Effects of blood viscosity on renal function during cardiopulmonary bypass - investigations in infants and experimental setting in pig kidneys

Objectives

Acute renal failure (ARF) is a common complication following open heart surgery especially in infants. Effects of blood viscosity on renal function are well known, but have not been investigated in cardiopulmonary bypass (CPS) as yet.

Material and methods

We investigated blood viscosity and different markers of glomerular and tubular renal function in a group of 37 infants below 18 month of age, receiving CPS surgery for different diagnoses.

In an experimental setting, we investigated 28 isolated pig-kidneys with different hematocrits in an autologous blood perfused model.

Results

In infants, creatinine clearance decreased and urinary excretion of albumin and β-NAG increased during the aortic cross clamp time (AT) and during the first hours following operation, indicating moderate glomerular and tubular damage. During AT, blood was hemodiluted to a hemoglobin of 8.4 ± 0.4 g/dl. Thus, blood viscosity during AT and hypothermia was slightly below pre-CPB values. Lower blood viscosity was related to less renal damage (P < 0.01).

In isolated pig-kidneys, group I (n = 14) was perfused with a hemoglobin of 10.2 ± 0.3 g/dl and group II (n = 14) was hemodiluted to 6.5 ± 0.9 g/dl. Group II kidneys showed lower vascular resistance, elevated creatinine clearance, elevated oxygen consumption and elevated sodium reabsorption (P < 0.05).

Conclusions

Reducing blood viscosity below physiological values improves tubular as well as glomerular function under CPB conditions. Thus we hold hemodilution to be an appropriate method for optimizing CPB procedures.