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Abnormal Central Venous Pressure: David L. Simel, MD, MHS, discusses the clinical examination for abnormal central venous pressure.
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Abnormal Central Venous Pressure: David L. Simel, MD, MHS, discusses the clinical examination for abnormal central venous pressure.
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Segment:0 .
>> I'm Joan Stephenson, Editor of JAMA's Medical News and Perspectives Section. Today I have the pleasure of once again speaking with Dr. David Simel, this time on the topic of assessing central venous pressure, which is discussed in a chapter of the Rational Clinical Exam. Welcome back to the podcast, Dr. Simel, and please introduce yourself to our listeners. >> I am David Simel. I'm the Editor of the Rational Clinical Exam Series, and I'm a Professor of Medicine at Duke University in the Durham Veterans Affairs Medical Center.
>> Dr. Simel, what information can evaluation of the jugular venous pulse provide to the clinician? >> Well, the jugular venous pulse gives us clues about the central venous pressure, and from that we infer the patient's intravascular volume status. Typically, what we are trying to do is figure out if the central venous pressure is high, or whether the central venous pressure is low. And this works because the jugular veins act as manometer tubes for the right atrium and they display changes in blood flow and pressure caused by right atrial filling, contraction, and emptying.
When we estimate the central venous pressure from the jugular venous pulse, we have to be able to identify the top of the pulse, but that can be difficult to see the venous pulsation in some patients, and this can be particularly true in patients with short or fat necks, or in those patients with a low central venous pressure. >> Which jugular vein should be used to estimate central venous pressure, and how should the patient be positioned during the examination? >> Well, the most distinct, undamped waveform is going to be seen in the right internal jugular vein, and so it is the vein that most accurately reflects the right atrial pressure because it's directly in line with the right atrium.
Now, the external jugular veins can be easier to see, but they may be constricted as they pass through the fascial planes of the neck, and so most experts feel that they do not as accurately reflect the right atrial pressure. However, there is a study that suggests that the only significant difference between the central venous pressure from the external versus the internal jugular vein occurs in patients on mechanical ventilators. >> How can clinicians differentiate between carotid arterial pulse and jugular venous pulse?
>> Well, initially there can be some confusion, but it's not too difficult to sort out. First you have to address the position of the patient. So the patient's head is supported to relax their neck muscles with the trunk inclined at an angle that brings the top of the column of the blood in the internal jugular vein to a level that's going to be above the clavicle, but below the angle of the jaw. Now, in normal subjects this is going to be at about 30 to 45 degrees above the horizontal.
In patients with volume overload, the position may need to be more upright. And conversely, in patients with a low intravascular volume, in order to see the pulse, you may need to have the patient closer to horizontal. So once you get the patient in the right position, the venous pulsation is seen as a diffuse column, usually it has two waves, and the upward deflection of those waves is slow. The carotid pulse is going to be fast and well localized with a single outward deflection.
Now, the venous pulsation will vary with position and it varies with inspiration, while the arterial pulsation is constant, despite position, and does not vary with respiration. And finally, the venous pulsation wave itself is not palpable and it disappears with slight compression. So you can use these features of a venous versus arterial wave to sort out what you're seeing. >> What steps should clinicians take to estimate central venous pressure? >> Well, after the top of the jugular vein meniscus is identified, the examiner can estimate, or from a ruler placed vertically over the sternal notch, actually measure the height of an imaginary horizontal line sighted from the ruler to the meniscus.
Now, the traditional assumption has been that the central venous pressure is going to be this height, plus 5 centimeters. However, physicians tend to underestimate the central venous pressure, and the assumption of a 5-centimeter depth from the sternal notch to the right atrium is probably not valid. In other words, the assumption is that all patients have the same 5-centimeter depth. Now, the reason we probably underestimate is because the distance from the sternal notch to the right atrium may be closer to 8 centimeters, rather than the traditionally assumed value.
So the current recommendations are that a jugular venous pressure of 3 centimeters above the sternal notch suggests an elevated central venous pressure. >> Dr. Simel, how accurate is the clinical assessment of central venous pressure? >> Well, the accuracy depends on what you're looking for. So first you have to decide what you expect based on the clinical situation. So if the clinical question is, is the intravascular volume high, then a jugular venous pressure over 3 centimeters above the sternal angle increases the odds of a high central venous pressure by threefold.
If the clinical question is instead does this patient have low intravascular volume, then the absence of any JVP, or jugular venous pressure meniscus, meaning you can't find it, increases the likelihood of low intravascular volume or a low central venous pressure also by a little over threefold. >> Is there anything else you would like to tell our listeners about the clinical examination for abnormal central venous pressure? >> Sure. I'd like to share my pearl for identifying the meniscus.
Often, I see physicians shine a penlight directly on the neck and then they look for the meniscus while using a sight line that is exactly perpendicular to the vein, and this is similar to flying in a plane over the ocean while trying to observe a tsunami. The tsunami can't be seen from that perspective. So for the venous pulse, if the physician holds a penlight obliquely so that it creates a shadow of the neck on the bedsheet, the shadow of the venous pulsations can be seen easily.
And once the pulsations are identified on the bedsheet, the shadow waveforms are easy to see. The meniscus can be located by placing a finger on the neck until the shadow of the finger is directly over the shadowed meniscus. >> Thank you, Dr. Simel, for this pearl, and also for your insights into assessing central venous pressure. For additional information about this topic, JAMAevidence subscribers can consult the Rational Clinical Examination's chapter on abnormal central venous pressure. This has been Joan Stephenson of JAMA talking with Dr. David Simel for JAMAevidence.
