Systemic Vascular Resistance (SVR) is a fundamental hemodynamic parameter used in the ICU to differentiate the specific type of shock a patient is experiencing and to tailor precise pharmacological therapies.
The Hemodynamic Triad
Blood pressure is determined by three things: how full the 'tank' is (fluid volume/CVP), how strong the 'pump' is (Cardiac Output), and how tight the 'pipes' are (Systemic Vascular Resistance).
If a patient is hypotensive, you must know which of the three is failing.
Differentiating Shock
- Cardiogenic Shock: The heart is failing (Low CO). The body compensates by clamping the pipes. Result: High SVR.
- Hypovolemic Shock: The tank is empty (Low CVP). The body compensates by clamping the pipes. Result: High SVR.
- Distributive Shock (Sepsis/Anaphylaxis): The pipes are paralyzed and open wide. Result: Low SVR.
SVR = [80 × (MAP - CVP)] / Cardiac Output
By calculating the SVR via a pulmonary artery catheter or advanced arterial line analysis, the intensivist knows whether the patient needs IV fluids, inotropic drugs to squeeze the heart, or vasopressors to squeeze the pipes.