Acute reduction in red cell volume (RCV) without significant alterations of blood volume in 22 patients with severe polycythemia secondary to cyanotic congenital heart disease resulted in a decrease in peripheral vascular resistance and an increase in stroke volume, systemic blood flow (SBF), and systemic oxygen transport. These changes are probably related to the decreased blood viscosity and yield shear stress associated with lower red cell concentrations. Hypervolemia in hypoxic polycythemia should be maintained in order to sustain an adequate SBF. In contrast to acute phlebotomy which may be expected to decrease blood oxygen content and SBF, the replacement of whole blood with plasma or 5% albumin is shown to result in an increased systemic blood flow and oxygen delivery.

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