The central venous pressure (CVP) is measured with the patient lying flat; it is expressed in cmH2O above a point level with the right atrium. The normal value is 0-8 cmH2O. Clinically, it is useful as an indication of right ventricular preload. A volume challenge of 250-500 ml crystalloid causing an increase in CVP that is not sustained for more than 10 minutes suggests hypovolaemia, for example. Serial readings (i.e. the trend of CVP measurements) are thus far more useful than single readings.
Increased intrathoracic pressure
Impaired cardiac function (failure, tamponade. Only useful for information regarding the right side of the heart).
Superior vena cava obstruction
Reduced intrathoracic pressure (e.g. inspiration)