[Evaluation of the tolerance to hemorrhagic shock--comparison between hemodilution and non-hemodilution]

We induced various degrees of bleedings in adult mongrel dogs to determine their tolerance to bleedings. The dogs were divided into two groups: the hemodilution group (Group A: Hct 11.1 +/- 1.9%) and the non-hemodilution group (Group B: Hct 36.8 +/- 6.6%). The Group A tended to show higher tolerance to bleedings than the Group B, although the difference was not significant. Throughout the period of increasing degrees of bleedings, MAP remained higher in Group B than in Group A, but CI was higher in Group A than Group B. DO2I was kept higher in Group B than in Group A. Both PaO2 and PaCO2 showed no difference between the two groups. The results of our study indicate that hemodilution group tends to be more tolerant to bleeding than non-hemodilution group. The reason is probably that under hemodilution the oxygen delivery is maintained through an increase in cardiac output in the presence of decreased arterial oxygen content. In addition, it is considered that the safety is obtained through various factors such as preferential blood distribution to important organs (in particular to the myocardium), more efficient extraction of oxygen from the blood, and the decreased work load resulting from a reduced blood viscosity.