these issues and are currently underway with a follow-up study.
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Dr. Larry Istrail is a physician certified in point-of-care ultrasound by SHM and Chest. You can read the study preprint here.
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