Although the efficacy of hydroxyethyl starch (HES) as a cryoprotectant for human red blood cells (HRBC) was demonstrated in 1967, no clinical application has evolved so far. In contrast to glycerol, which has been widely used for this purpose, HES offers the advantage of being nontoxic if administered intravenously. Being also a plasma substitute, HES in combination with HRBC can normalize blood volume as well as oxygen transport in the case of extended blood loss. This may be of importance for autologous blood supply for elective surgery and for disaster treatment plans. For a volume of 40 ml, the optimal combination of important parameters [e.g. cooling rate 200-250 K/min, warming rate 400 K/min, hematocrit 40%, HES concentration 12% (w/w)] has led to a survival after thawing in terms of saline stability of 93 +/- 1% (n = 10). Additionally, the age prior to cryopreservation (0-3 days) had an influence on postthaw survival, but at least 90% survival can be obtained if the samples are washed 3-5 times before freezing.
