Aggressive Zero Balance Ultrafiltration on CPB in Patients with Renal Failure May Cause Cerebral Edema: A Theoretical Analysis

Hemofiltration during cardiopulmonary bypass (CPB) is used to correct hemodilution and correct electrolyte imbalance of patients with renal failure (1). Hemofiltration on or off CPB in the setting of renal failure can result in osmotic changes caused by rapid changes in serum urea concentrations. Large osmotic changes in extracellular compartments can potentially lead to cerebral edema. Cerebral edema is assumed to be the cause of dialysis disequilibrium syndrome characterized by headache, disorientation, nausea, seizures, and coma (2). Animal studies have shown that the resulting cerebral edema could be caused by the “reverse urea effect,” in which brain urea remains relatively high despite rapid decrease in plasma urea (3). We therefore set out to analyze the potential effect of aggressive filtration during CPB on brain volume.