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The Physiology of Central Venous Catheters
What is central venous pressure? Why is this important for anyone to know?
To answer this question, we’re going to have to go over some cardiac physiology.
- Central venous pressure (CVP) is a good approximation of right atrial pressure , which in turn is a major determinant of right ventricular end diastolic volume (or the preload of the right ventricle.) Remember that the preload is a reflection of the resting myocardial fiber length, which is also the ventricular end diastolic volume. So…
CVP ~ right atrial pressure ~ right ventricular end diastolic volume (preload )
Recall that right atrial pressure (and thus central venous pressure) is a reflection of :
- Cardiac function
- Venous return to the heart
Knowing the status of these two variables is very important when taking care of critically ill patients. However, these two variables are interrelated and influence one another, so this can make it very difficult to interpret how one (or both) may be influencing the central venous pressure we are looking at!
Let’s go back to the FRANK-STARLING CURVE (just for a minute…)
This curve looks at right atrial pressure (or preload ) in relation to cardiac output. As you can see from the graph, there can be vastly different cardiac output for the same right atrial pressure. How is this possible? Recall the 4 major determinants of cardiac function:
- Heart rate
If the right atrial pressure (preload ) stays constant, cardiac output can still be influcenced by changes in the other three factors. So while CVP alone cannot tell the whole story, it can give a good approximation of the hemodynamic status and right-sided cardiac function of the patient. Furthermore, if the patient is healthy and has good heart and lung function, the central venous pressure can provide a good estimate of the cardiac function of the left side of the heart as well.
How is CVP measured?
Once the central venous catheter is tested and secured, a calibrated transducer is connected to the catheter, and placed at the level of the right atrium. Information can be gained by not only looking at the central venous pressure, but also by the waveform produced by slight variations of pressure throughout the cardiac cycle.
Last modified on: April 21, 2005
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