The Effect Of Lipid Emulsion On Central Nervous System Toxicity Of Bupivacaine And The Mechanism Study In Rats

The animal experiments show that lipid emulsion infusion can lessen and reverse heart toxicity of local anesthetic, which is also demonstrated by clinical studies. In the early stage, lipid emulsion therapy not only can prevent cardiovascular toxicity but also relieve nervous system toxicity. However, the mechanism that lipid emulsion remedies general toxicity of local anesthetic is still unclear now. There are a few possible mechanisms:“fat pool mechanism”、“metabolic mechanism”、accelerated metabolism、 diffusion and direct positive myodynamia on cardiac muscle of local anesthetic and so on. This study aims to explore the main mechanism by conducting prospective animal experiments and observing the effect of lipid emulsion on LAST central nervous system toxicity induced by bupivacaine.Section one The effect of lipid emulsion pretreatment on central nervous toxicity by bupivacaine intoxication and the main mechanism in ratsObjectiveTo investigate the effect of lipid emulsion pretreatment on central nervous toxicity of bupivacaine and the main mechanism in SD rats. Methods1.12health SD rats were randomly separated into two groups including sodium chloride pretreatment group (group A) and lipid emulsion pretreatment group (group B).2. Incision of trachea, tracheal intubation, mechanical ventilation, carotid arteriopuncture and femoral venepuncture were conducted after inhalation anesthesia with sevoflurane. ECG, BP, MAP, EEG and HR were recorded during this course.3. After anesthesia for15min, the rats received sodium chloride pretreatment in group A; in group B, the rats received20%lipid emulsion pretreatment. All rats were performed infusion through left femoral vein by micro pump at the speed of3ml/kg/min for5min.4. After that,0.5%bupivacaine was infused through right femoral vein by micro pump at the speed of2mg/kg/min until the first cerebral spasm wave (SZ) presented in electroencephalogram. Then, brain was obtained by instant decapitation. The usage amount of bupivacaine and the time when cerebral spasm wave (SZ) occurred were recorded.5. High performance liquid chromatography was used to detect bupivacaine concentration in brain tissues by liquid-liquid extraction.Results1. There was no statistical difference for basic hemodynamics between these two groups. MAP and HR were104.8±6.8mmHg and296.5±8.2times/min in sodium chloride pretreatment group and104.5±7.7mmHg (P=0.939) and297±8.0times/min (P=0.917) in lipid emulsion pretreatment group respectively.2. The time when cerebral spasm wave (SZ) occurred was evidently longer in lipid emulsion pretreatment group (311.8±30.3s) than that in sodium chloride pretreatment group (158.2±7.9s)(P<0.05). The total usage amount of bupivacaine was also significantly more in lipid emulsion pretreatment group (10.4±1.0mg/kg) than that in sodium chloride pretreatment group (5.3±0.3mg/kg)(P<0.05).3. There was no statistical significance for bupivacaine concentration in brain tissues between these two groups (groupA:6.1±1.4mg/kg,groupB:6.6±0.3mg/kg) (P=0.427).ConclusionLipid emulsion pretreatment can reduce rat’s central nervous toxicity of bupivacaine revealing that "fat pool mechanism" may be the main mechanism.Section two The effect of lipid emulsion post-treatment on partial pharmacokinetics of bupivacaine and the main mechanism in ratsObjectiveTo observe the effect of lipid emulsion post-treatment on bupivacaine concentration in blood plasma and cardiac tissues of SD rats and explore the main mechanism that lipid emulsion pretreatment affects central nervous toxicity of bupivacaine.Methods1.24SD rats were randomly separated into four groups including sodium chloride post-treatment material group (group Cl), sodium chloride post-treatment observation group (group C2), lipid emulsion post-treatment material group (group Dl) and lipid emulsion post-treatment observation group (group D2).2. Incision of trachea, tracheal intubation, mechanical ventilation, carotid arteriopuncture and femoral venepuncture were conducted after inhalation anesthesia with sevoflurane. ECG, BP, EEG and HR were recorded during this course.3. After anesthesia for15min,0.1%bupivacaine was infused through femoral vein by micro pump at the speed of2mg/kg/min for3min in four groups. Then, it needed to draw blood from vein instantly and the rats received post-processing drugs respectively in each group.4. The rats received sodium chloride pretreatment by micro pump in group C1and C2; in group D1and D2, the rats received20%lipid emulsion infusion by micro pump. All infusion was performed at the speed of3ml/kg/min for5min.5.1.5ml arterial blood was gained and reserved in heparinized anticoagulation tubes by drawing arterial blood from carotid artery after infusion instantly and for8min in group Cl and group D1and brain was obtained by instant decapitation.6.1.5ml arterial blood was gained and reserved in heparinized anticoagulation tubes by drawing arterial blood from carotid artery after infusion for Omin、8min、25min、50min and75min in group C2and group D2and brain was obtained by instant decapitation.7. The way to draw standard curve was that lml pooled serum of animal subjects was added into a series of standard liquid of bupivacaine respectively to prepare0.0625mg/L、0.125mg/L、0.25mg/L、0.5mg/L、1.0mg/Land4mg/Lof serum sample and high performance liquid chromatography was used to detect peak area of bupivacaine with linear regression as peak area to added concentration.Results1. Linear relation was preferable when peak area and plasma concentration of bupivacaine were0.0625mg/L-4mg/L. Y=0.0000359X+0.00938(r=0.999, n=5).2. The plasma concentration of bupivacaine was higher in lipid emulsion post-treatment group (D1)15.09±0.45mg/L than that in sodium chloride post-treatment group (C1)5.19±0.41mg/L at the time point8min. There was statistical significance for bupivacaine concentration in plasma between Cl and D1(P<0.05). The plasma concentration of bupivacaine were higher in lipid emulsion post-treatment group (D2)(0min6.93±0.55mg/L、8min15.18±0.38mg/L、25min7.41±0.41mg/L、50min4.32±0.28mg/L、75min2.13±0.13mg/L) than that in sodium chloride post-treatment group (C2)(0min6.95±0.53mg/L、8min5.2±0.45mg/L、25min2.57±0.09mg/L、50min1.50±0.09mg/L、75min1.04±0.17mg/L) at the same time point except Omin. There were statistical significance for bupivacaine concentration in plasma between C2and D2except Omin (P<0.05).3. There was statistical significance for bupivacaine concentration in brain tissues between group C1and group D1and it was higher in sodium chloride post-treatment group (C1:2.37±0.052μ g/g) than that in lipid emulsion post-treatment group (D1:1.39±0.499μ g/g)(P<0.05). There was statistical significance for bupivacaine concentration in brain tissues between group C2and group D2and it was higher in sodium chloride post-treatment group (C2:0.320±0.035μ g/g) than that in lipid emulsion post-treatment group (D2:0.157±0.027μ g/g)(P<0.05)ConclusionsLipid emulsion post-treatment can increase rat’s plasma (whole blood) bupivacaine concentration and reduce its concentration in brain tissues instantly, suggesting that it has great effect on bupivacaine pharmacokinetics "fat pool effect". Fat pool mechanism has potential to be the main mechanism that lipid emulsion remedies rat’s central nervous toxicity by bupivacaine intoxication.