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Central Venous Pressure

Purpose

CVP (Central Venous Pressure) is a cardiac preload assessment measure. It’s not the best one because it can be changed by other factors than the volume status of the patient (eg: positive pressure ventilation, cardiac compliance) [1].

Measurement

Should be measured in the distal lumen of a CVC with the tip placed on a intra thoracic major vein. The pressure can be measured in many different ways. In the following description this measurement will be with a pressure transducer.

  1. Position the patient supine to a 60º angle
  2. Place and zero the transducer at a point 5 cm bellow the external angle
  3. Measure the pressure tracing on the monitor
  4. Let the monitor calculate the CVP or measure it at end expiration on the notch between the a and c curve, the z point. On his absence the pressure at ECG Q wave or the base of a can be used.

Conditions and caveats

  • On a continuos tracing the patient must always be on the same position by the transducer
  • The CVP reflects the pressure inside the heart to the atmospheric pressure and not the transmural pressure. It can be changed by changes in intrapericadial pressure as when the patient has pericardial fluid, increased abdominal or mediastinic pressure or positive pressure ventilation.
  • The measure should be done at the end of a passive expiration
  • If possible should’t be used alone to know fluid responsiveness. Better measurements are the SVV, PPV or the GEDI.

Reference Values

With the caveats above the reference values that should be targeted by the Surviving Sepsis Guidelines[2] are:

Reference
Normal 0–8mmHg
Target on Spontaneous Breathing 8–12mmHg
Target on Positive Pressure Ventilation,
Decreased Ventricular Compliance or
Abdominal Hypertension
12–15mmHg

Bibliography