THE GAIN OF RED-CELLS FROM PREOPERATIVE HEMODILUTION EVALUATION OF BENEFIT USING A MATHEMATICAL-MODEL

To avoid tranfusions with homologous blood, surgical losses are routin ely replaced with a plasma substitute until a predetermined minimal al lowable haematocrit has been reached (intraoperative haemodilution, IH D). On the other hand, in preoperative haemodilution (PHD) part of the the blood volume is replaced with a cell-free fluid before surgery an d the operation starts at the minimum haematocrit level. The harvested blood is used to replace the surgical bleeding and raises the haemato crit. Thus, for a given minimum haematocrit and for the same surgical bleeding, PHD gives a higher final haematocrit than that obtained with IHD. This gain, defined as the red cell mass after PHD minus that aft er IHD, has been studied in a mathematical model, and the outcome of a wide range of degrees of PHD is presented. The general conclusion fro m the study is that the gain from PHD is minor if the surgical bleedin g is compensated with the harvested blood only. On the other hand, if after dilution the surgical bleeding is initially compensated by a pla sma substitute and the major part of the stored red cells are not infu sed until after successful haemostasis, more blood can be saved, justi fying PHD as a blood-saving method.