Jugular Venous Pressure
Tag: JC, CVP
Come succede con l’ascoltazione cardiaca, divenuta nei fatti desueta e poco utilizzata nella pratica clinica altri aspetti dell’EO sono stati dimenticati e sempre meno praticati.
La Stanford Univerity ha un interessante progetto sull’importanza di “recuperare” alla pratica alcune manovre cliniche estremamente utili e finite nell’oblio. Il progetto ha per nome <Standford Medicine 25 — promoting the Culture of Bedside Medicine> e il suo ispiratore è Abraham Verghese.
Il sito del progetto (visitatelo) è ricco di spunti molto interessanti anche se tutto orientato all’adulto.
Personalmente l’ho utilizzato per imparare una manovra molto utile e che in più di un’occasione mi è stata d’aiuto per monitorizzare l’IC della mia anziana mamma. È la manovra che segnalo nell’ultimo video di questa scheda “Measuring Central Venous Pressure Using a Patient’s Arm”.
La scheda sintetizza il personale percorso di studio che ho dovuto “interamente rifare” per “capire a fondo” l’importanza della manovra ed è un esempio di quanta strada bisogna “rifare ogni giorno” per capire davvero le conoscenze acquisite nel percorso pre-laurea.
“Estimation of jugular venous pressure using external jugular veins begins with the understanding that there is no “45 degrees” rule. Clinicians can start looking for an external jugular venous pulsation with the patient is in the sitting position. If no venous pulsation is visible, then the head of the examination table should be lowered gradually by 10–15 degrees, each time waiting for 10–15 seconds and inspecting again for the external jugular venous pulsation. If the pulsation is not visible halfway through the incline (about 40–50 degrees) the clinician may do two things to identify the paths of the external jugular veins. First, gentle pressure at the base of the neck will cause venous distension and, second, pressure on the abdomen may cause venous pulsation to be visible. The incline of the bed may be gradually lowered to zero degrees until the venous pulsation is visible.”
The JVP aids in the estimation of volume status.
The external (EJV) or internal (IJV) jugular vein may be used.
The IJV is preferred for monitoring Central Venous Pressure by catheter insertion because the EJV is valved and not directly in line with the SVC and right atrium.
The EJV is easier to visualize when distended, and its appearance can help to discriminate between low and high central venous pressure (CVP).
When hypovolemia is suspected as a cause of hypotension, the patient may need to be lowered to a supine position to gauge the waveform in the right supraclavicular fossa.
The venous waveform can sometimes be difficult to distinguish from the carotid artery pulse. The venous waveform has several characteristic features and its individual components can usually be identified. The a and v waves, and x and y descents, are defined by their temporal relation to electrocardiographic events and heart sounds (S1 and S2, plus S3 and S4 as defined further on).
The estimated height of the venous pressure indicates the CVP or right atrial pressure. Although observers vary widely in estimation of the CVP, knowledge that the pressure is elevated, and not its specific value, can inform diagnosis and management.
The venous pressure is measured as the vertical distance between the top of the venous pulsation and the sternal inflection point, where the manubrium meets the sternum (angle of Louis). A distance of greater than 3 cm is considered abnormal, but the distance between the angle of Louis and the mid–right atrium varies considerably, especially in obese patients.
In general, use of the sternal angle as a reference leads to systematic underestimation of venous pressure. In practice, however, it is difficult to use even relatively simple landmarks, and on attempts to locate an external reference point to determine the CVP, measurements obtained by critical care nurses vary by several centimeters.
Venous pulsations above the clavicle with the patient in the sitting position are clearly abnormal, because the distance from the right atrium is at least 10 cm. Estimated CVP correlates only modestly with direct measurement. Measurements made at the bedside, in units of centimeters of blood or water, require conversion to millimeters of mercury (1.36 cm H2O = 1.0 mm Hg), for comparison with values measured with catheterization.
The venous waveforms include several distinct peaks: a, c, and v.
The a wave reflects right atrial presystolic contraction, occurs just after the electrocardiographic P wave, and precedes the first heart sound (S1). Patients with reduced right ventricular (RV) compliance from any cause can have a prominent a wave. A cannon a wave occurs with atrioventricular (AV) dissociation and right atrial contraction against a closed tricuspid valve (Fig. 11–3). The presence of cannon a waves in a patient with wide complex tachycardia identifies the rhythm as ventricular in origin. The a wave is absent with atrial fibrillation (AF).
The x descent reflects the fall in right atrial pressure after the a wave peak.
The c wave interrupts this descent as ventricular systole pushes the closed valve into the right atrium. In the neck, the carotid pulse also may contribute to the c wave.
As depicted in Figure 11-3, the x¢ descent follows because of atrial diastolic suction created by ventricular systole pulling the tricuspid valve downward. In normal persons, the x¢ descent is the predominant waveform in the jugular venous pulse.
The v wave represents atrial filling, occurs at the end of ventricular systole, and follows just after S2. Its height is determined by right atrial compliance and by the volume of blood returning to the right atrium from any source. The v wave is smaller than the a wave because of the normally compliant right atrium. In patients with ASD, the a and v waves may be of equal height; in TR, the v wave is accentuated (Video 11-1). With TR, the v wave will merge with the c wave because retrograde valve flow and antegrade right atrial filling occur simulta- neously (see Fig. 11-3).
The y descent follows the v wave peak and reflects the fall in right atrial pressure after tricuspid valve opening. Resistance to ventricular filling in early diastole blunts the y descent, as is the case with pericardial tamponade or tricuspid stenosis. The y descent will be steep when ventricular diastolic filling occurs early and rapidly, as with pericardial constriction or isolated, severe TR.
The normal venous pressure should fall by at least 3 mm Hg with inspiration. A rise in venous pressure (or its failure to decrease) with inspiration (Kussmaul sign) is associated with constrictive pericarditis, and also with restrictive cardiomyopathy, pulmonary embolism, RV infarction, and advanced systolic heart failure. A Kussmaul sign (Video 11–2) is seen with right-sided volume overload and reduced RV compliance. Normally, the inspiratory increase in right-sided venous return is accommodated by increased RV ejection, facilitated by an increase in the capacitance of the pulmonary vascular bed. In states of RV diastolic dysfunction and volume overload, the right ventricle cannot accommodate the enhanced volume, and the pressure rises.
The abdominojugular reflex or passive leg elevation can elicit venous hypertension. The abdominojugular reflex requires firm and consistent pressure over the upper abdomen, preferably the right upper quadrant, for at least 10 seconds. A sustained rise of more than 3 cm in the venous pressure for at least 15 seconds after resumption of spontaneous respiration is a positive response. The patient should be coached to refrain from holding the breath or performing a Valsalva-like maneuver, which can falsely elevate the venous pressure. The abdominojugular reflex can predict heart failure and a pulmonary artery wedge pressure higher than 15 mm Hg.
