What is a normal systemic vascular resistance (SVR)?

Normal Systemic Vascular Resistance Values

The normal range for systemic vascular resistance (SVR) is 800-1200 dynes·sec·cm⁻⁵, with values below 800 dynes·sec·cm⁻⁵ considered low and values above 1200 dynes·sec·cm⁻⁵ considered elevated. 1, 2

Understanding Systemic Vascular Resistance

SVR represents the resistance to blood flow offered by the systemic vasculature, excluding the pulmonary circulation. It is primarily determined by:

• Arteriolar tone
• Blood viscosity
• Vascular capacitance

The formula for calculating SVR is:

SVR = (Mean Arterial Pressure - Central Venous Pressure) / Cardiac Output

With units expressed as dynes·sec·cm⁻⁵ 2

Clinical Significance of SVR Values

Low SVR (<800 dynes·sec·cm⁻⁵)

• Associated with distributive shock states
• May be seen in:
  • Sepsis/septic shock
  • Anaphylaxis
  • Neurogenic shock
  • Post-cardiopulmonary bypass (seen in approximately 44% of patients) 3
• Extremely low values (<450 dynes·sec·cm⁻⁵) correlate with significantly higher mortality regardless of etiology 4
• Requires vasopressor therapy to restore vascular tone

Normal SVR (800-1200 dynes·sec·cm⁻⁵)

• Represents optimal vascular tone for adequate tissue perfusion
• Target range for hemodynamic management in critically ill patients 1

High SVR (>1200 dynes·sec·cm⁻⁵)

• Indicates increased afterload
• May be seen in:
  • Hypertensive crisis
  • Cardiogenic shock
  • Heart failure
  • Vasopressor excess
• May require vasodilator therapy to reduce afterload

Measurement Considerations

When measuring SVR in clinical practice:

1. SVR can be calculated using a pulmonary artery catheter that measures cardiac output directly
2. Central venous pressure (CVP) measurement has minimal impact on SVR calculation due to its narrow clinical range (5-15 mmHg) compared to mean arterial pressure (60-120 mmHg) 5
3. For practical purposes, using a fixed CVP value of 10 mmHg provides reasonable accuracy in SVR estimation when actual CVP measurement is unavailable 5
4. Non-invasive methods using finger photoplethysmography are being developed but are not yet standard of care 6, 7

Clinical Applications

SVR monitoring is particularly valuable in:

• Shock states to guide vasopressor or vasodilator therapy
• Post-cardiopulmonary bypass patients
• Heart failure management
• Critically ill patients requiring hemodynamic optimization

In cardiac donor management, maintaining SVR between 800-1200 dynes·sec·cm⁻⁵ is part of the recommended protocol for optimizing cardiac function before organ recovery 1.