Sickle Cell RBC Exchange Volume

Why Use

Sickle cell disease is associated with a number of complications, including pain crises, acute chest syndrome, and stroke. Automated RBC exchange is an effective therapeutic modality both in the acute treatment of severe sickle cell-related complications and in long-term maintenance. Calculating the volume of donor RBCs necessary to achieve appropriate reduction in HbS% is useful when ordering blood for RBC exchange procedures.

When to Use

Patients with sickle cell disease complications requiring RBC exchange.

Formula

Pearls / Pitfalls

Due to frequent exposures to donor RBCs, patients with sickle cell disease are at high risk for developing RBC alloimmunization and many centers require some level of antigen matching. In patients necessitating RBC exchange for an acute complication, if the pre-exchange percent hemoglobin S (HbS%) is unavailable, assuming that it is equal to 100% can be a conservative measure. Transfused blood for sickle cell patients should be antigen negative for any patient RBC alloantibodies, crossmatch compatible, and sickle negative. This calculation is intended to produce the same hematocrit post-procedure as pre-procedure. Apheresis instruments have on-board calculators to adjust hematocrit according to user-entered preferences, which may necessitate adjustments to RBC replacement volume.

Advice

The calculated volume of replacement RBCs may be divided by 350 mL to approximate the number of RBC units to order. Adjustments to the patient’s hematocrit may require alterations to these calculations.