What is Systemic Vascular Resistance (SVR)?

Systemic Vascular Resistance (SVR) represents the resistance to blood flow offered by all of the systemic vasculature, excluding the pulmonary circulation. It is a critical component of hemodynamic monitoring and helps clinicians understand the state of a patient's cardiovascular health, particularly in critical care settings.

The SVR Formula

To calculate SVR, we look at the pressure gradient across the systemic circulation divided by the flow rate. The standard formula used in this calculator is:

SVR = ((MAP - CVP) / CO) × 80

Where MAP is Mean Arterial Pressure, CVP is Central Venous Pressure, and CO is Cardiac Output. The constant 80 is used to convert the units from mmHg·min/L to dyn·s/cm&sup5;.

How to Use the SVR Calculator

Using this tool is straightforward. Follow these steps:

• Enter MAP: Input the Mean Arterial Pressure measured in mmHg.
• Enter CVP: Input the Central Venous Pressure in mmHg. If unavailable, clinicians sometimes use a default low value, though precise measurement is preferred.
• Enter Cardiac Output: Provide the CO in liters per minute (L/min).
• Interpret Results: A normal SVR range is typically between 800 and 1200 dyn·s/cm&sup5;.

Clinical Significance and FAQs

What does a high SVR mean? High SVR indicates vasoconstriction, which can occur in states like hypovolemic shock, cardiogenic shock, or hypothermia. The heart has to pump against higher resistance.

What does a low SVR mean? Low SVR indicates vasodilation, often seen in distributive shocks such as septic shock, anaphylaxis, or neurogenic shock.

Is SVR the same as blood pressure? No. While SVR contributes to blood pressure, blood pressure is a product of Cardiac Output and SVR. You can have high SVR with low blood pressure if the heart's output is sufficiently low.