Haemodilution improves organ function during normothermic cardiopulmonary bypass: investigations in isolated perfused...

We investigated the effects of haemodilution on kidney function during normothermic cardiopulmonary bypass (CPB) by performing in vitro haemoperfusion of pig kidneys for 90 min after cold preservation. We compared two groups (n = 14 each) with respect to rheologic and haemodynamic parameters and glomerular and tubular function. Group 1 was perfused at a haematocrit of 0.33 +/- 0.01, group 2 at 0.21 +/- 0.01. Blood flow was adjusted according to blood pressure. Blood viscosity and vascular resistance were reduced in group 2. Comparison of group 1 versus group 2 revealed a metabolic rate of oxygen 3.4 +/- 1.7 versus 4.3 +/- 1.8 ml/min/100 g, sodium transport 1.2 +/- 1.2 versus 1.8 +/- 1.2 mmol/min/100 g, and creatinine clearance 9.9 +/- 9.1 versus 15.6 +/- 11.9 ml/min/100 g, p < 0.05. We conclude that haemodilution leads to an overproportional decrease in blood viscosity and improves the properties of flow and kidney function. In the ongoing discussion about the optimal extent of haemodilution in CPB, the importance of viscosity and blood flow should be further emphasized.