Revisiting the benefits of isovolemic hemodilution red cell exchange for sickle cell disease.

Background: Isovolemic hemodilution red cell exchange (IHD-RCE) is a modified form of the standard red cell exchange (STD-RCE), intended to reduce red cell requirements in patients with sickle cell disease (SCD). This retrospective crossover analysis of nine patients aims to add to the limited existing literature on IHD-RCE and address the equipoise regarding whether the benefits of (a) decreased RBC usage per exchange and (b) increased interprocedure interval (via lower fraction of cells remaining, FCR) can be observed at the same time, in the same patient.

Methods: At a single center, we identified 37 patients with SCD undergoing chronic RCE between 2014 and 2021. We excluded those patients who did not have at least six consecutive procedures of each type (STD- and IHD-RCE), arriving at nine patients for analysis.

Results: When using greater decreases in hematocrit than previously published, we did not find that IHD-RCE resulted in any clinically apparent adverse events. We did find greater decreases in diastolic blood pressure and increases in heart rate in some patients, as compared to STD-RCE. After correcting for total blood volume, seven of the nine patients had significantly reduced red cell requirements with each IHD-RCE. Because the pattern of achieving a lower FCR than programmed was seen to an equal extent with both IHD-RCE and STD-RCE, none of the nine patients showed any statistical difference in actual FCR between procedure types.

Discussion: Our data do not support the observation of both IHD-RCE benefits, decreased red cell usage per exchange and lower FCR/increased interprocedure interval, simultaneously.