What you need to know about central venous pressure (CVP)?

Indications for measuring CVP are:

— monitoring hemodynamic parameters (blood pressure in the pulmonary circulation);

— monitoring the effectiveness of infusion therapy.

There are no contraindications to the procedure in the presence of a subclavian catheter.

At the preparatory stage of measuring CVP, the necessary equipment is collected: a metal ruler, clean gloves, a patient monitoring card. Then the patient is placed in a strictly horizontal position without a pillow.

The manipulation itself consists of determining the zero reference level and directly measuring the central venous pressure.

Without closing the clamp, the intravenous administration system is disconnected from the bottle with the transfused solution. The system tube, starting from the subclavian catheter, is laid along the patient’s chest to the mid-axillary line at the level of the 2-3rd intercostal space (projection of the right atrium), the free end of the tube is raised vertically upward.

When blood from the subclavian catheter stops flowing into the system tube and its horizontal level is established (the boundary between the blood and the transfused solution), the height of the blood column is measured with a metal ruler from the mid-axillary line to the horizontal level.

During blood transfusion, CVP is measured after replacing it with saline solution, otherwise it is impossible to determine the horizontal level.

At the end of the manipulation, the intravenous infusion system is reconnected to the bottle with the transfused solution, having previously displaced the air from the tube. These measurements are entered into the patient's observation chart.

CVP is determined in millimeters of water and is normally 6-12 cm H2O. Art.

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Central venous pressure (abbreviated as CVP) is an integral level that characterizes indicators in the right atrium and, partially, in the pulmonary circulation at the moment of greatest relaxation of the muscular organ. That is, diastole. It is measured in mm, but not in the column of mercury, but in the water column.

An assessment of this level is not always necessary. There are several indications. All of them, one way or another, relate to urgent, critical conditions. For example, acute heart failure, cardiogenic shock and others.

In this case, the task of diagnosis is not only to determine the severity of the disorder, but also to evaluate the effectiveness of the infusion of drugs (infusion therapy).

CVP is a kind of marker, an indicator of myocardial contractility, pumping function, and hemodynamic quality. Any deviations indicate dangerous violations. In such a situation, the condition that caused the jumps in numbers is corrected.

Norms for adult patients

As for adequate indicators, they vary widely. According to studies, the normal central venous pressure in adults is from 30 to 90-100 mm water column.

Changes in value in one direction or another indicate critical disorders in the functioning of the cardiovascular system.

Measurements are carried out using invasive methods, by catheterization of large veins, therefore they do not resort to diagnosis without sufficient grounds.

The study has undeniable advantages: clarity of the indicator, monitoring of dynamic changes in real time, the ability to assess the quality of the treatment. But highly qualified personnel are required.

Possible complications during measurement

Overhydration (infusion of an excessive amount of solution) of the body can provoke not only an increase in the level of central venous pressure, but also lead to organ damage, even death.

The following complications are most often observed with invasive methods for determining central venous pressure:

• pneumothorax;
• artery damage;
• infection.

And there are also cases with more rare, but quite serious consequences of the following plan:

• hydrothorax;
• air (or catheter) embolism;
• thrombosis;
• damage to nerve receptors;
• puncture by the end of the catheter of the superior vena cava or the right atrium with the subsequent appearance of hydromediastinum or hydropericarditis;
• perforation of the endotracheal tube cuff.

It is worth noting that if all the rules of technique for performing the method are observed, the possibility of complications occurring is minimized.

What does central venous pressure depend on?

Central venous pressure is determined by several factors:

• The volume of blood that is currently circulating in the body. If there is a lack of liquid connective tissue, after, for example, an injury, an open injury, a sharp drop in the level occurs, which indicates a decrease in the quality of the heart. The condition can result in the death of the patient if a transfusion is not performed.

Even after this, the level of central venous pressure rises and stabilizes gradually, not abruptly.

With an increase in the volume of circulating blood, against the background of pronounced edema, the pressure accordingly increases, which also does not bode well for the patient.

Such processes are also observed in a healthy person, but due to the body’s ability to self-regulate, no one notices this.

• Intensity of heart contractions. If the systole is full, the pumping function is normal, the liquid connective tissue is pumped sufficiently, the central venous pressure indicators are within adequate limits.

In critically ill patients, continuous measurement of the central venous pressure level allows one to notice the onset of a decline in myocardial contractility. That is, worsening heart failure.

Other methods do not provide such accurate results in real time.

• Central venous pressure depends on respiration, but the values ​​​​in this situation vary within normal limits. We are not talking about a static number, but about a range that is accepted in medical practice.

Some lung diseases, especially those accompanied by respiratory failure, are accompanied by abrupt changes in central venous pressure, including outside critical conditions.

These include, for example. COPD, bronchial asthma, emphysema, bronchiectasis and others. The influence of pathologies of the respiratory system on the measurement results must be taken into account.

• Situational short-term changes are possible when using diuretics. Especially loop or osmotic diuretics, vasodilating medications.

There are also physiological changes in the level of central venous pressure. In the morning, the numbers are minimal, close to the lower limit of an adequate indicator; in the evening they are much higher.

The reason is muscle movements, tension (for example, straining when coughing, physical activity).

In bedridden patients, the changes are not so noticeable, but they also exist, because vascular tone and pressure in the right atrium deviate for natural reasons.

Symptoms and possible causes of changes in normal levels

Visually, changes in the level of central venous pressure can be assessed by the appearance or absence of pulsation in the external jugular vein, which is located approximately in the middle of the neck.

Click on the picture to enlarge

In addition, signs of changes in venous pressure appear with the following changes in body position:

• vertical position - at a normal level of pressure, the veins will not stand out or pulsate;
• horizontal position, but the upper part of the body is elevated at an angle of 45 degrees (reclining) - pulsation and distinct manifestation of the veins indicate increased venous pressure;
• completely horizontal position of the body - if the veins are not visible and there is no pulsation, this indicates low pressure.

A clear symptom of increased central venous pressure will be swollen veins in the neck, even when the body is in an upright position. High blood pressure is also indicated by pulsation of the veins in the neck during palpation of the liver.

The level of central venous pressure depends on the following factors:

1. Circulating blood volume (CBV) - when blood volume decreases, a similar decrease in pressure occurs in the vena cava and right atrium. For example, with severe blood loss or dehydration, low or sharply negative CVP values ​​are observed.
2. The condition of the myocardium - deterioration of its contractile function can lead to stagnation of blood in the right side of the heart and the development of acute heart failure, as a result, the central venous pressure increases.
3. The condition of the lung tissue and breathing - when you exhale, venous pressure increases, and when you inhale, it decreases. Pathologies of the respiratory system and lungs lead to the development of stagnation in the organs, resulting in an increase in indicators.

Accordingly, the reasons for changes in normal venous pressure in one direction or another are various pathologies and conditions that require urgent hospitalization of the patient.

Promotion

The reasons for the increased level of central venous pressure are directly related to a sharp decrease in the contractile activity of the heart muscle or the presence of cardiovascular diseases.

Pathologies and conditions that provoke an increase in central venous pressure:

• Myocardial infarction.
• Inflammatory damage to the myocardium (myocarditis).
• Cardiogenic shock.
• Decompensated heart failure.
• Severe TBI (traumatic brain injury).
• Development of tamponade and hemopericardium due to trauma, cardiac rupture or dissection of an aortic aneurysm.
• Inflammation of the pericardium (constrictive pericarditis).
• Interruptions of heart rhythm (angina pectoris, arrhythmia, tachycardia), hypotension, hypertension.
• Pathologies of the tricuspid valve.
• Shock condition caused by exo and endotoxins of bacteria or viruses.
• Arterial pulmonary hypertension, which leads to acute right ventricular failure.
• Pulmonary embolism.
• Artificial ventilation.
• Pneumothorax due to trauma, injury or disease of the lungs.

Demotion

The main reasons for a decrease in the central venous pressure level:

• Significant blood loss (at least 10–15% of blood volume).
• Excessive vomiting and diarrhea, contributing to dehydration.
• Decreased blood volume (hypovolemia) due to septic, spinal, hemocoagulative or anaphylactic shock.
• Severe pain or fear, even anaphylaxis.
• Uncontrolled use of diuretic or diuretic drugs.
• Exposure to vasodilators (drugs that dilate peripheral blood vessels).

Pressure parameters in the central veins are usually interpreted in conjunction with clinical data and indications of additional studies prescribed by the doctor.

In some cases, the development of heart failure or compensatory vascular spasm, accompanied by bleeding, can lead to an increase in the level of central venous pressure.

Indications for monitoring

There are not many reasons for measuring central venous pressure. These are always life-threatening conditions. Among them.

• Formation of acute heart failure. Without adequate therapy, the deviation in almost 95% of cases ends in the death of the patient within a matter of hours or days. The response to the therapy is needed immediately; the high speed of data acquisition is precisely what ensures control of the central venous pressure. Another indication for assessing the level is also partially touched upon here.
• Study of the safety and effectiveness of intravenous drugs for heart failure. Dysfunction of cardiac structures requires careful infusion of pharmaceuticals, because there is a change in hemodynamics and fluid volume. It is not known how the muscular organ will react even to such a minor intervention. In case of severe insufficiency, measurement of central venous pressure is indicated as part of the therapy and to determine its safety and effectiveness.
• Assessment of the state of the cardiovascular system, pumping ability of the myocardium after surgical interventions. It is not always required, usually if there is a tendency to cardiac dysfunction, a diagnosis of heart failure has already been made, or after surgical treatment of blood vessels and abdominal structures. The task is to prevent collapse and death of the patient from spontaneous changes.
• Massive blood loss. In such a situation, even the transfusion itself carries enormous danger. Sharp jumps in central venous pressure can lead to the opposite effect: a decrease in myocardial contractility, critical heart failure, or even stoppage of organ function (asystole). Pressure control is used as a monitoring method.
• Pericardial tamponade or suspicion of this condition. The essence is the accumulation of fluid or blood in a special membrane that encloses the heart itself. If the pressure in this bag exceeds the levels in the cardiac structures, the patient will stop and die. Careful monitoring can prevent such an outcome.
• Finally, it makes sense to carry out measurements during the acute phase of blood poisoning, sepsis. To avoid the development of a shock state or timely recognition of it.

Based on objective data, specialists adjust therapy and infusion volumes.

For what pathologies is monitoring prescribed?

Indications for CVP monitoring are serious disturbances of hemodynamic processes provoked by the following pathologies:

• acute circulatory failure;
• massive blood transfusion syndrome due to severe blood loss;
• chronic heart failure requiring invasive monitoring of the response during infusion therapy;
• the threat of developing shock conditions due to severe sepsis;
• suspicion of the development of cardiac tamponade;
• monitoring the condition during and after surgery in the abdominal area.

The CVP indicator helps to correctly assess the BCC (circulating blood volume) and the ability of the myocardium to contract.

And also control of its level allows you to avoid the occurrence of water intoxication due to the introduction of too large a volume of liquid during infusion activities.

Algorithm for measuring venous pressure

The study is carried out using an invasive method.

The list of actions is as follows:

• The doctor performs a puncture (puncture) of the jugular or superior vena cava using a special catheter with a tube leading to the system. This is a phlebotonometer or the so-called Waldmann apparatus. The device is relatively old, mechanical, but has great accuracy if installed correctly and all technological diagnostic features are observed.
• The catheter is passed to the right atrium and fixed in this state. Any movements are excluded to avoid dangerous consequences.

• A system for administering solutions and infusion therapy (dropper) is connected to the device. Then begin infusions of saline solution to fill the scale. The phlebotonometer itself is positioned so that the zero line, the beginning of the reference point, is at the level of the patient’s atrium. This will eliminate false indicators and errors.

• After filling the flotonometer scale with saline solution, you can disconnect the tube leading to the infusion therapy system. After a few minutes, the device begins to show measurement results.

Although the measurement technique is old, it is still widely used in medical practice. The mechanical phlebotonometer is being replaced by electronic analogues.

They are able to build graphs and display visual indicators on the screen. In addition, they do not require such qualifications from personnel and are easier to install.

Otherwise, the algorithm for measuring CVP is the same: insertion of the catheter, fixing it, checking the technique of performing the procedure, obtaining and processing the results.

How is the measurement carried out?

In order to measure the CVP value, you can use several methods:

• measuring technique with a ruler and dropper;
• Medifix system;
• direct manometry method using a Swan-Ganz catheter;
• alternative non-invasive methods are visual determination, for example, checking for bulging veins in the neck or arms in different body positions.

However, the most common method for determining central venous pressure, characterized by accuracy and ease of use, is the Waldman apparatus (phlebotonometer).

This is a tall stand with a graduation scale, which is located along a long glass tube with an adapter, filled with saline solution.

The algorithm for measuring central venous pressure using a phlebotonometer is as follows:

1. All air bubbles are first removed from the system by opening the tap and flushing the system with saline solution. The entry of bubbles into the patient’s body is unacceptable, as it can not only lead to errors in measurements, but also provoke the occurrence of an air embolism.
2. The device is positioned so that the zero division is parallel to the right atrium.
3. To carry out the procedure, the patient takes a lying position. The height of the sternum above the surface of the bed is then measured. The resulting value is divided by three and correlated with the zero level, which is located 2/3 above the bed.
4. The phlebotonometer is connected to the infusion system using an adapter and a connecting tube that has a clamp.
5. This tube is then filled with saline and secured with a clamp to prevent possible leaks.
6. Next, the device is connected to the jugular or subclavian vein.
7. The fixing clamp is removed so that the solution begins to flow.
8. A couple of minutes after the solution arrives, the phlebometer shows its level on the scale, which is used to determine the central venous pressure.

Improved methods allow monitoring using electrical sensors, the readings and diagrams of which are displayed on the device screen.

Reasons for the increase

Among the possible factors that provoke an increase in central venous pressure:

• Heart attack. Acute nutritional disorder of the heart muscle and myocardium. It is accompanied by a critical increase not only in central venous pressure, but also in blood pressure and general dysfunction of cardiac structures. Monitoring the indicator is not always necessary; the feasibility is determined by the doctor based on the current condition of the patient.

• Cardiogenic shock. Urgent, critical disorder. Mortality even with therapy is more than 90%. As is typical for pathology, it is extremely demanding on the quality of treatment and the professionalism of doctors; the slightest mistakes cost the patient his life. Measurement of central venous pressure in cardiogenic shock is always indicated.
• Pericarditis. An accumulation of fluid (hydropericardium) or blood (hemopericardium) in a special membrane, a sac, enclosing the heart. Develops as a result of trauma, medical diagnostic or therapeutic interventions. Spontaneous formation is also possible.

In any case, control of pressure in the right atrium and pulmonary circulation is a vital measure.

• Injuries of cardiac structures. Any, especially those accompanied by a violation of the anatomical integrity of certain tissues.
• Acute heart failure. For this disease, a dangerous sharp drop in myocardial contractility and the pumping function of the muscular organ is pathognomonic (typical).

As a result, insufficient trophism of all systems and tissues is formed. There is little nutrition, as well as oxygen, ischemic processes begin, including in the heart itself, which receives useful substances along with blood through the coronary arteries.

The venous indicator increases as a result of a reflex reaction, which the body is unable to correct.

Control of central pressure is also required during decompensation of chronic heart failure, when the disease becomes actualized and enters the acute phase.

• Inflammatory lesions of the heart. In particular myocarditis. It is usually of infectious origin. An autoimmune variant is possible; the body attacks the cells of the muscular layer of the heart itself, as a result of an erroneous reaction or failure.

The condition is unstable and reacts unpredictably to the administration of intravenous drugs, therefore constant monitoring of objective indicators of central venous pressure is necessary.

These are the key reasons. However, the list is incomplete; there are other factors for changes in venous pressure. For example, severe arrhythmia with instability of the contraction frequency, brain injuries that affect the regulation of the functioning of cardiac structures.

Provocation of the disorder is possible after the development of pulmonary embolism, pneumothorax, and injuries to the respiratory system. We are talking about exceeding the level, that is, from 90-100 mm aq. pillar or more.

Anything in this range is normal; dynamic changes are bound to happen throughout the day. They are not manifestations of pathology.

This must be taken into account during continuous measurements, including in bedridden patients.

Decoding indicators

Determining the level of pressure in the central veins allows you to assess the severity of the patient’s condition and promptly recognize dangerous pathologies. To do this, you need to know not only the CVP norm, but also the reasons that can affect the parameters.

Decoding of indicators:

Due to physiology, in the third trimester of pregnancy (30-42 weeks), increased values ​​of central venous pressure are allowed, while normal values ​​vary within 5-8 cm of water. Art.

Changes in blood volume, vascular tone and cardiac activity can appear separately or in combination with each other.

Therefore, to assess the severity of a patient’s condition with heart failure, a decrease in blood volume, or hemodynamic disorders, an “express index” is often used - the ratio between CVP, heart rate and blood pressure.

Express index indicators:

Since normal CVP values ​​vary within wide limits, monitoring its level over time is considered the most significant in identifying pathologies.

To do this, tests are carried out with the introduction of different volumes of infusion solution. That is, a small amount of fluid is administered while simultaneously checking for changes in pressure levels in the central veins.

The body's response to the administration of the solution may indicate different conditions, for example:

• an increase in the parameter by more than 5 cm of water. Art. - indicates a violation of myocardial contractility, the administration of the solution is stopped;
• increase in indicator by 2 cm of water. Art. and less - indicates a decrease in blood volume, the solution is continued to be administered.

In this case, the test is carried out in several stages, since a lot of other values ​​are simultaneously assessed - blood pressure readings, daily urine output, saturation and others.

Only a specialist’s correct interpretation of the central venous pressure level over time, taking into account other indicators, will allow the correct selection of treatment methods.

Reasons for decreased central venous pressure

There are no fewer culprits for a drop in central venous pressure, but they relate to specific conditions.

• Cardiogenic shock. Oddly enough, this change can provoke both an increase and a decrease in CVP levels. Because the process itself is unstable, sharp jumps occur. This is extremely dangerous.
• Dehydration. Heavy. By restoring the volume of fluid circulating in the body, a complete cure can be achieved. But control of central venous pressure is needed to prevent acute heart failure or to stop it in time, in the initial period.
• Central venous pressure drops with other forms of shock: traumatic, anaphylactic. However, this is a consequence. When the primary cause is corrected, it is possible to stabilize the levels and bring the body back to normal. The advisability of installing a catheter and measuring CVP in such situations is controversial and is decided at the discretion of specialists.
• There may be problems in the functioning of the heart due to pulmonary embolism, acute respiratory failure. However, these are rather exceptions to the rule. Such pathological processes are mainly accompanied by jumps in central venous pressure with a parallel decrease in myocardial contractility.

Visual assessment of the patient

An increase in venous pressure can be accurately detected only by measurement results. For this you need a device, a phlebotonometer.

However, changes can be suspected through simple observation, assessment of some visual factors and palpation of blood vessels.

The following points are characteristic of an increase in the level of central venous pressure:

• Swelling of the veins in the neck. At rest, they look large, are clearly visible, and can be palpated without problems. In this case, there is no reaction to changes in body position; the reason is stagnation of blood, impaired outflow.

• When performing a special test with pressure on the right hypochondrium, the pulsation intensifies and signs of swelling become more noticeable.

These methods are not informative enough, but they are good for rough estimates.

A decrease in central venous pressure is detected somewhat more difficult, using a ruler.

The patient is placed on the couch with his head and torso elevated. Approximately 45 degrees so that the body is higher than the legs. Pulsation of the jugular veins (in the neck) should be visible at a level of 3.5-4.5 cm above the collarbone. Its absence indicates a low indicator.

As for the diagnosis of the underlying pathology, it is carried out urgently or begins after correction of the disease, partial stabilization of the condition.

The list of measures depends on the specific disorder. At a minimum, this is an ECG, blood pressure measurement, ECHO-CG, if necessary, coronography, MRI, duplex scanning, etc.

Therapeutic measures

Therapeutic measures that are carried out when the central venous pressure increases or decreases depend on the characteristics of the pathology that caused these changes, namely:

1. For myocardial infarction - stenting or thrombolytic therapy.
2. In case of cardiogenic shock - pain relief and measures aimed at correcting impaired contractility of the heart muscle.
3. For hypovolemia - infusion therapy. At the same time, the volume of the bcc is replenished. Solutions of crystalloids and colloids are used. The molecules of colloidal solutions are larger; they retain liquid in the vessels. The molecules of the crystalloid solution are smaller in structure. Their use in case of large volumes of blood loss is necessary together with colloids.
4. It is necessary to monitor the condition of the veins. If varicose veins occur, phlebotonics and compression stockings are prescribed. These measures help prevent pulmonary embolism.

Conditions accompanied by changes in venous pressure often lead to death. Therefore, it is important to immediately consult a doctor if complaints arise.

If you have diseases of the cardiovascular system, you must regularly see a doctor and undergo medical examination.

Tests that need to be carried out for heart disease include:

• general blood analysis;
• general urine analysis;
• biochemical blood test with measurement of cardiac troponins;
• electrocardiogram;
• echocardiography;
• direct consultation with a cardiologist.

Treatment methods

Treatment depends on the specific condition. So, against the background of a decrease in the volume of circulating fluid or connective tissue, intravenous solutions are administered, and if necessary, blood transfusions are prescribed.

Cardiogenic shock and heart failure are corrected symptomatically. Then the disorder is corrected (after the patient has been removed from the emergency condition).

Pericardial tamponade requires puncture, drainage of the cavity, pumping out fluid, exudate or blood.

It is important to monitor CVP levels throughout the initial treatment, reducing or increasing the dose of the drug if necessary.

How is treatment and normalization carried out?

Treatment of a patient with an increase or decrease in pressure in the veins and right atrium depends directly on the factor that provoked this condition:

1. In case of cardiovascular failure, restorative therapy of the contractility of the heart muscle is carried out.
2. For hypovolemia, administration of blood substitutes or crystalloids is prescribed.
3. Shock conditions - eliminate the cause of shock with subsequent restoration of organ function.
4. Cardiac tamponade - a puncture is performed to remove excess fluid.

To normalize and prevent central venous pressure, venotonics are prescribed, which have the following effects:

• strengthen the walls of blood vessels, making them less permeable;
• have a positive effect on the tone of the veins, increasing their elasticity;
• actively counteract inflammatory processes.

Forecast

Prospects again depend on the primary disease and the quality of the therapy provided.

• Cardiogenic shock is fatal in most cases; heart failure ends in death in almost 45-60% of situations.
• Myocarditis, the accumulation of fluid, gives a mortality rate of about 25-30%. The same applies to a heart attack.

The numbers are very approximate. Specific forecasts depend on the situation.

In medicine, CVP is used to assess heart function in emergency conditions, the dynamics of the disorder, and study the quality of therapy.

Whether monitoring of the indicator is necessary is determined by the doctor based on the details of the clinical case.

Category: Nursing in critical care/Resuscitation and intensive care for acute cardiovascular failure

In intensive care patients, great importance is attached to the value of central venous pressure (CVP). It is not only its absolute value, normally from 90 to 120 mm, that matters. water Art., but also its change in dynamics

.
To measure central venous pressure, a Waldmann apparatus is used
. The main part of this device is a pressure gauge - a glass graduated tube with a diameter of 3 mm and a length of 40-50 cm. A rubber tube extends from the lower end of the pressure gauge, which is connected to a catheter located in the central vein (subclavian or jugular). The device is filled with sterile isotonic sodium chloride solution. The patient lies on his back in a strictly horizontal position. The term "CVP" refers to pressure in the right atrium. The projection of the right atrium corresponds to the border of the upper and middle third of the anteroposterior size of the chest in a lying person. At this level the zero mark of the pressure gauge is set. When connecting the Waldmann apparatus to a venous catheter, the fluid level in the manometer will show the CVP in mm. water Art..

See resuscitation and intensive care for acute cardiovascular failure

1. Zaryanskaya V. G. Fundamentals of resuscitation and anesthesiology for medical colleges (2nd ed.) / Series 'Secondary vocational education'. - Rostov n/D: Phoenix, 2004.
2. Barykina N.V. Nursing in surgery: textbook. allowance/N. V. Barykina, V. G. Zaryanskaya.- Ed. 14th. - Rostov n/d: Phoenix, 2013.

• Position the patient so that he can clearly see the internal jugular veins and their pulsation. It is recommended to start the study with the head positioned at an angle of 45°, but in fact the angle does not matter, the main thing is that the veins are well visualized. If it is not possible to see the internal jugular veins, CVP is measured on the external ones.

• Determine the highest point of pulsation of the internal jugular vein (the "meniscus"), which is usually visible during exhalation and coincides with the maximum of the A and V waves. This will act as a bedside pressure gauge.

• Find the angle of Louis (where the manubrium meets the body of the sternum). This point is taken as “zero” when determining the pressure in the jugular vein (JVP), in contrast to the standard point for measuring CVP - the center of the right atrium.

• Measure the vertical distance in centimeters from the sternal angle to the point of maximum pulsation of the veins. To do this, place two rulers at right angles: one horizontally (parallel to the meniscus), and the other vertically, touching the first ruler and the angle of the sternum. The distance between the angle of the sternum and the meniscus will be equal to the central venous pressure.

• To obtain the CVP value, add 5 cm to the NVP.

The method is based on the fact that the center of the right atrium (where venous pressure is assumed to be zero) is approximately five centimeters below the sternal angle. This ratio is typical for people with normal build and height, and does not depend on body position.

Thus, when using the sternum angle as a reference point, the vertical distance in centimeters to the top of the blood column in the jugular vein is equal to the PUD. Adding 5 cm to the JVP allows you to get the CVP value.

How to pronounce a surname correctly: “Louis” or “Lewis”?

It depends on situation. If you mean the angle of the sternum, then you should pronounce it in the French manner, since the term was proposed by the French surgeon Antoine Louis who first described it (Dr. Louis is better known for his joint invention with the therapist Joseph-Ignace Guillotin, which cut off the heads of aristocrats just above the angle of the sternum) .

If you are talking about the procedure for measuring CVP relative to the angle of the sternum, then you should pronounce the surname in the English manner, since it was the British doctor Sir Thomas Lewis (a student of MacKenzie) who first discovered that normally the pulsation of the jugular veins is visible 2-3 cm above the angle of Louis.

Subsequently, this technique (estimation of central venous pressure by adding 5 cm vertically relative to the level of the internal jugular veins above the angle of Louis) was called the “Lewis method”. So it doesn't really matter what you call it, both names are correct.

What is the normal value of central venous pressure?

When assessed using the Lewis method, a normal central venous pressure should be less than 7 cm water column (some experts suggest a value of 8 cm water column). This means that the jugular venous pressure (i.e. pulse pressure) should not exceed 2-3 cm (two fingers' width) above the angle of Louis.

How can you assess central venous pressure even faster?

A wonderful, quick and convenient method is to sit the patient down. If the veins of the neck are visible in a sitting patient, it means that his central venous pressure exceeds 7 cm of water. Art., which is a pathology. The collarbones are located 2 cm above the angle of the sternum, which means that with normal central venous pressure the veins behind them will not be visible.

5. Are there alternative methods for determining central venous pressure?

Yes, but they are not sufficiently tested:

• von Recklinghausen method

. The patient, who is in a supine position, is asked to place the palm of one hand on the thigh, and the palm of the second on the bed (i.e., 5-10 cm below the first hand). If the veins in both arms are swollen, then the central venous pressure is increased. If, on the contrary, the veins are swollen only in the lower arm, the central venous pressure can be considered normal.

• Alternative but similar method

consists of examining the veins of the back of the hand while slowly passively raising the arm of the patient lying on his back. The height of the level at which the veins collapse is measured in relation to the Louis angle. This value is taken equal to the central venous pressure.

Both methods may produce falsely high CVP values ​​due to local obstruction or constriction of the peripheral veins. Therefore, these methods are not recommended for widespread use.

6. How accurate is the clinical measurement of CVP?

If done correctly (and if the patient is stable), the measurement can be very accurate. The results of an approximate assessment of central venous pressure at the patient's bedside in 90% of cases differ from the indicators obtained during venous catheterization by no more than 4 cm of water. Art. However, the results obtained by different researchers (and by the same researcher) may differ by 7 cm of water. Art.

The problem becomes especially relevant in the unstable condition of the patient, in which the accuracy of the assessment plays a critical role. For example:

• When examining 50 patients in intensive care units, CVP indicators coincided very accurately among students and resident doctors, less often among students and consultant doctors, and even less often among residents and staff doctors. Factors that influenced the accuracy of the assessment included: changes in the patient's body position, poor external lighting, confusion between the determination of venous and carotid pulsations, and changes in central venous pressure during breathing.

• During the second study, a consultant physician, an intensive care unit employee, a resident, an intern and a student assessed CVP in 62 patients on a scale: low, normal, high, very high. The responses were compared with the results of right heart catheterization. The sensitivity of the clinical study was 0.33, 0.33 and 0.49 for low (7 mmHg) CVP, respectively. The specificity of the study was found to be 0.73, 0.62 and 0.76, respectively.

The measurement accuracy was higher with a low cardiac index (18 mmHg). Measurements were less accurate in patients who were in a coma or on mechanical ventilation. Higher reliability (interobserver agreement) did not lead to greater accuracy.

• In a third study, Eisenberg and his associates compared clinical examination data from critically ill patients with those obtained from pulmonary artery catheterization. Various hemodynamic parameters, including central venous pressure, were compared. Physicians were asked to predict, based on clinical data, whether the CVP would be 6 mmHg. Art. The results were correct only in 55% of cases. More often, doctors underestimated the CVP value (in 27% and 17% of cases, respectively).

So, what can be concluded about the clinical significance of CVP assessment?

Compared with catheterization values, clinical assessment of central venous pressure is generally inaccurate, especially in severely ill patients. For example, in the above-described examination of 50 patients who were in extremely critical condition, the overall measurement accuracy was 56%. All physicians who performed the measurements (students, residents, and staff) tended to underestimate the magnitude of the central venous pressure (see question 96), and a higher level of education did not guarantee the accuracy of the measurement.

In fact, the correlation coefficient between clinical assessment of central venous pressure and venous catheterization was highest among students (0.74), slightly lower among residents (0.71), and lowest among staff physicians (0.65). The comparability of results improved slightly after excluding mechanically ventilated patients from the study, because It is believed that CVP is more reliably determined when the patient is breathing spontaneously. Therefore, assessment of CVP at the patient’s bedside can be accurate only in the following most severe cases:

• At low central venous pressure

According to clinical assessment, the likelihood of detecting low CVP during catheterization increases threefold. In this case, it becomes unlikely to obtain high CVP values.

• High central venous pressure

, measured at the bedside (pulsation of the neck veins three or more centimeters above the angle of Louis), four times increases the likelihood of obtaining high CVP values ​​during catheterization. None of the patients with clinically high CVP had low results from instrumental measurements.

• And finally, normal results of clinical evaluation of central venous pressure

diagnostically insignificant (likelihood ratio approaches 1). Thus, if a normal CVP is clinically obtained, no conclusions can be drawn regarding the patient's true CVP.

Why does clinical evaluation of central venous pressure tend to underestimate the result?

Because the partially or fully erect body position required to visualize the neck veins increases the distance between the angle of Louis and the reference point (“zero”) by 3 cm. To avoid this underestimation, many doctors measure CVP during expiration.

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