What is central venous pressure, its normal range in mm Hg, and how are elevated or decreased values interpreted clinically?

Central Venous Pressure: Definition, Normal Range, and Clinical Interpretation

Definition

Central venous pressure (CVP) represents the pressure within the right atrium or superior vena cava, reflecting right atrial end-diastolic pressure and serving as an estimate of right ventricular preload. 1 It is determined by the interaction between cardiac function and venous return. 2

Normal Range and Units

The normal CVP range is 3-8 cm H₂O (approximately 2-6 mmHg) in non-mechanically ventilated patients. 3 For mechanically ventilated patients or those with increased intra-abdominal pressure, the normal range is higher at 8-12 mmHg. 3

• CVP can be expressed in either millimeters of mercury (mmHg) or centimeters of water (cmH₂O), with a conversion rate of approximately 1 mmHg ≈ 1.36 cmH₂O 3
• The American Thoracic Society recommends using mmHg for reporting CVP values 3

Clinical Interpretation of CVP Values

Low CVP (<3 cm H₂O or <2 mmHg)

Low CVP typically indicates hypovolemia and inadequate circulating blood volume. 3

• In observational studies, 35.3% of patients with CVP readings <3 cm H₂O were classified as hypovolemic 3
• Eight out of 12 patients with CVP readings of zero or less presented in shock state 3
• Clinical action: Consider fluid resuscitation with crystalloids, starting with 30 mL/kg within the first 3 hours in septic patients 4

Normal CVP (3-8 cm H₂O or 2-6 mmHg)

Normal CVP suggests normovolemia and optimal hydration status. 3

• In non-ventilated patients, 47% had CVP readings of 3-10 cm H₂O and were considered normovolemic 3
• An optimal CVP range of 6-8 mmHg has been associated with minimal risk of acute kidney injury in cardiac surgery patients 3

Elevated CVP (≥10 mmHg)

Elevated CVP indicates either fluid overload, cardiac dysfunction, or increased intrathoracic pressure. 3 The clinical interpretation depends heavily on the underlying condition:

In Cardiogenic Shock:

• CVP >15 mmHg combined with cardiac index <2.2 L/min/m² and elevated systemic vascular resistance defines cardiogenic shock 5
• Pulmonary capillary wedge pressure >15 mmHg accompanies the elevated CVP, reflecting left ventricular failure 4, 5
• Clinical signs include pulmonary edema, jugular venous distension, cool extremities, and signs of organ hypoperfusion 5

In Organ Donor Management:

• Target CVP of 4-12 mmHg is recommended during aggressive hemodynamic management 4
• With pulmonary artery catheter guidance, maintain CVP 4-12 mmHg alongside pulmonary capillary wedge pressure 8-12 mmHg 4

In Septic Shock:

• The Surviving Sepsis Campaign previously recommended CVP targets of 8-12 mmHg in non-ventilated patients 3
• However, the use of CVP alone to guide fluid resuscitation can no longer be justified because CVP within a relatively normal range (8-12 mmHg) has limited ability to predict response to fluid challenge 4

Critical Limitations of CVP Measurement

Static CVP measurements have poor predictive value for fluid responsiveness, with a positive predictive value of only approximately 50% when CVP is less than 8 mmHg. 4, 3

• Dynamic measures (passive leg raises, pulse pressure variation, stroke volume variation) demonstrate superior diagnostic accuracy for predicting fluid responsiveness 4
• Pulse pressure variation in septic patients showed sensitivity of 0.72 and specificity of 0.91 for predicting fluid responsiveness 4
• CVP should not be used as the sole parameter to guide fluid therapy but rather in conjunction with other clinical parameters including heart rate, blood pressure, arterial oxygen saturation, respiratory rate, temperature, urine output, and echocardiography 4, 3

Hemodynamic Differentiation Using CVP

CVP helps differentiate shock types when combined with other hemodynamic parameters:

• Hypovolemic shock: Decreased CVP, decreased cardiac output, increased systemic vascular resistance 5
• Cardiogenic shock: Elevated CVP (>15 mmHg), decreased cardiac index (<2.2 L/min/m²), elevated systemic vascular resistance, elevated pulmonary capillary wedge pressure 4, 5
• Distributive shock: Normal or decreased CVP, normal or increased cardiac output, decreased systemic vascular resistance 5
• Obstructive shock: Elevated CVP with specific patterns depending on the obstruction 5

Special Considerations

In Acute Myocardial Infarction with Cardiogenic Shock:

• CVP >10 mmHg combined with pulmonary capillary wedge pressure >0.63 mmHg and pulmonary artery pulsatility index <2.0 may identify right ventricular dysfunction, which complicates 38% of cardiogenic shock cases 4

In Restrictive Cardiomyopathy:

• Higher CVP targets may be necessary because stiff, non-compliant ventricles require elevated filling pressures to achieve adequate ventricular filling 3
• Even with restrictive physiology, excessive fluid administration can cause right ventricular overdistension and paradoxically worsen cardiac output 3