Central Venous Pressure

Central venous pressure (CVP), also known as mean venous pressure (MVP) is the pressure of blood in the thoracic vena cava, near the right atrium of the heart. CVP reflects the amount of blood returning to the heart and the ability of the heart to pump the blood into the arterial system.

Measurement

Normal CVP can be measured from two points of reference:

• Sternum: 0–14 cm H₂O
• Midaxillary line: 8–15 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 intensive care units, facilities are available to measure CVP continuously.

Normal values vary between 4 and 12 cmH₂O。

Factors Affecting CVP

Factors that increase CVP include:

• Hypervolemia
• forced exhalation
• Tension pneumothorax
• Heart failure
• Pleural effusion
• Decreased cardiac output
• Cardiac tamponade
• Mechanical ventilation and the application of positive end-expiratory pressure (PEEP)
• Pulmonary Hypertension
• Pulmonary Embolism

Factors that decrease CVP include:

• Hypovolemia
• Deep inhalation
• Distributive shock

Insertion Sites

1. Internal jugular veins This site is chosen frequently as there is a high rate of successful insertion and a low incidence of complications such as pneumothorax. Internal jugular veins are short, straight and relatively large allowing easy access; however, catheter occlusion may occur as a result of head movement and may cause irritation in conscious patients.
2. Subclavian veins This site is often chosen as there are more recognizable anatomical landmarks, making insertion of the device easier. Because this site is positioned beneath the clavicle there is a risk of pneumothorax during insertion. A subclavian CVC is generally recommended as it is more comfortable for the patient.
3. Femoral veins This site provides rapid central access during an emergency such as a cardiac arrest. As the CVC is placed in a vein near the groin there is an increased risk of associated infection. In addition, femoral CVCs are reported to be uncomfortable and may discourage the conscious patient from moving.

Potential Complications

1. Haemorrhage – from the catheter site – if it becomes disconnected from the infusion. Patients who have coagulation problems such as those on warfarin or those will clotting disorders are at risk. Catheter occlusion – by a blood clot or kinked tube – regular flushing of the CVC line and a well secured dressing should help to avoid this.
2. Infection – redness, pain, swelling around the catheter insertion site may all indicate infection. Careful asepsis is needed when touching a CVC site. Swabs for MC&S should be taken if infection is suspected.
3. Air embolus – if the infusion or monitoring lines become disconnected there is a risk that air can enter the venous system. All lines and connections should be checked at the start of every shift to minimize the risk of this occurring.
4. Catheter displacement – if the CVC moves into the chambers of the heart then cardiac arrhythmias may be noted, and should be reported. If the CVC is no longer in the correct position, CVP readings and medication administration will be affected.

CVP Recording

Nursing and medical staff must be familiar with the equipment being used to ensure accurate readings and provide patients with appropriate care. CVP is usually recorded at the mid-axillary line where the manometer arm or transducer is level with the phlebostatic axis. This is where the fourth intercostal space and mid-axillary line cross each other allowing the measurement to be as close to the right atrium as possible.

Using A Manometer

1. Explain the procedure to the patient to gain informed consent.
2. If IV fluid is not running, ensure that the CVC is patent by flushing the catheter.
3. Place the patient flat in a supine position if possible. Alternatively, measurements can be taken with the patient in a semi-recumbent position. The position should remain the same for each measurement taken to ensure an accurate comparable result.