It reflects right atrial pressure, which depends on volume, cardiac function and compliance
Expansion
Central venous pressure approximates right atrial pressure, normally 0 to 8 mmHg. It reflects the interaction of:
- Blood volume and venous tone
- Right ventricular function
- Venous compliance
- Intrathoracic pressure
Raised by: fluid overload, right ventricular failure, tricuspid regurgitation, pulmonary hypertension, cardiac tamponade, tension pneumothorax, positive pressure ventilation and PEEP.
Lowered by: hypovolaemia and vasodilatation.
The important caveat is that it is a pressure, used as a surrogate for volume. In a stiff or failing right ventricle, a high pressure can coexist with a low volume, and in a compliant one the reverse. Numerous studies show a single value does not predict who will respond to fluid.
More reliable indicators of fluid responsiveness are dynamic measures: stroke volume variation, pulse pressure variation, the response to a passive leg raise, or the change after a defined fluid challenge.