Objective: The study aimed to evaluate the effect of mild and moderate hemodilution during CPB on the neurocognitive dysfunction in patients undergoing coronary artery bypass grafting. 

Design: A randomized clinical study. 

Setting: Cardiac center. 

Patients: 186 patients scheduled for cardiac surgery with cardiopulmonary bypass. 

Intervention: The patients were classified into 2 groups (each = 93), Mild hemodilution group: The hematocrit value was maintained >25% by transfusion of packed-red blood cells plus hemofiltration during CPB. Moderate hemodilution group: the hematocrit value was maintained within the range of 21-25%.

 Measurements: The monitors included the hemofiltrated volume, number of transfused packed red blood cells, and the incidence of postoperative cognitive dysfunction. 

Main Results: The hemofiltrated volume during CPB was too much higher with mild hemodilution compared to the moderate hemodilution (p = 0.001). The number of the transfused packed red blood cells during CPB was higher with mild hemodilution compared to the moderate hemodilution (p = 0.001), but after CPB, the number of the transfused packed red blood cells was lower with the mild hemodilution group than the moderate hemodilution (p = 0.001). The incidence of total postoperative neurological complications was significantly lower with the mild hemodilution group than moderate hemodilution (p = 0.033). The incidence of neurocognitive dysfunction was significantly lower with mild hemodilution group than moderate hemodilution (p = 0.042). Conclusions: The mild hemodilution was associated with a significant decrease in the incidence of neurocognitive dysfunction compared to moderate hemodilution in patients undergoing coronary artery bypass grafting. Also, the transfused packed red blood cells increased during CPB and decreased after CPB with the mild hemodilution than moderate hemodilution.