Central venous pressure (CVP)
Central venous pressure is measured in the superior and inferior vena cava. Its value directly reflects the pressure in the right atrium.
Normal CVP is 4–10 cm $H_2O$. An increase in this parameter indicates pulmonary hypertension. Clinically, this manifests as engorgement of peripheral veins (especially the jugular veins in the neck) as blood has difficulty entering the right side of the heart.
Main causes of elevated CVP:
- Right ventricular failure of any etiology.
- Tricuspid valve disorders.
- Constrictive pericarditis.
How venous pressure is assessed
Methods of assessment are divided into approximate, clinical, and precise instrumental methods.
Approximate method (using hand veins) The physician evaluates the blood filling of the hand veins relative to the level of the left atrium. If the hand is at this level or lower, the veins become distinctly engorged. If the hand is raised more than 10 cm above the atrium, the veins should visibly collapse.
Clinical determination of CVP via jugular veins The jugular veins directly communicate with the right atrium. For the measurement, the patient lies supine (optimally at a 60° angle if hypertension is suspected), with the head turned to the side. The physician uses a vertical ruler to measure the height of the venous pulsation column above the sternal angle (angle of Louis). Normally, the height of pulsation does not exceed 3–4 cm. 5 cm is added to the resulting figure, which is the anatomical distance from the sternal angle to the center of the atrium. The final normal value is 8–9 cm $H_2O$.
Instrumental methods
- Direct phlebotanometry. An apparatus with a glass tube (Ø 1.5 mm) and a scale, filled with a sterile isotonic solution, is used. The patient lies down, and the zero point is set at the lower edge of the pectoralis major muscle. The median cubital vein is punctured. Normal: 60–100 mm $H_2O$.
- Hydrostatic method. Used in intensive care units when a subclavian vein catheter is in place. The infusion set with the solution is disconnected from the bottle, and the fluid level in the tube shows the CVP in centimeters of water.
- Electromanometry. The most accurate method using transducers during right heart catheterization.
Venous pulse and normal phlebogram
Phlebography is the graphical recording of the venous pulse, which reflects the contractile function of the right heart chambers. Before recording, it is important to differentiate jugular vein pulsation from the carotid artery: the arterial pulse has a rapid upstroke and slow downstroke, whereas the venous pulse has the opposite—a sluggish, slow upstroke and a rapid downstroke (collapse).
The transducer is placed above the clavicle at the lateral border of the sternocleidomastoid muscle. The normal curve ("negative" or atrial pulse) has three positive waves:
- Wave a (atrium): The highest wave. Occurs due to right atrial systole. Precedes arterial pulsation and the first heart sound ($S_1$).
- Wave c (carotid): Coincides with ventricular systole. Appears as transmitted pulsation from the adjacent carotid artery.
- Wave v (venous): Reflects the filling of the right atrium with blood while the tricuspid valve is closed.
Following wave v is the diastolic descent—the tricuspid valve opens, and blood rushes into the right ventricle, decreasing venous pressure.
Pathological changes of the venous pulse
The shape of the phlebogram changes in rhythm disorders and valve defects.
- Atrial fibrillation. Wave a completely disappears on the graph because there is no effective atrial systole. The rhythm of the waves becomes irregular.
- Tricuspid regurgitation. A "positive" (ventricular) venous pulse is formed. Due to the backflow (regurgitation) of blood from the right ventricle into the atrium during systole, the curve changes its shape. It begins with an abnormally high wave v, and the upstroke of the curve begins to coincide with the main wave of the arterial pulse (sphygmogram).
Briefly: answers to topical questions
What are the causes of decreased central venous pressure?
A decrease in central venous pressure in the presented materials is associated with a reduction in circulating blood volume and a decrease in venous return to the heart.
The sources indicate the following causes of hypovolemia:
- Blood loss.
- Heat stress.
When blood volume decreases, venous return to the heart decreases, and central venous pressure characterizes the volume of venous return to the heart. In low CVP, volume replacement is used in shock treatment: plasma-substituting fluids, isotonic NaCl solution, glucose.
Waves of a normal phlebogram are easily deciphered by their Latin names: a — atrium (atrium, systole), c — carotid (carotid artery, transmitted pulsation), v — venous (venous filling with closed valve).
Class and exam questions
Why is a normal venous pulse called "negative"?
The name is due to the phase mismatch between arterial and venous blood flow. When the arterial pulse curve descends (ventricular diastole), the maximum rise is registered on the venous pulse (a-wave).
Why is 5 cm added during visual calculation of CVP on the neck?
The sternal angle (from which the physician measures the height of venous engorgement) is anatomically located approximately 5 cm above the center of the right atrium, regardless of whether the patient is lying down or standing.
What does a positive venous pulse indicate?
It is a sign of tricuspid regurgitation. Due to blood regurgitation from the right ventricle into the veins during systole, the phlebogram upstroke begins to completely coincide with the arterial pulse.
What else to study on this topic
- The influence of body tilt angle (30°, 60°, and upright position) on the accuracy of jugular vein visualization.
- Physiological factors determining venous pressure: vessel caliber, wall tone, and intrathoracic pressure.
- Principles of assembly and operation of a classical phlebotonometer with isotonic solution.
- Features of subclavian vein catheterization for CVP assessment via the hydrostatic method.
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