WILLIAM R. CLARK AND
ZBYLUT J. TWARDOWSKI

Dirk De Wachter, PhD, of the University of Gent, Belgium, presented “Mechanical Limits to Blood Flow Through the Extracorporeal Circuit Dependent on the Size, Shape, and Length of Needle or Catheter, and the Blood Pump Characteristics.” The relationship between blood flow and hydraulic resistance is not linear, but is more appropriately expressed as an exponential function. The best pressure/flow relationship is found in devices with circular cross sections. High flow rates against high resistance may cause clinically significant hemolysis at various places in the circuit.

Zbylut J. Twardowski, MD, PhD, the University of Missouri, Columbia, Missouri, measured blood flow by ultrasound flowmeter and assessed hemolysis during a single routine dialysis in 100 patients. Before and after the hemodialysis session, blood was drawn for measurement of haptoglobin (HPT), hemoglobin (Hb), albumin (Alb), and lactate dehydrogenase (LDH). Mean HPT concentrations increased markedly less during hemodialysis than did concentrations of Alb, Hb, and LDH, indicating that some hemolysis was present in all dialyses. In dialyses with arterial chamber pressures more negative than –350, the median concentration of Alb increased significantly more than the median concentration of Hb, which indicates significantly more hemolysis in dialyses with pressures more negative than in those with less negative arterial chamber pressures. Whether this slightly increased hemolysis is of clinical significance is uncertain. Erythropoietin requirements were not significantly different in patients dialyzed with more and less negative arterial chamber pressures.