Mechanisms of Plasma Hemoglobin Clearance after Acute Hemolysis

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Abstract
Mechanisms of plasma hemoglobin clearance after acute hemolytic episodes were studied in a group of patients having open-heart surgery employing extracorporeal circulation. These studies were directed toward hemoglobin-haptoglobin relationships and renal hemoglobin excretion. Clearance rates of hemoglobin bound to hapto-globin and free, or unbound, hemoglobin were determined. Free hemo-globin was removed from the plasma at a more rapid rate than that portion bound to haptoblogin. Hemoglobin was not excreted in the urine until the plasma hemoglobin level rose significantly above the serum haptoglobin level, rather than at the first appearance of free hemoglobin. Renal excretion of hemoglobin ceased before the plasma was cleared of free hemoglobin and while the appreciable levels were still present. Only a small percentage of the free hemoglobin theoretically available for renal excretion was actually excreted in the urine, suggesting that the kidneys are not a primary factor in plasma hemoglobin clearance. The major portion of free hemoglobin was removed from the plasma by mechanisms as yet not defined, but presumably by direct tissue deposition.