Why Central Venous Pressure is not an indicator of cardiac output

Cardiac output is the amount of blood being pumped by the heart in 1 minute. 

Thus the equation is: 

Cardiac Output = Stroke volume * Heart Rate

Stroke volume depends on three determinants:

• contractility
• preload
• afterload

   

    In practice central venous pressure (CVP) is used as an indicator of preload and useful tool to guide hemodynamic therapy.

It can be used in absenсe of some conditions:

• right heart failure
• cardiac tamponade
• tension pneumothorax
• pulmonary embolism
• pulmonary hypertension
• tricuspid regurgitation
• increasing intraabdominal pressure

These conditions are associated with decreasing cardiac output.

 CVP is often a good approximation of right atrial pressure.  However, there is increasing evidence that CVP does not correlate with ventricular volume (i.e. preload) or volume-responsiveness, and so should not be used to guide intravenous fluid therapy.^[1][2]

 Conclusion: Central venous pressure can be used as a very approximate indicator of cardiac output (in the absence of CO monitor and conditions, mentioned above) but in combination with other clinical, instrumental and laboratory data.

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