Central Venous Pressure Monitoring

Central venous pressure is considered a direct measurement of the blood pressure in the right atrium and vena cava. It is acquired by threading a central venous catheter (subclavian double lumen central line shown) into any of several large veins. It is threaded so that the tip of the catheter rests in the lower third of the superior vena cava. The pressure monitoring assembly is attached to the distal port of a multilumen central vein catheter.

Normal CVP can be measured from two points of reference:
• Sternum: 0-5 cm H2O
• Midaxillary line: 5-10 cm H2O

CVP can be measured by connecting the patient's central venous catheter to a special infusion set which is connected to a small diameter water column. If the water column is calibrated properly the height of the column indicates the CVP.
In most progressive intensive care units in the U.S., specialized monitors are available to continuously measure CVP as well as other hemodynamic values.

Assisting with CVP placement
• Adhere to institutional Policy and Procedure.
• Obtain history and assess the patient.
• Explain the procedure to the patient, include:
o local anesthetic
o trendelenberg positioning
o draping
o limit movement
o need to maintain sterile field.
o post procedure chest X-ray
• Obtain a sterile, flushed and pressurized transducer assembly
• Obtain the catheter size, style and length ordered.
• Obtain supplies:
o Masks
o Sterile gloves
o Line insertion kit
o Heparin flush per policy
• Position patient supine on bed capable of trendelenberg position
• Prepare for post procedure chest X-ray

The CVP catheter is an important tool used to assess right ventricular function and systemic fluid status.
• Normal CVP is 2-6 mm Hg.
• CVP is elevated by :
o overhydration which increases venous return
o heart failure or PA stenosis which limit venous outflow and lead to venous congestion
o positive pressure breathing, straining,
• CVP decreases with:
o hypovolemic shock from hemorrhage, fluid shift, dehydration
o negative pressure breathing which occurs when the patient demonstrates retractions or mechanical negative pressure which is sometimes used for high spinal cord injuries.

The CVP catheter is also an important treatment tool which allows for:
• Rapid infusion
• Infusion of hypertonic solutions and medications that could damage veins
• Serial venous blood assessment

Factors which increase CVP include:
• Hypervolemia
• forced exhalation
• Tension pneumothorax
• Heart failure
• Pleural effusion
• Decreased cardiac output
• Cardiac tamponade

Factors which decrease CVP include:
• Hypovolemia
• Deep inhalation


There are two ways to read a CVP waveform:

1. Find the mean of the A wave.
• read the high point of the A wave
• read the low point of the A wave
• add the high point to the low point
• divide the sum by 2
• the result is the mean CVP
The A wave starts just after the P wave ends and represents the atrial contraction. The high point of the A wave is the atrial pressure at maximum contraction. During the A wave the atrial pressure is greater than the ventricular diastolic pressure. At that point, the atrium is contracted, the tricuspid is open. Therefore, the high point of the A wave closely parallels the right ventricular end diastolic pressure. Remember, when the tricuspid valve is open and the right ventricle is full, the ventricle, atrium and vena cavae are all connected. Therefore, that point is the CVP.

2. Find the Z-point.
• Find the Z-point which occurs mid to end QRS
• Read the Z-point
The Z-point coincides with the middle to end of the QRS wave. It occurs just before closure of the tricuspid valve. Therefore, it is a good indicator of right ventricular end diastolic pressure. The Z-point is useful when A waves are not visible, as in atrial fibrillation. (The c-wave occurs at closure of the tricuspid valve. The crest of the c-wave is the atrial pressure increase caused by the tricuspid valve bulging back into the atrium.)

Types
There are several types of central venous catheters:
1.Tunneled catheter
This type of catheter is inserted into a vein at one location (neck, chest or groin), and tunneled under the skin to a separate exit site, where it emerges from underneath the skin. It is held in place by a Dacron cuff, just underneath the skin at the exit site. The exit site is typically located in the chest, making the access ports less visible than if they were to directly protrude from the neck. Passing the catheter under the skin helps to prevent infection and provides stability.

2.Implanted port
This type is similar to a tunneled catheter but is left entirely under the skin. Medicines are injected through the skin into the catheter. Some implanted ports contain a small reservoir that can be refilled in the same way. After being filled, the reservoir slowly releases the medicine into the bloodstream. An implanted port is less obvious than a tunneled catheter and requires very little daily care. It has less impact on a person's activities than a PICC line or a tunneled catheter. Surgically implanted infusion port placed below othe clavicle (infraclavicular fossa), catheter threaded into the right atrium through large vein. Accessed via non-coring "Huber" needle through the skin. May need to use topical anesthetic prior to accessing port. Used for medications, chemotherapy, TPN, and blood. Easy to maintain for home-based therapy.

3. PICC line
A peripherally inserted central catheter, or PICC line (say "pick"), is a central venous catheter inserted into a vein in the arm rather than a vein in the neck or chest.


4. Technical description

Triluminal catheter
Dependent on its use, the catheter is monoluminal, biluminal or triluminal, dependent on the actual number of tubes or lumens (1, 2 and 3 respectively). Some catheters have 4 or 5 lumens, depending on the reason for their use.
The catheter is usually held in place by a suture or staple and an occlusive dressing. Regular flushing with saline or a heparin-containing solution keeps the line patent and prevents thrombosis (formation of a blood clot). Certain lines are impregnated with antibiotics, silver-containing substances (specifically silver sulfadiazine) and/or chlorhexidine to reduce infection risk.
Specific types of long-term central lines are the Hickman catheters, which require clamps to make sure the valve is closed, and Groshong catheters, which have a valve that opens as fluid is withdrawn or infused and remains closed when not in use. Hickman and Groshong lines need more specific measures to prevent infection. Hence, they are inserted into the jugular vein but then tunneled under the skin to maximize the distance a pathogen would need to travel to enter the bloodstream. Hickman lines also have a "cuff" under the skin, again to prevent bacterial migration.[citation needed]