Abstracts of Posters Presented at the International Anesthesia Research Society; 72nd Clinical and Scientific Congress; Orlando, FL; March 7-11, 1998: Cardiovascular Anesthesia
INTRODUCTION: Acute normovolemic hemodilution (ANH) has been advocated as a simpler, less expensive alternative or supplement to autologous blood donation . However, studies of its efficacy have produced conflicting conclusions [2,3], partly because of differing values for the large number of parameters involved. In this work we develop a simple, general method to evaluate whether ANH is indicated and, if so, the maximum blood loss which may be tolerated prior to transfusion of allogeneic blood.
METHOD: The basic differential equations which govern ANH are manipulated to obtain general formulae describing the efficacy of ANH. We assume that normovolemia is maintained at all times and that the in vivo Hb concentration, [Hb], never drops below a specified target value, cT. We find that the main variables are ratios of clinically relevant parameters (for example, the ratio of the blood volume lost during surgery to the initial blood volume, VL/V0).
RESULTS: The following graph shows when ANH is indicated, in terms of two ratios: VL/V0 (described above) and cT/c0, the ratio of the target [Hb] to the initial [Hb]. (Figure 1)
In Region 1 ANH is not necessary because [Hb] does not drop below the target value. In Region 3 ANH reduces, but does not eliminate, the need for allogeneic transfusion. In Region 2 ANH can be used to completely avoid allogeneic blood transfusion. For example: for cT/c0 = 50%, ANH allows a maximum surgical blood volume loss which is equal to the initial blood volume.
CONCLUSION: There exists a useful range of parameters for which ANH can significantly reduce or even completely eliminate the need for allogeneic blood transfusion.
1. New England J. Med. 332:740-742, 1995.
2. Transfusion 35:37-41, 1995.
3. Transfusion 34:176-179, 1994.