Benefits of isovolemic hemodilution red cell exchange: Real or imagined?

Isovolemic hemodilution red cell exchange (IHD-RCE) (as compared to standard, or STD-RCE) may: reduce per-procedure RBC use, result in a lower fraction of cells remaining (FCR), and provide an "iron unloading" benefit. We review the published literature to explore whether these benefits have been realized in real-world settings.

A literature search was conducted in PubMed, Embase, EBSCOhost, and Cochrane Library. Additional studies were identified through bibliography review. To be included, studies required STD-RCE versus IHD-RCE comparison groups. Data, including RBC utilization, actual FCR, ferritin levels, pre-hemoglobin S% (HbS%), and procedure intervals were extracted and analyzed using descriptive statistics.

The initial search and bibliography review yielded 70 studies; 48 were excluded for not meeting inclusion criteria; of the remainder, 3 reports met full inclusion criteria and were retained for data extraction. Compared to STD-RCE, IHD-RCE reliably reduced red cell requirements, with reduction (in mL/mL Total Blood Volume) from 0.55 (0.42-0.66) to 0.49 (0.34-0.54), among 15 patients (p = 0.02); and (in mL/kg) from 39.5 ± 4.6 to 35.5 ± 4.1 (p < 0.001) in another 20 patients. While actual FCR was lower than programmed FCR with both STD-RBCx and IHD-RBCx, the magnitude of this difference was not significantly different (n = 15). Among 26 patients for whom ferritin levels were reported, a clear reduction was not observed. Furthermore, no clear safety signals were observed.

Conversion to IHD-RCE appears safe and reduces per-procedure RBC utilization by approximately 1 unit. IHD-RCE did not demonstrate a clear iron-unloading benefit over STD-RCE.