Limit Values Of Acute Blood Loss For Secondary Brain Injury In Rats Under Basic Life Support

Objective To explore the influence of acute hemorrhagic anemia on the changes of brain spatial learning memory,cerebrospinal S100 beta proteins(S100?)and matrix metalloproteinases 9(MMP-9)in rats under basic life support,and to learn the limit values of acute blood loss for brain injury in rats.Methods 60 Wistar rats were randomly assigned into 5 groups(n=12): G0(control group),G2(20% blood-loss),G4(40% blood-loss),G6(60% blood-loss)and G8(80% blood-loss).Each group was divided into two subgroups according to the postoperative recovery time of 12 or 24 hours.Tracheal intubation and mechanical ventilation was administrated to each rat.The carotid artery and femoral vein was cannulated for monitoring average arterial pressure(MAP),heart rate(HR)and liquid transfusion.After the behavioral experiment,blood samples were taken immediately for blood gas analysis.Escape latent period(ELP)in water maze test was measured at 12 and 24 hours postoperatively.At the end of the test,0.1ml cerebrospinal fluid was taken for the measurement of contents of S100 beta and MMP-9.Results(1)At the end of the recovery,the MAP of G4 group was significantly lower and the HR was higher than the G0 group(P<0.05).Compared to G6 group,MAP in G8 group was significantly decreased and HR was increased(P<0.05).However,no significant difference exists in MAP or HR between group G0 and G2 before and after bloodletting.(2)The hemoglobin(Hb)and arterial oxygen content(CaO2)of G2 group was significantly lower and the HR was higher than the G0 group(P<0.05).Compared to G2 group,Hb and CaO2 in G4 group was significantly decreased(P<0.05).The contents of Hb and CaO2 in group G6 were increased significantly when compared to group G4(P < 0.05)..(3)Compared to the group G0,the contents of S100? or MMP-9 in group G2 was increased and the differences were significant(P<0.05).The contents of S100? or MMP-9 in group G4 were increased significantly when compared to group G2(P<0.05).Compared to the G4 group,the contents of S100? or MMP-9 in G6 group were significantly increased(P<0.05).(4)There was no significant difference in ELP between G2 and G0 group.Compared to G2 group,ELP in G4 group was significantly prolonged(P<0.05).ELP in G6 group was significantly prolonged(P<0.05)compared to G4 group.(5)All rats in group G0,G2 and G4 survived till the end of study,and the survival rate was 100%.Five rats died in group G6 within 24 hours and the survival rate was 58.3%;all rats in group G8 died within 12 hours,and the survival rate was 0%.Conclusion 20% volume of acute blood-loss for rats cannot lead to secondary brain function injury.40% volume of acute blood-loss leads to the deterioration of spatial learning and memory skill and the impairment of blood-brain barrier if this level of anemia lasts more than 12 hours and persisted after 24 hours on this occasion.The impairment will be aggravated if the 60% volume of acute blood-loss occurs,which can significantly reduce the 24-hour survival rate in rats.80% volume of blood-loss leads to the damage to an irreversible extent and the rats could not survive for more than 12 hours at this level of anemia.