The association of hemodilution and transfusion of red blood cells with biochemical markers of splanchnic and renal injury during cardiopulmonary bypass.

Hemodilution is the main cause of a low hematocrit concentration during cardiopulmonary bypass. This low hematocrit may be insufficient for optimal tissue oxygen delivery and often results in packed cell transfusion. Our objective in this study was to find a relationship between intraoperative hematocrit and allogeneic blood transfusion on release of postoperative injury markers from the kidneys and the splanchnic area. Fifty consecutive patients undergoing coronary artery bypass grafting with cardiopulmonary bypass were included. Systemic tissue hypoxia was assessed by lactate concentrations. Kidney and splanchnic ischemia were assessed by the measurement of N-acetyl-beta-D-glucosaminidase (NAG) and intestinal fatty acid binding protein (IFABP) in urine. Patients were retrospectively placed into groups according to their lowest hematocrit concentration on bypass (<24% or >or=24%). The intraoperative lactate and the postoperative NAG and IFABP concentrations were higher in the low hematocrit group (<24%) than in the high hematocrit group (>or=24%; P < 0.05). Low hematocrit correlated with higher lactate concentrations (R(2) = 0.150, P < 0.01) and with higher NAG concentrations (R(2) = 0.138, P < 0.01) and IFABP concentrations (R(2) = 0.107, P < 0.01) postoperatively. Transfusion of packed cells during cardiopulmonary bypass correlated with higher lactate (R(2) = 0.089, P < 0.05), NAG (R(2) = 0.431, P < 0.01), and IFABP concentrations (R(2) = 0.189, P < 0.01). The results support the concept that hemodilution below an intraoperative hematocrit of 24% and consequently transfusion of red blood cells is related to release of injury markers of the kidneys and splanchnic area.