Monitoring central venous pressure

Central venous pressure (CVP) is the pressure in the right atrium of the heart (Mooney and Comerford, 2003). It is measured by inserting a central venous catheter into the right atrium and connecting it to a manometer. The indications for monitoring a patient’s CVP (Mooney and Comerford, 2003) are:

• to monitor haemodynamic status in patients who are critically ill
• to monitor patients postoperatively
• to facilitate the diagnosis of cardiac failure
• to administer intravenous medication where the medication is an irritant when give by peripheral infusion (to monitor its effects on CVP)
• to administer large volumes of fluid (to monitor their effect on CVP in situations such as shock)
• to administer parenteral nutrition

A ‘normal’ CVP reading can vary, so when you are recording a measurement it is important to ascertain at what range the medical team would like readings to be maintained. Research suggests that a simple manometer set gives a range of 3–12cmH2O, whereas with a transducer set the normal range is 0–8mmHg. It is also important to take serial readings to establish a trend, so that abnormalities can be detected (Hatchett, 2000).

With advances in medical technology, CVP measurements are now normally measured with a transducer set, particularly in critical care environments. If these facilities are not available, measurements can however be taken manually. 

The CVP measurement can be taken from either the mid-axilla (so that the baseline of the manometer set is in line with the right atrium) or the sternal notch. However, it is important to take readings from one position to ensure accuracy of the result. Readings taken for the sternal notch are about 5cmH2O lower than those taken from the mid-axilla.

The equipment required consists of:

• infusion stand
• manometer set
• bag of fluid for readings (normally 0.9% sodium chloride)
• spirit level

Procedure for central venous pressure measurement

1. Explain the procedure to the patient and gain his/her consent
2. Gather the necessary equipment
3. Connect the manometer set to the infusion stand, and run the fluid through the infusion line (always seek advice if you are unsure of the procedure)
4. Use the spirit level to make sure that the patient is level with the zero marker on the manometer set to ensure an accurate result
5. Turn off the three-way tap to the patient. This will allow the manometer to fill slowly with fluid from the infusion bag. Do not overfill the chamber
6. Turn off the three-way tap to the infusion fluid. This will cause the fluid in the manometer set to fall
7. The reading can be taken when the level of fluid stops falling and settles to a rise and fall with the patient’s respiration
8. Record the CVP reading on the patient’s observation chart

References

Hatchett R. Central venous pressure measurements. Nursing Times. 2000; 96(15): 49–50

Mooney G, Comerford D. What you need to know about central venous lines. Nursing Times. 2003; 99(10): 28–9