When discussing shock, critical illness, and organ dysfunction, we often focus heavily on arterial circulation. Mean arterial pressure, cardiac output, and systemic vascular resistance dominate many bedside conversations. Yet many patients in the ICU suffer not from inadequate arterial flow, but from excessive venous pressure.
Venous congestion represents an increasingly recognized mechanism of organ dysfunction. Elevated venous pressures can impair renal function, worsen hepatic injury, reduce gastrointestinal perfusion, and contribute to fluid overload despite seemingly adequate blood pressure and cardiac output.
To understand venous congestion, it helps to remember that organ perfusion depends on a pressure gradient rather than an absolute pressure. Renal blood flow is determined by the difference between arterial inflow pressure and venous outflow pressure. When central venous pressure rises, the effective perfusion gradient decreases even if MAP remains unchanged.
Historically, clinicians often used CVP as a surrogate for volume status. Unfortunately, CVP performs poorly for predicting fluid responsiveness. However, CVP remains valuable as a marker of venous congestion.