EFFECTS OF TOTAL HEMOGLOBIN AND HEMOGLOBIN-S CONCENTRATION ON CEREBRAL BLOOD-FLOW DURING TRANSFUSION THERAPY TO PREVENT STROKE IN SICKLE-CELL-DISEASE

Background The standard treatment of stroke in sickle cell disease is chronic transfusion to maintain the fraction of abnormal hemoglobin (h emoglobin S [HbS]) below 20%. Risks associated with such transfusion c an be reduced by allowing higher HbS levels, but the physiological con sequences of this modification are unknown. Cerebral blood flow is ele vated in sickle cell disease proportionate to the degree of anemia and is reduced by transfusion. We tested the effects of various HbS level s on cerebral blood flow during the course of transfusion therapy. Cas e Descriptions We monitored cerebral blood flow (by the Xe-133 inhalat ion method) in three patients whose chronic transfusion program was ch anged from a traditional regimen (HbS <20%) to a moderate one, allowin g HbS to rise to 45% to 50% between treatments. As expected, cerebral blood flow was higher with lower hemoglobin and higher HbS concentrati on. However, the HbS fraction appeared to exert a separate influence o n the hyperemia, independent of total hemoglobin concentration. Furthe rmore, cerebral blood flow was higher during the modified regimen, des pite equivalent anemia. Conclusions These results suggest caution in a dapting the modified transfusion regimen. Although HbS concentrations of 50% did not cause any frank neurological sequelae, the possible con sequences of the associated hyperemia over time are unknown. We conclu de that larger clinical and physiological studies of moderate transfus ion regimens (allowing higher concentration of HbS) are necessary befo re it can become standard therapy.