Planning an exchange transfusion in patients with sickle cell syndromes.

Partial exchange transfusions are performed in sickle cell patients for a variety of reasons. An algorithm to plan a nonautomated exchange in patients with sickle cell syndromes was developed and validated by a study of 40 such procedures. Formulas that can be used to explore alternatives, by assessing at any point during the exchange the current concentration of sickleable cells and the hematocrit, were devised: a computer program in BASIC is available for maximum versatility. The two most important determinants of the exchange are the patient's initial hematocrit and the desired final concentration of sickleable cells; the rate and type of exchange (continuous or discontinuous) are not important. The final hematocrit depends on the type of blood product used. An exchange can be performed with packed red blood cells (PRBC), whole blood (or its equivalent, PRBC reconstituted with albumin), or it can be started with PRBC and continued with whole blood. Whole blood decreases the concentration of sickeleable cells rapidly and increases the hematocrit slowly; it does not markedly increase the viscosity. PRBCs decrease the concentration of sickleable cells more slowly and increase the hematocrit faster; thus, they may increase the blood viscosity to dangerous levels.