Hemorheology and renal function during cardiopulmonary bypass in infants

Background. Acute renal failure is an occasional complication after cardiop ulmonary bypass in infants. Whereas it is well known that postoperative hem odynamics inflict acute renal failure, the influence of extracorporeal circ ulation on the kidney is less clear. Moreover, changes in blood viscosity o ccur during and after surgery, which may influence renal dysfunction. For t his reason, we investigated the impact of blood viscosity on renal function during cardiopulmonary bypass. Methods: In 34 patients weighting less than 10 kg, we performed repeated analysis of urine, blood, and plasma viscosit y. Results: Polyuria and proteinuria that appeared during cardiopulmonary b ypass indicated an elevated transglomerular filtration gradient, which reco vered within 24 hours. The appearance of N-acetyl-beta -D-glucosaminidase i n the urine, and elevated excretion of sodium, were additionally indicative of mild tubular damage. Elevation of blood viscosity during hypothermic pe rfusion showed a statistical correlation with proteinuria and N-acetyl-beta -D-glucosaminidaseuria. With hypothermia, the relation of blood viscosity to plasma viscosity became stronger, while the relation to the hematocrit d ecreased compared to normothermia. Conclusions: During cardiopulmonary bypa ss perfusion, the kidney can be stressed by proteinuria and mild tubular da mage. Our data provide evidence that the kidneys can be protected by improv ed blood viscosity during cardioplegia, but this needs confirmation in a pr ospective interventional study.