Central venous pressure monitoring

In central venous pressure (CVP) monitoring, the provider or licensed independent provider inserts a catheter through a vein and advances it until its tip lies in or near the right atrium. Because no major valves lie at the junction of the vena cava and right atrium, pressure at end diastole reflects directly back to the catheter. When connected to a transducer or manometer, the catheter measures CVP, a direct reflection of right atrial pressure and an indirect measure of preload of the right ventricle.

What it does

CVP monitoring helps assess cardiac function, evaluate venous return to the heart, and determine the volume status of the body. The central venous (CV) line also provides access to a large vessel for rapid, high-volume fluid administration and enables frequent blood withdrawal for laboratory samples. For patients who are critically ill, especially those in cariogenic shock, CVP is a marker for volume status.

Intermittent or continuous?

CVP monitoring can be done either intermittently or continuously. Typically, a single lumen CVP line is used for intermittent pressure readings using a disposable plastic water manometer. CVP is recorded in centimeters of water (cm H₂O) or millimeters of mercury (mm Hg) read from manometer markings. However, more commonly, a pressure transducer system is used to measure continuous CVP. It is vital to trend the CVP measurements rather than to obtain one single measurement, because the trend gives information about a patient's clinical status.

A closer look at a central venous catheter

The below figure provides information about the parts of a CV catheter.

Obtaining CVP measurements

Follow these steps to obtain CVP measurements:

Make sure that the CV line or the proximal lumen of a pulmonary artery catheter is attached to the system. (If the patient has a CV line with multiple lumens, one lumen may be solely dedicated to continuous CVP monitoring and the other lumens may be used for fluid administration.)
Set up a pressure transducer system. Connect the nonpliable pressure tubing from the CVP catheter hub to the transducer. Then connect the flush solution container to a flush device.
To obtain values, position the patient flat. If they can't tolerate this position, elevate the bed to 30 degrees. Locate the level of the right atrium by identifying the phlebostatic axis. Zero the transducer, leveling the transducer air–fluid interface stopcock with the right atrium, as shown in the below photograph. Read the CVP value from the digital display on the monitor, and note the waveform. Make sure that the patient is still when the reading is taken to prevent artifact. Use this position (flat or 30 degrees) for all subsequent readings and when zeroing the transducer.
Intrathoracic pressure varies with respiration, which in turn impacts the CVP value. The ideal point in time at which to measure the CVP is at end expiration, when intrathoracic pressure is closest to atmospheric pressure.

Correlating CVP with cardiac function

Essentially, CVP measurements reflect events in the cardiac cycle and, thus, depict cardiac function. See the flow chart below for more information.

Central venous catheter pathways

The illustrations in this section show several common pathways for CV catheter insertion. Typically, a CV catheter is inserted in either the subclavian or internal jugular vein.

Follow the wave

Understanding the CVP waveform: Comparing electrical activity

When the CV catheter is attached to a pressure monitoring system, the bedside monitor can usually display digital pressure values, CVP waveforms, and electrocardiogram (ECG) tracings. Synchronizing the CVP waveform with the ECG helps you identify components of the tracing. Keep in mind that cardiac electrical activity precedes the mechanical activities of systole and diastole.

The P wave on the ECG reflects atrial depolarization, which is then followed by atrial contraction and increased atrial pressure. Corresponding to the PR interval on the ECG, the wave sequence on the CVP waveform represents atrial contraction.

The x descent on the CVP waveform represents atrial relaxation and declining pressure after systole, when the atrium expels blood into the ventricle. As the cardiac cycle progresses, the tricuspid valve closes, producing a small backward bulge known as the c wave.

The atrium filling with venous blood during diastole produces another rise in pressure and a v wave, which corresponds to the T wave of the ECG.

After atrial filling, the tricuspid valve opens. Most of the blood in the right atrium passively empties into the right ventricle, causing atrial pressure to fall. On the CVP waveform, this decline appears as the y descent.

The a and v waves are almost the same height, indicating that atrial systole and atrial diastole produce about the same amount of pressure. Consequently, right atrial pressures are recorded as mean values because they are almost the same.

Follow the wave

Normal CVP waveforms

The following figures show normal waveforms.

Follow the wave

Abnormal CVP waveforms

Elevated a wave

Physiologic causes

Increased resistance to ventricular filling
Increased atrial contraction

Associated conditions

Heart failure
Tricuspid stenosis
Pulmonary hypertension

Elevated v wave

Physiologic cause

Regurgitant flow such as in mitral regurgitation

Associated conditions

Tricuspid insufficiency/regurgitation
Inadequate closure of the tricuspid valve due to heart failure

Elevated a and v waves

Physiologic causes

Increased resistance to ventricular filling, which causes an elevated a wave
Functional regurgitation, which causes an elevated v wave

Associated conditions

Cardiac tamponade (smaller y descent than x descent)
Constrictive pericardial disease (y descent exceeds x descent)
Heart failure
Hypervolemia
Atrial hypertrophy

Absent a wave

Physiologic cause

Decreased or absent atrial contraction

Associated conditions

Atrial fibrillation
Junctional arrhythmias
Ventricular pacing

Understanding CVP ⬆ ⬇

CVP or right atrial pressure shows right ventricular function and end-diastolic pressure.

Causes of increased and decreased CVP

The following figure shows causes of increased pressure, normal values, and causes of decreased pressure.

Key points of CVP

The importance of CVP is that it indicates how the heart is interacting with the return of blood to the heart.
The CVP value just before the onset of systole is an indication of the preload of the right heart.
Normal CVP is very low.
Under normal conditions, preload is not a major determinant of cardiac output but rather serves to provide fine-tuning of cardiac output.
CVP values should not be used in isolation but rather in the context of the clinical situation and, preferably, with a measure of cardiac output.

(Bullet points reprinted with permission from Magder, S. (2015, October). Understanding central venous pressure: Not a preload index? Current Opinion in Critical Care, 21(5), 369–375. https://doi.org/10.1097/MCC.0000000000000238, Wolters Kluwer.)

Measuring CVP with a water manometer

To obtain accurate CVP readings, ensure that the manometer base is aligned with the patient's right atrium (the zero reference point). The manometer set usually contains a leveling rod to allow you to determine this alignment quickly.

After adjusting the manometer's position, examine the three-way stopcock. By turning it to any position shown in the figure that follows, you can control the direction of fluid flow. Four-way stopcocks are also available.

Converting pressure values

Although most facilities today use the pressure transducer system to measure CVP, the water manometer-the first device developed for monitoring CVP-may still be in use in some facilities. Both methods measure right atrial pressure-the pressure transducer in mm Hg and the water manometer in cm H₂O. If your facility uses both pressure transducers and water manometers, you may have to convert pressure values. Use this formula to convert cm H₂O to mm Hg:

Conversely, use this formula to change mm Hg to cm H₂O:

Minimizing complications of CVP monitoring

Be on the lookout for complications that may arise, and reference the following table for troubleshooting tips.

Problem	Signs and symptoms	Possible causes	Nursing interventions	Prevention
Infection	Redness, warmth, tenderness, swelling at the insertion or exit site Possible exudate of purulent material Local rash or pustules Fever, chills, malaise Leukocytosis	Failure to maintain sterile technique during catheter insertion or care Wet or soiled dressing remaining on site Immunosuppression Contaminated catheter or solution Frequent opening of the catheter or long-term use of a single IV access site Failure to use good antiseptic technique when accessing the IV port	Monitor vital signs closely. Re-dress the site using sterile technique. Use a chlorhexidine-impregnated sponge at the insertion site. Treat systemically with antibiotics or antifungals, depending on culture results. Catheter may be removed. Draw central and peripheral blood cultures; if the same organism appears in both, then the catheter is the primary source and should be removed. If cultures do not match but are positive, the catheter may be removed or the infection may be treated through the catheter. If the catheter is removed, culture its tip per facility policy. Document interventions.	Maintain sterile technique. Use sterile gloves, masks, and gowns when appropriate. Clean the port per facility policy before injecting or withdrawing. Observe dressing-change protocols. Change a wet or soiled dressing immediately. Change the dressing more frequently if catheter is located in femoral area or near tracheostomy. Perform tracheostomy care after catheter care. Examine solution for cloudiness and turbidity before infusing; check the fluid container for leaks. The catheter may be changed frequently. Keep the system closed as much as possible.
Pneumothorax, hemothorax, chylothorax, hydrothorax	Decreased breath sounds on the affected side With hemothorax, decreased hemoglobin level because of blood pooling Abnormal chest x-ray	Repeated or long-term use of the same vein Preexisting cardiovascular disease Lung puncture by catheter during insertion or during exchange over a guide wire Large blood vessel puncture with bleeding inside or outside the lung Lymph node puncture with leakage of lymph fluid Infusion of solution into chest area through an infiltrated catheter	Notify the physician/provider. Remove the catheter or assist with its removal. Administer oxygen as ordered. Set up and assist with chest tube insertion. Document interventions.	Position the patient head down with a rolled towel between the scapulae to dilate and expose the internal jugular or subclavian vein as much as possible during catheter insertion. Assess for early signs of fluid infiltration (swelling in the shoulder, neck, chest, and arm). Make sure that the patient is immobilized and prepared for insertion. An active patient may need to be sedated or taken to the operating room or interventional radiology.
Air embolism	Respiratory distress Unequal breath sounds Weak pulse Increased CVP Decreased blood pressure Alteration or loss of consciousness	Intake of air into the CV system during catheter insertion or tubing changes, or inadvertent opening, cutting, or breaking of catheter	Clamp the catheter immediately. Turn the patient on the left side, head down, so that air can enter the right atrium. Maintain this position for 20–30 minutes. Avoid Valsalva maneuver because a large air intake worsens the condition. Administer oxygen. Notify the physician/provider. Document interventions.	Purge all air from the tubing before hookup. Teach the patient to perform the Valsalva maneuver during catheter insertion and tubing changes. Use air-eliminating filters. Use an infusion pump with air detection capability. Use Luer-lock tubing or use locking devices for all connections.
Thrombosis	Edema at puncture site Erythema Ipsilateral swelling of arm, neck, and face Pain along vein Fever, malaise Chest pain Dyspnea Cyanosis	Sluggish flow rate Composition of catheter material (polyvinyl chloride [PVC] catheters are more thrombogenic) Hypercoagulable state of patient (conditions like cancer, pregnancy, liver failure) Preexisting limb edema Infusion of irritating solutions	Notify the physician/provider. Possibly remove the catheter. Consider treatment with anticoagulation or thrombolysis. Verify thrombosis with diagnostic studies. Apply warm, wet compresses locally. Do not use the limb on the affected side for subsequent venipuncture or blood pressure measurement. Document interventions.	Maintain a steady flow rate with the infusion pump, or flush the catheter at regular intervals. Use catheters made of less thrombogenic materials or catheters coated to prevent thrombosis. Dilute irritating solutions. Use a 0.22 micron filter for infusions.

Quick quiz ⬆ ⬇

Show and tell

Identify the CV catheter insertion site in each illustration.

1 ____________________

2 ____________________

3 ____________________

See Answer

Matchmaker

elevated a waves ____________________
A.
B.
C.
D.
absent a waves _____________________
A.
B.
C.
D.
elevated v waves ____________________
A.
B.
C.
D.
elevated a and v waves ______________
A.
B.
C.
D.

section name header

Understanding central venous pressure monitoring ⬇

Understanding CVP ⬆ ⬇

Quick quiz ⬆ ⬇

Selected references ⬆