Effects of different degrees of acute normovolemic hemodtiution on serum S-100B protein concentration and cerebral oxygen metabolism in rabbits

Abstract

Objective To investigate the effects of different degrees of acute normovolemic hemodilution (ANH) with 6% HES 20010.5 on serum S-100B protein concentration and cerebral oxygen metabolism at 37℃ in rabbits.Methods Thirty-two adult rabbits weighing 2.0-2.5 kg were randomly assigned into 4 groups (n = 8each) : Ⅰ control group underwent no ANH and Ⅱ , Ⅲ , Ⅳ ANH group underwent ANH with hematocrit (Hct)reduced to 24%, 18% and 12% respectively. The animals were anesthetized with iv 20% urethane 5 ml/kg,tracheostomized and mechanically ventilated (VT = 15 ml/kg, RR = 30 bpm). The body temperature was maintained at 37℃. Left carotid artery and jugular vein were cannulated for BP monitoring, blood gas analysis and blood sampling. Right jugular vein was cannulated for CVP monitoring. Left femoral artery and vein were cannulated for hemodilution. Blood withdrawn from femoral artery was simultaneously replaced by iv infusion of equal volume of HES (200/0.5) until the target Hct was achieved. Hemodynamics parameters, were recorded and blood gases were analyzed and serum S-100B protein concentration and cerebral O2 metabolic rate (CERO2) were determined before (baseline) and at 2, 4 and 8 h after ANH. Brain water content was measured by wet/dry brain weight ratio. Results There were no significant differences in serum S-100B protein concentration, CERO2 and pH value between group Ⅰ and group Ⅱ (Hct 24%). Serum S-100B protein concentration and CERO2 were significantly increased at 8 h after ANH as compared with the baseline before ANH in group Ⅰ (Her 18%). Serun S-100B protein concentration and CERO2 were significantly increased at 2, 4 and 8 h after ANH as compared with the baseline before ANH in group Ⅳ (Hct 12%). There was no significant difference in brain water content among the 4 groups. Conclusion ANH does not affect cerebral O2 metabolic when Hct is reduced to 24%. CERO2 can not be sustained and ischemic cerebral injury may occur when Hct is reduced to≤18%. Key words: Hemodilution ; S100 proteins; Brain ; Oxygen consumption