In this age of technological marvels, it is easy to become so reliant on them as to neglect the value of bedside physical signs. Yet these signs provide information that adds no cost, is immediately available, and can be repeated at will.
Few physical findings are as useful but as undervalued as is the estimation of the jugular venous pressure. Unfortunately, many practitioners at many levels of seniority and experience do not measure it correctly, leading to a vicious circle of unreliable information, lack of confidence, and underuse. Another reason for its underuse is that the jugular venous pressure does not correlate precisely with the right atrial pressure, as we will see below.
In this review, we will attempt to clarify physiologic principles and describe technical details. Much of this is simple but, as always, the devil is in the details.
Think of the systemic veins as a soft-walled and mildly distensible reservoir with fingerlike projections, analogous to a partially fluidfilled surgical glove.1 In a semi-upright position, the venous system is partially filled with blood and is collapsed above the level that this blood reaches up to.
Blood is constantly flowing in and out of this reservoir, flowing in by venous return and flowing out by the pumping action of the right side of the heart. The volume in the venous reservoir and hence the pressure are normally maintained by the variability of right ventricular stroke volume in accordance with the Frank-Starling law. Excess volume and pressure indicate failure of this homeostatic mechanism.
The internal jugular veins, being continuous with the superior vena cava, provide a visible measure of the degree to which the systemic venous reservoir is filled, a manometer that reflects the pressure in the right atrium—at least in theory.2 Thus, the vertical height above the right atrium to which they are distended and above which they are in a collapsed state should reflect the right atrial pressure.
(In fact, the jugular venous pressure may underestimate the right atrial pressure, for reasons still not understood. This will be discussed below.)
In a healthy person, the visible jugular veins are fully collapsed when the person is standing and are often distended to a variable degree when the person is supine. Selecting an appropriate intermediate position permits the top of the column (the meniscus) to become visible in the neck between the clavicle and the mandible.
DISCREPANCY BETWEEN JUGULAR VENOUS AND RIGHT ATRIAL PRESSURE
Several reports have indicated that the jugular venous pressure may underestimate the right atrial pressure. Deol et al3 confirmed this, while establishing an excellent correlation between the level of venous collapse (observed on ultrasonography) and the jugular venous pressure. The difference between the right atrial pressure and the jugular venous pressure tended to be greater at higher venous pressures.3
Most people have a valve near the termination of the internal jugular vein, with variable competence. Inhibition of reflux of blood from the superior vena cava into the internal jugular vein by this valve is the most plausible cause of this disparity.4
The failure of the jugular venous pressure to correlate with the right atrial pressure has been cited by some as a reason to doubt the value of a sign that cardiologists have long relied on. How do we reconcile this apparent paradox? Careful review of the literature that has demonstrated this lack of correlation reveals the following:
- When unequal, the jugular venous pressure always underestimates the right atrial pressure.
- The lack of correlation is less evident at lower venous pressures.
This indicates the following:
- In the presence of congestive heart failure, the right atrial pressure is at least as high and perhaps higher than the jugular venous pressure. Hence, if the jugular venous pressure is high, further treatment, especially diuresis, is needed.
- A jugular venous pressure of zero implies a euvolemic state.
Thus, the jugular venous pressure provides excellent guidance when administering diuresis in congestive heart failure. These deductions obviously require the clinical judgment that the elevated right atrial pressure and jugular venous pressure do indeed reflect elevation of pulmonary capillary wedge pressure rather than other conditions discussed later in this article.