Background

To assess solely effects of red blood cell (RBC) components or efficacy of artificial oxygen carriers in relevant clinical models, it is necessary to induce severe normovolemic anemia. Since phlebotomy and volume replacement with crystalline fluids introduces additional variables such as platelet loss, loss of clotting factors and loss of oncotic pressure, we sought to establish severe anemia by selective removal of RBCs, using apheresis.

Methods

The method was established using three independent pools of ABO-identical buffy coats (BC pool) with a combined total volume of 1768ml (1115-1781) in a Spectra Optia BMP bag. This volume is equivalent for big animal model (sheep/pigs). Complete blood counts (CBC), especially haemoglobin (Hb) (median 8,7g/dl; range 8,2-10,9), provided a reasonable approximation of e.g. sheep blood (8-12g/dl). The Spectra Optia TEA with normal saline as replacement fluid was used for RBC depletion. To avoid a prefill, variables yielding a fictitious total blood volume of 2600ml were entered. 55% was entered as haematocrit of the replacement fluid. BC pools were processed with an inlet flow of 20-25ml/min, with manual mixing every five and CBC every 15 minutes

Results

Our targeted Hb of 4-6g/dl was reached in all runs after 45 minutes. We continued the run for a total of 60 minutes to ascertain the limits of the method. Hb dropped in a highly reproducible, near-linear fashion over time. As expected, given that true Hb in the patient is not supervised by Spectra Optia TEA, no alarms prevented the essentially limitless reduction of the Hb. With respect to blood volume, normovolaemia was preserved, as intended (99%; -27- -9ml). Platelet loss was considerable (43%; 42-60) and could not be reduced by entering a false-low Hb.

Conclusion

With the mentioned modifications and using crystalline replacement fluid, Spectra Optia TEA can be harnessed to reproducibly establish profound normovolemic anemia within an adequate period of time. The model experiments do not account for release of blood components from spleen that can occur in vital big animal models such as sheep or pigs. As a next step, we will seek to corroborate the method in vivo in a big animal model.

Offenlegung Interessenkonflikt:

There are no conflicts of interest to declare.