Central venous pressure (CVP) is the blood pressure in the venae cavae, near the right atrium of the heart. CVP reflects the amount of blood returning to the heart and the ability of the heart to pump the blood back into the arterial system. Central venous pressure (CVP) (also known as: right atrial pressure; RAP).
Central Venous Pressure (CVP for short) is defined as the pressure of blood in the thoracic vena cava just before it (the blood) enters the right atrium of the heart. Normal CVP is 5 to 10 cm H2O.
CVP measurements are important in clinical cardiology because the CVP is a major determinant of the filling pressure of the right ventricle of the heart. The filling pressure of the right ventricle determines the stroke volume i.e. the amount of blood pumped with each contraction of the heart.
Central Venous Pressure is an accurate indicator of the amount of blood returning to the heart from the head, body and limbs via the superior and inferior vena cava. If and when there is blood loss then the CVP reading will be altered (will fall) almost immediately as the amount of blood returning to the heart will have decreased. Central Venous Pressure is also an accurate indicator of the ability of the heart (myocardial pump strength) to pump out blood to maintain normal blood pressure and tissue perfusion.
The CVP is an accurate indicator of right ventricular end diastolic volume. In most institutions CVP is measured in cm of water (H2O). On this scale the normal value of CVP is 5 to 10 cm H2O. Some, (very few) institutions measure CVP in mm. Hg (millimetres of mercury). On this scale the normal value is approximately 4 to 8 mm Hg.
Central Venous Pressure in measured using a sterile indwelling central venous catheter (CVC). One end of the CVC is attached to a manometer or an electronic transducer, computer and monitor. Ultrasound may be used to guide CVC insertion.
Central Venous Pressure monitoring is more accurate then blood pressure monitoring because changes in circulating volume will be reflected in changes in CVP values as soon as there is blood loss.
When there is overloading of the circulatory system or there is heart failure the CVP rises. However, when there is dehydration (e.g. diabetes insipidus), fluid loss due to bleeding or shifting of fluids within the body compartments (e.g. shock) then the CVP will fall.
Conversely, when the CVP is falling there may be a decrease in urinary output and the patient may complain of feeling excessively thirsty. To correct over hydration, as illustrated by a rising CVP the physician may choose to restrict fluids or to administer a diuretic. To deal with a falling CVP the physician might choose to give the patient more fluids or blood as the case may be
Factors affecting CVP
Factors that increase CVP include..
- forced exhalation
- Tension pneumothorax
- Heart failure
- Pleural effusion
- Decreased cardiac output
- Cardiac tamponade
- Mechanical ventilation and the application of positive end-expiratory pressure (PEEP)
Factors that decrease CVP include..
- Deep inhalation
- Distributive shock