Hemolysis During Hemodialysis

Low-grade chronic hemolysis is common in uremia, as red blood cell life span is clearly decreased with reduced renal function. Using isotope red cell tagging, it has been shown that red cell life span averages about 1/2 to 1/3 of normal in uremia. In addition, uremic erythrocytes have been found to be less deformable and osmotically more fragile when compared to their normal counterparts. Transfusion of uremic erythrocytes into an individual with normal renal function will restore the life span of those cells to normal. On the other hand, normal erythrocytes transfused into a uremic individual will have shortened survival. In the past, chronic hemolysis in maintenance dialysis patients may have manifested as increased blood transfusion require-ments. However, these days such hemolysis probably more often presents itself as erythropoietin resistance (larger erythropoietin doses being required for a given therapeutic response). A variety of abnormalities (such as impairment of red cell enzymatic activities and reduced synthesis of Na+ - K+ pump units by uremic reticulocytes) have been suggested to be the causes for the heightened predisposition of uremic erythrocytes to hemolysis. Uncommonly, patients on dialysis can have severe (at times life-threatening) hemolysis. These patients fit into either of two categories, depending on whether hemolysis involves all or the majority of the patients being dialyzed under similar circum-stances in a given dialysis center or whether the hemolysis is patient specific. Hemolysis in the former is often the result of water-borne toxins, centralized dialysis equipment failure, or blood tubing defects—whereas in the latter it results from medication or possibly inadequate dialytic therapy. Use of constricted blood tubing systems and of hypo-osmolal or abnormally warm dialysate results in intravascular hemolysis, whereas drug-induced hemolysis is usually extravascular.