Central venous pressure (CVP) is the pressure within the thoracic vena cava near the right atrium of the heart, and it reflects the amount of blood returning to the heart and the ability of the heart to pump the blood into the arterial system. The determinants of CVP include:
1. Blood Volume
- Increased Blood Volume: An increase in the total blood volume, such as through intravenous fluid administration, increases CVP.
- Decreased Blood Volume: Hypovolaemia, due to bleeding, dehydration, or other causes, decreases CVP.
2. Venous Tone
- Vasoconstriction: Increased sympathetic stimulation can cause vasoconstriction, which raises CVP.
- Vasodilation: Conditions that lead to vasodilation, such as certain medications or shock, can lower CVP.
3. Intrathoracic Pressure
- Positive Intrathoracic Pressure: Conditions such as positive pressure ventilation or tension pneumothorax can increase intrathoracic pressure, thereby increasing CVP.
- Negative Intrathoracic Pressure: Deep inspiration or conditions reducing intrathoracic pressure can decrease CVP.
- Respiratory Efforts:
- Valsalva Maneuver: Increases intrathoracic pressure, raising CVP temporarily.
- Inspiration: Negative intrathoracic pressure during inspiration can transiently decrease CVP.
4. Cardiac Function
- Right Ventricular Function: If the right ventricle is failing or there is right ventricular infarction, CVP increases due to impaired blood ejection.
- Left Heart Failure: This can lead to an increase in pulmonary pressures and subsequently increased CVP.
5. Venous Return
- Position of the Patient: Lying down increases venous return compared to standing up, which can elevate CVP.
- Gravity and Body Position: Changing body position affects the hydrostatic pressure and hence the venous return to the heart.
6. Abdominal Pressure
- Increased Abdominal Pressure: Conditions like abdominal compartment syndrome or obesity can increase intra-abdominal pressure, thus increasing CVP.
- Decreased Abdominal Pressure: Reduction in abdominal pressure can decrease CVP.
7. Obstruction of Venous Return
- Conditions like Superior Vena Cava Syndrome: Any obstruction in the venous system, such as from a tumor or thrombus, can increase CVP.
8. Compliance of the Venous System
- Increased Compliance: A more compliant venous system can accommodate more blood without a significant rise in pressure, which can lower CVP.
- Decreased Compliance: Conditions such as scarring or fibrosis of the venous system can decrease compliance, raising CVP.
Additinally
Pulmonary Hypertension:
- Increased Pulmonary Arterial Pressure: When the pressure in the pulmonary artery is elevated, the right ventricle has to work harder to pump blood into the lungs. This can lead to right ventricular hypertrophy and eventual right heart failure, both of which can elevate CVP.
Pulmonary Embolism:
- Obstruction of Pulmonary Artery: A pulmonary embolism blocks blood flow in the pulmonary artery, increasing resistance and pressure in the pulmonary circulation. This raises the workload on the right ventricle, potentially leading to right heart failure and increased CVP.
Pulmonary Valve Stenosis:
- Obstructed Outflow: A narrowed pulmonary valve restricts blood flow from the right ventricle to the pulmonary artery. This causes increased pressure in the right ventricle and right atrium, elevating CVP.
Cor Pulmonale:
- Right Heart Failure due to Lung Disease: Chronic lung diseases, such as chronic obstructive pulmonary disease (COPD) or interstitial lung disease, can lead to increased pulmonary artery pressures (secondary pulmonary hypertension). This condition, known as cor pulmonale, results in right ventricular enlargement and increased CVP.
Congenital Heart Defects:
- Structural Abnormalities: Certain congenital heart defects that involve the pulmonary artery or its connections can alter pressures within the right heart chambers, subsequently affecting CVP. For instance, Tetralogy of Fallot or transposition of the great arteries can lead to abnormal pressure dynamics that influence CVP.