How does CPB influence postoperative renal function risk?

• A. It improves renal perfusion in most patients.
• B. It reduces risk of acute kidney injury.
• C. Hemodynamics and hemolysis can affect renal perfusion; monitor urine output and creatinine.
• D. It has no impact on kidney function.

Answer: (C)

The main concept is that cardiopulmonary bypass can alter kidney perfusion and increase the risk of postoperative kidney injury through a combination of hemodynamic changes and hemolysis. On bypass, perfusion pressures and flow can be variable, and nonpulsatile flow plus the systemic inflammatory response can reduce renal blood flow or cause periods of relative ischemia. At the same time, contact with the bypass circuit can cause hemolysis, releasing free hemoglobin that is nephrotoxic and can promote vasoconstriction and tubular injury. These factors together raise the risk of acute kidney injury after surgery.

That’s why monitoring urine output and creatinine is important: they provide real-time and functional insight into renal perfusion and function, helping clinicians detect emerging renal compromise and adjust management—such as pump flow, blood pressure targets, hematocrit levels, and fluid balance—to protect the kidneys.

The other statements aren’t correct because CPB does not reliably improve renal perfusion in most patients, nor does it inherently reduce the risk of AKI; it can contribute to kidney injury. Saying it has no impact on kidney function also ignores the well-documented renal risks associated with bypass.