Effects Of Ventilation With Different Oxygen Concentration On Oxygen Metabolism, SOD And MDA During Acute Normovolemic Hemodilution

Objective:We investigated the effects of different oxygen concentration on the oxygen metabolism,superoxide dismustase(SOD)and malonydialdehyde(MDA)during acute normovolemic hemodilution,in order to select the proper oxygen concentration.Method:Thirty ASAâ… orâ…¡patients of either sex aged 18-65 year undergoing internal fixation surgery of vertebrae were included in the study. According to oxygen concentration of ventilation,patients were randomly divided into three groups:35%FiO₂(G35%),50%FiO₂(G50%),and100% FiO₂(G100%),n=10.Blood was withdrawn from radial artery after induction of anesthesia,and was simultaneously replaced with 6%hetastarch(HES 130/0.4)in a one to one ratio in all groups.The target Hct was 30%.The volum of blood removed(ml)=body weight(kg)×70×(preop Hct-targetHct)/0.5×(preop Hct+targetHct). Blood samples were colleted from radial artery and central vein at different time points including immediately before ANH(T₀),30 min and 1 h after ANH(T_1,2),immediately before reinfusion(T₃),1 h after reinfusion(T₄),blood gases were measured and recorded.HR,CVP,MAP were also recorded at above five time points.The central vein blood samples were collected and used for measuring MDA level and SOD activities.When Hct was less than 25%,homogous blood would be reinfused and allogeneic blood transfusion should be considerated according to the condition. Result:Hct and Hb in all groups decreased significantly to the target extent after ANH at T₁,reached the lowest point(Hct25%)at T₃(P＜0.05). Compared with T₀,C_aO₂,C_vO₂ decreased while ERO₂ increased generally in all groups,S_aO₂ increased firstly at timepoint "T₁,T₂"(P＞0.05),then declineded significantly at timepoint "T₃"(P＜0.05),while the ABL varied contrarily,declineded firstly at timepoint "T₁,T₂"(P＜0.05)and increased at timepoint "T₃"(P＜0.05),the Variables above changed greatly at timepoint "T₃",and the differences were significant among groups(P＜0.05),with the change of G35%greatest,these Variables improved after reinfusion.During the whole hemidilution,all these variables changed among the normal or were close to the normal,excluding the ABL of G35%at timepoint "T₃" (2.35±0.42nmol/L),however there was no obvious hypoxia.P_aO₂ and P_vO₂ in all groups increased accordingly as the inhaled oxygen concentration increased,and the differences among groups were sigifincant(P＜0.05),there was no siginfincant differernce of P_aO₂ from T₁ to T₄ in every group,P_vO₂ significantly decreased at T₃ compared with T₂ in all groups,Physically dissolved oxygen and the contributions of Physically dissolved oxygen to C_aO₂ changed similar to P_aO₂,chemically bounded oxygen in all groups were not different siginificantly at corresponding timepoint,but compared with T₀., decrased significantly at T₁～T₄.There were no statistical significances of SOD and MDA at T₀(P＞0.05),the activity of SOD decreased gradually while the MDA increased gradually on the contrary.The activity of SOD decreased significantly beginning from T₃ of G35%and T₁ of G50%and G100%,the differences among groups were signifincant,and the change of G100%was the greastest,the differences among groups and within the group of MDA were similar to the changes of SOD.Conclusions:Ventilation with 35%O₂ can basically provide demands of oxygen metabolism with stable haemodynamics,and no obvious hypoxia is indicated during moderate normovolemic hemodilution (Hct25%),compared with 35%O₂,Ventilation with 50%O₂ or more may have superiority for advanced hemodilution.With time and concentration of inhaled oxygen increasing,the activity of SOD is generally inclined while the concentration of MDA increased within short time(no more than 5h),among three groups,the effects on SOD and MDA are smallest by G35%and greatest by G100%.