EEG Nonlinear Indexes Monitoring Perioperative Cerebral Function

Part One:Comparison of the prediction probability of loss of consciousness of the EEG nonlinear indexes and the bispectral index during the sedation by the target -controlled infusion of propofolObjective To study the changes of electroencephalogram(EEG) nonlinear indexes (include Correlation dimension ,D₂;Approximate entropy ,ApEn;Complexity,Cx. ) and the bispectral index(BIS) during the sedation produced by target-controlled infusions(TCI) of propofol. To compare the prediction probability (Pk ) of loss of consciousness (LOC) among the four EEG indexes and their relative accuracy. Methods Twenty patients(ASA I — II grades) aged 22-71 undergoing the elective operations on lower limber under epidural anesthesia. All patients were unpremedicated . Noninvasive blood pressure(NIBP),pulse oxygen saturation (SpO₂),heart rate(HR) and electrocardiogram(ECG) were monitored as regular. The upper limber venous was cannulated for fluid replacement.Epidural cather was placed at L_2,3 or L_3,4 interspace.The block height was 6.Oxygen was given during anesthesia via nasal tube or mask. SpO₂ was maintained >95%.The target plasma concentration of propofol(Cp) was initially set at 0.5ug.ml^-1.Cp was gradu-ally increased in increment of 0. 3 0.5μg.mr^-1 until LOC.Depath of sedationwas assessed by Observe Alert Assessment/Sedation(OAA/S) scale(5=alert,1=LOC).Cp was equal to the effect-site concentration of propofol(Ce) when the patients LOC immediately.LOC was maintained for 12 min.Cp was then gradually deer-eased in decrement of 0. 3 0.5ug?mr' untill the patients regained consciousness.Cp was equal to Ce when the patients was consciousness immediately. Conscious -ness was also maintained 12 min.The same procedure was repeated four times. BIS ,D2,ApEn and Cx were recorded simultaneously in the stages of conscious -ness and LOC every 3 minutes. The prediction probability of LOC for D2, ApEn, Cx and BIS was calculated and compared.Result Before TCI ,the BIS value was 97±1.34;D2 was 3.93±0.08;ApEn was 1.01±0.05;Cx was 0.65±0.03.The BIS value was $0.2±6.2 when the patient regained consciousness(Ti) and 67.3±7.9 at LOC(T2);D2 was 3.45±0.18 (T,)and 3.01±0.16XT2);ApEn was 0.84±0.05 (T,) and 0.71±0.06(T2);Cx was 0.55±0.05(T,) and 0.44±0.05(T2).Four EEG indexes value was higher before TCI sedation than in Tland T2 stages. Four EEG indexes value was higher in Ti stages than in T2 stages(P<0.05),but the value scope was overlaping.The prediction probability of D2, ApEn,Cx and BIS were 0.96,0.97,0.94 and 0.91 respectively at LOC.There was no different in Pk of LOC among the four indexes (P>0.05). Conclusion BIS,D2>ApEn and Cx can all distinguish the change between consciousness and LOC produced by TCI of propofol.Our findings suggest that the four EEG index can monitor the central sedation effect of propofol.Part Two: Compare the EEG nonlinear index between the patients of cerebral infarction and the healthy control subjiectsObject To compare EEG nonlinear indexes( Correlation dimension , D2;Approximate entropy, ApEn;Complexity,Cx.) between the patients of cerebral infarction and the healthy control subjects.To identify whether the cerebral infarction can be monitored by the EEG nonlinear indexes. Method Thirty patients of cerebral infarction, which had been verified by brain magnetic resonance imaging(MRI),aged 5 5± 14, were selected.Twenty-two patients are male.Eight patients are female.The measurement of brain MRI and EEG nonlinear indexes had been done simulataneously in a week since cerebral infarction was onset.Thirty healthy subjects,whose gender and age was same as the patients of cerebral infarction,were selected.There was no disease of nervous system and mental discord in healthy subjects.Any agents to influence EEG had been excluded.The subjects in two groups sitted in quiet room.After they closed eyes and had a rest with normal respiratory rhythm for ten minutes,EEG nonlinear indexes(D2,ApEn,Cx) in forehead (Fpl,Fp2) were measured.EEG nonlinear indexes between two groups was compared by paired-t test. Result In the patients of cerebral infarction group,the D2 value was 3.09 ± 0.41 (Fpl) and 3.03±0.40(Fp2),the ApEn value was 0.81 ±0.14(Fpl) and 0.78±0.12 (Fp2),the Cx value was 0.43±0.09(Fpl) and 0.43±0.07(Fp2).In the healthy subjects control group, the D2 value was 4.06±0.30(Fpl) and 4.13 ±0.4l(Fp2), the ApEn value was 1.09±0.12(Fpl) and 1.09±0.12(Fp2),the Cx value was 0.67±0.06JFpl) and 0.68 ± 0.07(Fp2).The value of D2,ApEn,Cx was all lower in the patients of cerebral infarction than the healthy subjects.There was significant difference in EEG nonlinear indexes between two groups(P<0.05).In the patients of cerebral infarction group,there was significant difference in the value of D2and ApEn between Fpl and Fp2 (P<0.05),but there was no significant difference inthe Cx value. In the healthy subjects control group,there was no significant difference in the EEG nonlinear indexes value between Fpl and Fp2 . Conclusion The EEG nonlinear indexes can used to monitor the cerebral infarction. There may be some correlation between the extent of cerebral infarction and the value of D2 and ApEn.Part three:Changes of EEG nonlinear indexes in rat of focal cerebral infarctionObjective To investigate the changes of EEG nonlinear indexes( Correlation dimension , D2;Approximate entropy, ApEn;Complexity,Cx.) in rats of focal cerebral infarction. To identify whether the emergence of cerebral infarction can be monitored by the EEG nonlinear indexes.Methods Twenty-four Sparague-Dawley(SD) rats of either sex, weighted 250-300 gram, were selected.They were randomly divided into two groups:rats of focal cerebral infarction group in which middle cerebral artery of rats were occluded(Group I , n=12), control group in which sham operation was done(GroupII ,n=12). Cranium of rats was perforted in parietal area(C3,C4).The electrodes were planted to the dura mater of rats.D2. ApEn and Cx were recorded in parietal area(C3,C4) of rats of focal cerebral infarction before infarction,and infarction immediately ,and S,15,30,60min after infarction simultaneously.The same measure was done in control group at the same time. Results Group I : EEG nonlinear indexes between C3 and C4 were not different before infarction and rised after infarction. EEG nonlinear indexes in ischemia area(C4) were all lower than in non-ischemia area(C3)(P<0.05). EEG nonlinear indexes in both sides were all decreasing with time elapsing. D2, ApEn and Cx in ischemia area(C4) were lower at 30min after infarction than pre-infarction(P<0.05).Group II: D2, ApEn and Cx were not different significantly at all moment.There was also no difference between C3 and C4. D2, ApEn and Cx were not different significantly between Group I (pre-infarction)and Group II (sham operation).Concultion EEG nonlinear indexes( D2,ApEn and Cx) can monitor the emergence of focal cerebral infarction of rats.They may be assess the extent of cerebral ischemia after infarction.