On May 10th, 1930, Sir Thomas Lewis, a cardiologist at University College Hospital in London, published Early Signs of Cardiac Failure of the Congestive Type, in which he first described the methods for detecting the jugular venous pulsation (JVP):
"The commonest large pulsation in the neck comes from the internal jugular. It frequently extends to and moves the lobe of the ear, and is usually mistaken for carotid pulsation, a serious mistake to make."
This brilliant method relies on the behavior of fluids in a cylinder, and has remained the bedrock of our volume exam nearly 100 years later.
The internal jugular vein empties into the right atrium via a short portion of the subclavian & superior vena cava, and is (sometimes) visible through the skin, making it theoretically a perfect vein to assess a patient's volume status. It is also reported to have an 'incompetent valve' in most patients, however that does not seem to be the case. The valve sits just above the subclavian vein-internal jugular vein union and in a study done on live subjects and cadavers, 93% of patients had them and all were competent valves in the live subjects. The degree to which this valve affects JVP measurement has not been well described.
As fluid builds up in the venous system, as in a patient with congestive heart failure, the column of blood from the right atrium up to the visible portion of the jugular vein will engorge with blood and the top of the blood column (the meniscus) will be visible closer and closer to the patient's earlobe. Measuring the vertical distance from the top of the sternum to the meniscus (and adding 5cm to account for the distance from the sternum to the right atrium) will give you the jugular venous pressure. A JVP over 9cm of water (or 3-4cm above the sternum) is considered abnormal.
Now just how precise is the JVP? And can ultrasound do better?
A New England Journal of Medicine study from 1983 only predicted pulmonary capillary wedge pressure (PCWP) range correctly using JVP exam about 40% of the time. In 103 critically ill patients, a study from 1984 showed that physical exam could predict elevated PCWP pressure only 30% of the time and elevated right atrial pressure only 50% of the time. Another study in critical care found similar findings, noting "considerable disagreement and inaccuracy exists in the clinical assessment of central venous pressure in critically ill patients."
In a study of medical residents from 2007, JVP was not detected in 37% of patients despite being high in some of them. Overall, using JVP to estimate elevated RA pressures proven by right heart cath (RHC) had an accuracy of 60% and specificity of 78%.
In 2008, the ESCAPE trial did show good correlation between the totality of H&P findings (history, rales, elevated jvp, lower extremity edema) and right atrial pressure.
However this was in patients with known heart failure, with EF <30%. and at least one symptom and 1 sign of congestion present. They showed estimated JVP > 16 did correlate with elevated PCWP (greater or equal to 22) 82% of the time, while a JVP < 8 did not rule it out out. 18 patients had a JVP < 8 and a RHC showing volume overload. Individually, our classic physical exam findings were not sensitive or specific:
A review article from 1998 argued that the JVP exam was largely inaccurate, estimating RAP only half the time and generally underestimating pressures, ultimately concluding that not much progress has been made with the physical exam since Sir Thomas Lewis first took a shot at it:
"Further research must identify a value of venous pressure that is clinically useful in these patients, but in the meantime, Lewis’ assertion that a measurement >3 cm H2O above the sternal angle is abnormal, whatever the patient’s position between supine and upright, seems to be a good starting point that would tend to only underestimate the measured supine value."
Jugular Venous Ultrasound
Using ultrasound to evaluate JVP is a relatively novel concept with minimal amount of literature describing it. Researchers from Iowa examined JVP using ultrasound, looking for the point at which the jugular vein tapers off, corresponding with the JVP one can detect visually.
They compared this ultrasound method to physical examination and CVP using an indwelling catheter. Physical exam of JVP was only "confidently measured in 26 of 38 patients" while ultrasound exam was successful in all subjects. In patients that got both, they correlated well. When compared to central venous pressure, both ultrasound and external exam underestimated CVP, by about 5cm of H2O. The authors noted that this difference led them to "question th[e] fundamental assumption that jugular veins are passive. An alternative hypothesis is that the jugular venous walls are capable of exerting tone, presumably through contraction of smooth muscle in their walls."
This discrepancy has been reported in other studies as well and could explain why their JVP measures consistently underestimated CVP. For example if the pressure inside the IJ keeping it distended is 5cm H2O of venous blood, the vein will collapse where the external compressive force is greater than 5.
If the vein itself has contractile properties of 2cm H2O compressing the vein, this would lower the external force needed to be generated to collapse the vein to 3cm H2O, therefore lowering where the meniscus would appear in the neck.
Another technique published in 1999 involves imaging the neck vessels in the transverse plane. In this view, the internal jugular vein will be seen, usually laterally, to the common carotid artery.
Normal CVP (0-10 cm H2O) in semi-upright position
The jugular vein pressure falls as the patient goes from supine to seated. At some point in the neck, "the extravascular tissue pressure is greater than the local venous pressure and the vessel collapses." In the transverse plane, the internal jugular vein will be almost collapsed and crescent or slit shaped.
If the patient is sitting at 45 degrees and the the IJ is collapsed, then the bed must be lowered until the IJ becomes engorged with blood. Then the most superior tapering point should be marked, and the vertical distance to the angle of Louis (plus 5 cm H20) is the estimated CVP.
If the CVP is closer to zero, the vein will appear collapsed, even while in the supine position.
Elevated CVP ( Greater than 10 cm H2O)
The IJ is distended, even in the semi-upright position. In the transverse plane, it will be oval or round shaped, as large or larger than the common carotid artery.
Building on this basic technique, researchers tried to detect right atrial pressure using internal jugular vein (IJV) bedside ultrasound in 67 patients. In patients with normal right atrial pressures, the Valsalva maneuver is associated with a 20-30% increase in jugular vein cross sectional area. They hypothesized that if the patient was already volume overloaded and the IJV was already distended to some degree, that the relatively small change in IJV diameter from rest to valsalva could accurately predict right atrial pressures.
Within 1 hour of a RHC, the right IJV was measured in the supine position at end inspiration, end expiration and during valsalva. While there was no correlation between resting supine IJV cross sectional area and resting right atrial pressure, an increase in cross sectional area of less than 17% predicted an elevated RAP (12 or greater) with 90% sensitivity and 74% specificity. Valsalva induced increased of IJV >17% all but rules out high right atrial pressure of 12 or higher with 94% negative predictive value.
Pretty impressive results!
Those same researchers did a similar study in patients admitted with acute decompensated heart failure. In the 45 degree position, cross sectional area of the right internal jugular veins were measured at end expiration and during strain phase of valsalva, compared to RHC numbers. They also demonstrated similar findings, showing that a change of less than 66% cross sectional area from rest to valsalva predicted right atrial pressure with positive predictive value of 87%. They also showed that the change normalized with diuresis, and patients with normal cross sectional area change at discharge had 91% predictive value for avoiding readmission in 30 days.
These ultrasound results are interesting. For one, they provide 100% confidence that the IJV was actually assessed. For the patients that do not have a visible IJV, is that because they have normal CVP and right atrial pressures, or is their vein just not visible?
This technique can separate low and high right atrial pressures with pretty impressive accuracy. However this does not necessarily translate to elevated wedge pressure and volume overload, just as an elevated JVP does not necessarily mean they are volume overloaded, and may be strictly related to right heart disease.
These results are extremely useful and need to be coupled with other highly accurate ultrasound-acquired physical exam findings, such as pulmonary sonographic exam for B-lines and pleural effusion, and IVC collapsibility. Together these data may help improve our volume exam and reduce the need for right heart catheterizations.