central venous pressure

CVP represents the pressure of blood returning to the right atrium via the superior and inferior vena cava, serving as a surrogate for right ventricular end-diastolic volume (preload). It is measured invasively via a central venous catheter placed in the internal jugular or subclavian vein, positioned at the junction of the SVC and right atrium.

Physiologic determinants: CVP depends on venous return (blood volume, venous tone, and right heart function) and right ventricular compliance. Per Guyton's model, CVP is the pressure at which venous return and cardiac output curves intersect—it reflects the balance between mean systemic filling pressure (driving venous return) and cardiac function (right heart's ability to pump blood forward).

Elevated CVP is seen in: right heart failure, tricuspid stenosis/regurgitation, pericardial tamponade or constrictive pericarditis, volume overload, positive pressure ventilation, pulmonary hypertension/cor pulmonale, and superior vena cava obstruction. Clinically, elevated CVP manifests as jugular venous distension (JVD), hepatojugular reflux, and peripheral edema.

Decreased CVP is seen in: hypovolemia (hemorrhage, dehydration), and distributive shock states (early sepsis) due to venodilation and reduced venous return.

CVP waveform analysis (a, c, v waves; x, y descents) provides additional diagnostic information: absent 'a' wave in atrial fibrillation, cannon 'a' waves in AV dissociation (e.g., complete heart block, ventricular tachycardia), and large 'v' waves in tricuspid regurgitation.

Clinical use: CVP monitoring is used in critically ill patients to guide fluid resuscitation, though its reliability as a sole predictor of fluid responsiveness has been questioned in modern critical care literature (dynamic indices like pulse pressure variation are now often preferred). CVP is also relevant in the physical exam via jugular venous pressure (JVP) estimation, a key component of the cardiovascular exam for assessing volume status and right-sided heart failure.

High-yield exam correlations: CVP is a key component of Guyton curves relating venous return to cardiac output—understanding how changes in blood volume, venous tone, and cardiac contractility shift these curves is tested extensively on Step 1.