Effect of red cell volume reduction on pulmonary blood flow in polycythemia of cyanotic congenital heart disease

Abstract

The acute effects of red cell volume reduction (erythropheresis) on pulmonary blood flow and pulmonary vascular resistance were measured in 16 patients with severe shunt-induced polycythemia. In subjects with D-transposition of the great arteries and no significant pulmonary stenosis (Group A) erythropheresis was associated with a decrease in pulmonary vascular resistance and an increase in pulmonary blood flow and in mixing between the systemic and pulmonary circulations. Systemic arterial saturation decreased slightly. By contrast, erythropheresis in patients with severe pulmonary stenosis or atresia and a ventricular septal defect (Group B) was associated with a decrease in pulmonary blood flow and left to right shunt and an increase in right to left shunt. These alterations resulted in a significant reduction in systemic arterial oxygen saturation despite relatively little change in effective pulmonary blood flow. The acute hemodynamic effects of packed red cell transfusion in five patients with D-transposition of the great arteries, no significant pulmonary stenosis and relative anemia were more variable. The observations in patients with shunt-induced polycythemia are probably related to a reduction in blood viscosity produced by a lowering of hematocrit concentration. The reduced viscosity decreases the impedance to flow in the systemic and pulmonary circulations. When pulmonary blood flow is largely derived from the systemic circuit, erythropheresis will diminish pulmonary flow and reduce systemic oxygen saturation. If the pulmonary blood flow is largely independent of the systemic circuit (as in D-transposition of the great arteries without pulmonary stenosis), an increase in total and effective pulmonary flow occurs.