OPTIMAL TIMING OF HEMODILUTION FOR BRAIN PROTECTION IN A CANINE MODELOF FOCAL CEREBRAL-ISCHEMIA

Background and Purpose Hemodilution is known to ameliorate the effects of focal ischemia when used shortly after cerebral arterial occlusion ; however, it remains to be proved whether hemodilution will be effect ive when used at more clinically relevant times, ie, with some delay b etween the onset of ischemia and initiation of therapy. Methods Thirty -two dogs were selected for inclusion in this study. Cerebral infarcti on was induced by permanent occlusion of the middle cerebral and the a zygos anterior cerebral arteries. The animals were allocated to 1 of 4 groups of eight animals each: arterial occlusion without hemodilution (group 1); hemodilution immediately after occlusion (group 2); hemodi lution 3 hours after occlusion (group 3); and hemodilution 6 hours aft er occlusion (group 4). Isovolemic hemodilution to a hematocrit of 30% was performed. The animals were killed 6 days after induction of isch emia, and the infarct size was determined. Results Groups 2 and 3 show ed significant reduction of infarct size (P<.0001) when compared with group 1. The neurological grade of group 3 on postoperative days 4, 5, and 6 was significantly better than those of groups 1 and 4 (P<.01). Group 3 showed a significant increase in the incidence of hemorrhagic infarction when compared with groups 1 and 2 (P<0.01). Conclusions The current study indicates that hemodilution administered as much as 3 h ours after ischemia is effective in reducing infarct size and improvin g neurological status. When administered 6 hours after ischemia, hemod ilution is not helpful and may be harmful.