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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