七氟醚、异氟醚不同呼气末浓度对熵和脑电双频指数的影响

目的 观察不同呼气末浓度的七氟醚和异氟醚对熵、脑电双频指数(BIS)及血流动力学的影响.方法 40例ASA Ⅰ或Ⅱ级全麻手术患者随机均分为七氟醚组(Ⅰ组)和异氟醚组(Ⅱ组).麻醉诱导用丙泊酚1 mg/kg,1 min后吸入七氟醚或异氟醚;维持反应熵(RE)、状态熵(SE)、BIS45～55,6 min后置入喉罩.调节吸入浓度使两组患者呼气末浓度分别为0.4、0.6、0.8、1.0和1.3MAC时各维持10 min,记录RE、SE、BIS、HR和MAP.结果 两组患者不同呼气末浓度七氟醚和异氟醚RE、SE、BIS随浓度增加而逐渐下降(P<0.05),HR逐渐减慢、MAP逐渐降低(P<0.05).两组间各指标差异均无统计学意义.RE、SE、BIS间直线相关性随呼气末浓度增大相关系数有增加趋势.结论 熵和BIS均能有效监测七氟醚、异氟醚麻醉深度.     

七氟醚和依托咪酯镇静催眠效应的相互作用

目的 评价七氟醚和依托咪酯镇静催眠效应的相互作用.方法 择期全麻手术患者24例,ASA Ⅰ或Ⅱ级,年龄18～59岁,体重指数17～27 kg/m2.试验Ⅰ 12例患者靶控输注依托咪酯,效应室靶浓度依次为0.05、0.1、0.2、0.3、0.4、0.5 μg/ml.效应室浓度依次达到预设浓度2 min时,记录反应熵(RE)、状态熵(SE)和警觉/镇静(OAA/S)评分,然后停止输注依托咪酯.随机分为3组(n=4),A1组、B1组、C1组吸入七氟醚,呼气末浓度分别为0.5%、1%、2%.七氟醚呼气末浓度达预定浓度的95%或以上时,靶控输注依托咪酯,效应室靶浓度依次为0.2、0.3、0.4、0.5 μg/ml.效应室浓度依次达到预设浓度2 min时,记录RE、SE和OAA/S评分.试验Ⅱ 12例患者吸入七氟醚,呼气末浓度依次为0.5%、1%、2%、3%、4%、5%.依次达到预定呼气末浓度时,记录RE、SE和OAA/S评分,然后停止吸人七氟醚,吸氧洗脱七氟醚.随机分为3组(n=4),A2组、B2组、C2组靶控输注依托咪酯,效应室靶浓度分别为0.05、0.1、0.2 μg/ml.效应室浓度达到预设浓度2 min时,吸入七氟醚,呼气末浓度依次为0.5%、1%、2%、3%、4%、5%.依次达到预定呼气末浓度时,记录RE、SE和OAA/S评分.采用反应曲面法评价RE、SE和OAA/S评分,判断七氟醚和依托咪酯镇静催眠效应的相互作用.结果 RE和SE的相互作用指数的拟合值及其95%可信区间分别为0.32(-0.07～0.71)、0.25(-0.12～0.63)(P>0.05).OAA/S评分的相互作用指数的拟合值及其95%可信区间为2.25(0.58～3.93)(P<0.05).结论 以脑电熵指数反映镇静催眠效应时七氟醚和依托咪酯为相加作用;以OAA/S评分反映镇静催眠效应时七氟醚和依托咪酯为协同作用.     

七氟醚与异氟醚苏醒期熵指数和听觉诱发电位指数的相关性

目的观察七氟醚和异氟醚苏醒期熵指数(RE和SE)与听觉诱发电位指数(AAI)的变化和相关性。方法择期行腹腔镜下胆囊或子宫附件切除术患者30例,随机均分为七氟醚组(S组)和异氟醚组(I组),分别持续吸入2%～3%七氟醚和异氟醚维持麻醉。吸入麻醉药停止后,20min内每隔1分钟记录RE、SE与AAI,并分析其相关性。结果苏醒期RE、SE与AAI均呈逐渐上升趋势,Ⅰ组相关系数分别为0.89和0.91(P<0.05);S组相关系数分别为0.93和0.91(P<0.05)。结论熵指数和AAI均能反映七氟醚和异氟醚苏醒期麻醉深度的变化,两者相关性良好。     

七氟醚与丙泊酚对冠心病患者行非心脏手术心肌的影响

目的 比较冠心病患者行非心脏手术时七氟醚与丙泊酚对心肌的影响.方法 40例心功能Ⅰ或Ⅱ级择期行上腹部手术的冠心病患者随机分为丙泊酚组(PR组)与七氟醚组(SE组).PR组丙泊酚靶控输注血药浓度维持在2～3μg/ml,SE组呼气末七氟醚浓度维持在2%～3%,连续监测血流动力学及ECC变化,检测麻醉前与术毕血清白细胞介素-6(IL-6)、肿瘤坏死因子α(TNF-α)、心肌钙蛋白(cTnI)及糖原磷酸化酶BB(GP-BB)浓度.结果 术毕PR组血清IL-6、TNF-α、cTnI及GP-BB浓度明显高于麻醉前及SE组(P＜0.05).结论 冠心病行非心脏手术时七氟醚对心肌的保护效应优于丙泊酚.     

熵指数监测全麻患者镇静水平的准确性

目的 评价反应熵和状态熵监测全麻患者镇静水平的准确性.方法 择期行腹部手术患者20例,ASAⅠ或Ⅱ级,入室后监测反应熵(RE)、状态熵(SE)及脑电双频谱指数(BIS),静脉注射异丙酚、维库溴铵和芬太尼麻醉诱导,气管插管后机械通气,吸入七氟烷、间断静脉注射维库溴铵和芬太尼维持麻醉.分别于入室时、意识消失前10min、意识消失即刻、气管插管时、手术1 h、意识恢复前10 min、意识恢复即刻、拔管后10 min时记录RE、SE和BIS.结果 RE、SE和BIS在意识改变前后差异均有统计学意义(P＜0.05),RE、SE和BIS判断意识消失的临界值分别为76、73和68,灵敏度分别为94%、95%和92%,特异度分别为92%、94%和9l%,临界值判断意识消失的准确度分别为93%、95%、94%;判断意识恢复的临界值分别为82、75和70,灵敏度分别为95%、95%和91%,特异度分别为93%、96%和93%,临界值判断意识恢复的准确度分别为98%、96%和97%.结论 熵指数能够准确地监测全麻患者镇静水平.     

七氟醚浓度和BIS指数的“滞后”效应测量显示肥胖不影响七氟醚作用起效和消除

背景肥胖患者的呼吸以及气体交换的生理改变可能导致麻醉气体作用的起效和消除延迟。本研究评估了肥胖对七氟醚及BIS值之间“滞后”效应的影响。因为呼气末正压（positiveend-expiratorypressure,PEEP）可改善肥胖患者的气体交换,所以我们也同时评估了PEEP对该“滞后”效应的影响。方法前瞻性研究了15例肥胖和15例体重正常的ASAI级和Ⅱ级、20-50岁、择期行全麻下腹腔镜手术的患者。麻醉诱导使用丙泊酚,维持使用七氟醚和芬太尼。手术结束后将BIS值维持稳定在60～65,然后将七氟醚吸入浓度增加至5v01％,持续5分钟或至BIS〈40为止,然后降低吸入浓度。正常体重患者七氟醚浓度变换一次（无PEEP）,肥胖患者浓度变换两次（一次无PEEP,一次PEEP=8cm H2O）。七氟醚浓度变换期间七氟醚呼末浓度和BIS之间的“滞后”效应通过抑制性Emax模型建模,使用的是NONEMN（非线性混合效应模型）第VI版的群体药代动力学／药效动力学（pharmacokinetic／pharmacodynamic．PK／PD）方法。对七氟醚吸入和呼出浓度、BIS值和达不同BIS终点的时间等指标的描述性分析也被用于比较PK和PD特征。结果所有患者均完成研究。数据完全符合PK／PD模型。体重指数或PEEP对“滞后”效应无影响（P〉0．05）,“滞后”效应使用效应室消除率常数表示。肥胖和PEEP均未显示对PK／PD的相关指标有影响。结论结果未显示七氟醚（低血溶解度麻醉药）吸入麻醉90～120分钟后肥胖患者的诱导或恢复时间将延长。     

脑电双频谱指数和脑电熵指数监测全麻患者镇痛水平的评价

目的 评价脑电双频谱指数(BIS)和脑电熵指数监测全麻患者镇痛水平的可行性.方法 择期全麻腹部手术患者26例,随机分为2组(n=13):试验组和对照组.常规监测行硬膜外置管后,试验组硬膜外注入1%利多卡因5 ml,对照组注入等量生理盐水,8 min后测定阻滞平面,根据结果试验组硬膜外追加1%利多卡因和0.5%罗哌卡因的混合制剂5～10 ml,对照组硬膜外追加生理盐水8 ml.麻醉诱导前确保试验组的感觉阻滞节段超过手术切口范围.连接BIS监测仪和脑电熵指数监测仪监测BIS、状态熵(SE)和反应熵(RE).靶控输注异丙酚(初始血浆靶浓度4 μg/ml)和瑞芬太尼(效应室靶浓度2 ng/ml)进行全麻诱导,调整异丙酚靶浓度,维持BIS 40～50.静脉注射罗库溴铵0.9 mg/kg,气管插管,机械通气,试验组停止输注瑞芬太尼,对照组继续输注瑞芬太尼,效应室靶浓度为2 ng/ml.切皮前3 min每分钟记录BIS、RE、SE、HR、SP、DP、MAP,取其平均值作为基础值,切皮后2 min内要求外科医师停止包括使用电刀在内的手术操作,每分钟记录上述指标.2 min后开始使用电刀,进行正常手术操作,并继续每分钟记录上述指标直到切皮后6 min,取其平均值.结果 与基础值比较,切皮后1 min时对照组BIS、RE-SE、SP、DP和MAP均升高(P＜0.05),试验组各指标差异无统计学意义(P＞0.05),切皮后3～6 min内2组BIS、RE和RE-SE均升高,对照组BP升高(P＜0.05).切皮后1min.对于判断镇痛是否足够的准确性,△SP＞△RE-SE＞△MAP＞△BIS,判断准确性均中等.而在电刀干扰时,只有BP的变化可以作为判断指标区分不同的分组,△SP＞△MAP.结论 BIS、熵指数和BP并不能反映镇痛水平,但BIS、RE-SE和BP都能够在镇痛不足的情况下对伤害性刺激表现出明显升高.对于镇痛不足的判断准确性,△SP＞△RE-SE＞△BIS,准确性均中等.     

频谱熵和双频指数用于测定依托咪酯血浆效应室平衡速率常数的比较

目的 比较用熵指数和脑电双频指数(BIS)测定依托咪酯单次注射后的最大效应时间(TpEAK),并藉以估计依托咪酯的血浆-效应室平衡速率常数(Ke0).方法 22例患者静脉注射最大效应负荷剂量依托咪酯后,用熵指数模块和听觉诱发电化监测仪测定从注射开始至反应熵(RE)、状态熵(SE)、BIS最低的时间(TPEAK),用TpEAx和Arden等报道的依托咪酯药代学模型,按照Minto等提出的方法计算KeO.结果 RE、SE、BIS的TpEAx中位数分别为70、70和80 s,Ke0中位数分别是1.10/min、1.10/min和1.02/min.结论 单次注射依托咪酯后,熵指数和BIS监测的TpESK和计算的Ke0相同,且有别于国外研究报道的结果.     

小剂量氯胺酮对脑电熵指数和脑电双频指数的影响

目的比较小剂量氯胺酮对脑电熵指数(RE、SE)和脑电双频指数(BIS)的影响。方法22例ASAⅠ或Ⅱ级择期行腹腔镜子宫切除术及卵巢囊肿切除术患者,随机均分为氯胺酮组(K组)和生理盐水组(S组)。麻醉诱导:丙泊酚1～2mg/kg、雷米芬太尼1～1.5μg/kg和维库溴铵0.1～0.15mg/kg,气管插管。麻醉维持:丙泊酚6～8mg.kg-1.h-1、维库溴铵0.1mg.kg-1.h-1和雷米芬太尼7～10μg.kg-1.h-1。在稳定的麻醉和手术状况下,分别单次给予患者氯胺酮0.5mg/kg(K组)或等量的生理盐水(S组),记录给药前(基础值)、给药后5、10、15、20、25和30min七个时点MAP、HR、RE、SE和BIS的数值。结果K组和S组MAP、HR、RE、SE和BIS的基础值差异均无统计学意义。K组RE、SE和BIS在给药后迅速升高,然后逐渐下降,在给药后10min达到峰值,分别比基础值升高了43.8%(P<0.01)、43.2%(P<0.01)和28.8%(P<0.01)。RE和SE增加的幅度显著高于BIS,熵指数和BIS增加持续的时间分别为25min和20min。S组在给药后RE、SE和BIS值与基础值相比差异均无统计学意义。K组和S组在给药前后MAP和HR变化差异无统计学意义。结论在丙泊酚-雷米芬太尼麻醉期间,单次加入小剂量的氯胺酮,熵指数和BIS均不能准确反映其真正的麻醉深度。     

七氟醚、异氟醚和地氟醚对神经外科手术患者经颅电刺激运动诱发电位的影响

目的 比较七氟醚、异氟醚和地氟醚对神经外科手术患者经颅电刺激运动诱发电位(MEPs)的影响.方法 择期行神经外科手术患者60例,年龄18～64岁,ASA分级Ⅰ或Ⅱ级.随机分为3组(n=20):七氟醚组、异氟醚组和地氟醚组.监测BIS值和经颅电刺激MEPs.调节七氟醚、异氟醚和地氟醚吸入浓度,使其呼气末浓度分别达到0.50、0.75、1.00和1.30 MAC,每一浓度均维持15 min,视为稳态呼气末浓度.于给予吸入麻醉药前(基础状态)和达到各稳态呼气末浓度(T1-4)时,记录MEPs的波幅和潜伏期以及BIS值.记录MEPs波形记录失败情况.结果 与七氟醚组和异氟醚组比较,地氟醚组T1.2时波幅和BIS值降低,T1-4时潜伏期延长(P＜0.05);七氟醚组和异氟醚组各指标比较差异无统计学意义(P＞0.05).七氟醚组、异氟醚和地氟醚组基础状态、T1、T2时的记录失败率均为0;T3时记录失败率分别为0、5%和20%,三组比较差异无统计学意义(P＞0.05);T4时记录失败率分别为5%、20%和45%,与七氟醚组和异氟醚组比较,地氟醚组记录失败率升高(P＜0.05);七氟醚组和异氟醚组比较差异无统计学意义(P＞0.05).结论 地氟醚对神经外科手术患者经颅电刺激MEPs的抑制作用强于七氟醚和异氟醚.术中行MEPs监测时,七氟醚和异氟醚适宜的呼气末浓度为1.00 MAC,地氟醚为0.75～1.00 MAC.     

Pharmacokinetic-pharmacodynamic modeling the hypnotic effect of sevoflurane using the spectral entropy of the electroencephalogram

Spectral entropy is a new electroencephalogram (EEG)-derived parameter that may be used to model the pharmacokinetic-pharmacodynamic (PKPD) effects of general anesthetics. In the present study we sought to derive a PKPD model of the relationship between sevoflurane concentration and spectral entropy of the EEG. We collected spectral entropy data during increasing and decreasing sevoflurane anesthesia from 20 patients. The first cycle consisted of induction and lightening phases with no supplemental medications. An effect-site compartment and inhibitory E(max) model described the relation between sevoflurane concentration and spectral entropy. PKPD parameters were derived from the full cycle and separately from the increasing and decreasing stages. The second anesthetic cycle consisted of a redeepening phase only and included airway manipulation and routinely administered adjunctives. PKPD data obtained from the first cycle were used to predict second cycle entropy changes. There was a consistent relationship between effect-site sevoflurane concentration and spectral entropy (median absolute weighted residual = 11.6%). For complete first-cycle response entropy (mean +/- sd): T1/2 K(eo) = 2.4 +/- 1.5 min, gamma = 5.9 +/- 2.3, EC50 = 1.7 +/- 0.3. We found significant differences between gamma values when the sevoflurane concentration was increasing (61.1 +/- 55.2) compared with the decreasing part of the cycle (5.7 +/- 2.8). Above an effect-site concentration of 3%, spectral entropy of the EEG is unresponsive to further increases in sevoflurane concentration. The effect-compartment inhibitory E(max) model accurately describes the relation between sevoflurane concentration and spectral entropy of the EEG. Spectral entropy decreases with increasing sevoflurane concentrations up to 3%. The steepness of the dose-response curve varies between phases of increasing and decreasing anesthetic concentrations.     

Spectral entropy monitoring allowed lower sevoflurane concentration and faster recovery in children

Background: Anesthetic titration using spectral entropy monitoring reduces anesthetic requirements and shortens recovery in adult surgical patients. This study was performed to evaluate the effect of entropy monitoring on end‐tidal sevoflurane concentration and recovery characteristics in pediatric patients undergoing sevoflurane anesthesia. Methods: Seventy‐eight children (aged 3–12 years) scheduled for a tonsillectomy and/or an adenoidectomy were randomly divided into one of two groups: standard practice (Standard) or entropy‐guided (Entropy). In the Standard group, sevoflurane was adjusted to maintain the heart rate and systolic blood pressure (BP) within 20% of the baseline values. In the Entropy group, sevoflurane was adjusted to achieve a state entropy of 40–50. We compared the entropy values, end‐tidal sevoflurane concentration and recovery times between groups. Results: During maintenance of anesthesia, the entropy and BP values were higher in the Entropy group (P<0.05). The end‐tidal sevoflurane concentration during maintenance was lower in the Entropy group (2.2 (0.3) vol%) compared with the Standard group (2.6 (0.4) vol%) (P<0.05). Recovery times were faster in the Entropy group (P<0.05). Conclusions: Compared with standard practice, we found that entropy‐guided anesthetic administration was associated with a reduced sevoflurane concentration and a slightly faster emergence and recovery in 3–12‐year‐old children.     

Does monitoring bispectral index or spectral entropy reduce sevoflurane use?

A decrease in volatile anesthetic consumption has been demonstrated using bispectral index (BIS), whereas data concerning spectral entropy are lacking. One hundred and forty adult patients scheduled for surgical procedures lasting more than 1 h were prospectively randomized to receive an anesthetic controlled either by BIS or by spectral entropy or solely by clinical variables. Anesthesia was induced with propofol and sufentanil. Sufentanil was infused continuously thereafter. Sevoflurane was administered in 1 L/min O2/N2O. The sevoflurane concentration was adjusted according to conventional clinical variables in the standard practice group, whereas the 40-60 interval was applied for the BIS and spectral entropy-guided groups. The sevoflurane vaporizer was weighed before and after anesthesia, and consumption was calculated. Groups were comparable for demographic data except for weight (heavier in the spectral entropy-guided group, P < 0.05). Compared with standard practice, patients with BIS or spectral entropy monitoring required 29% less sevoflurane (normalized sevoflurane consumption to the weights of the patients and to the durations of anesthesia; both P < 0.03) and a similar sufentanil dose. An unintended improvement in the standard practice group (positive bias) was observed. In conclusion, BIS and spectral entropy monitoring have the same sparing effect of sevoflurane.     

Using Permutation Entropy to Measure the Electroencephalographic Effects of Sevoflurane

Background: Approximate entropy (AE) has been proposed as a measure of anesthetic drug effect in electroencephalographic data. Recently, a new method called permutation entropy (PE) based on symbolic dynamics was also proposed to measure the complexity in an electroencephalographic series. In this study, the AE and PE were applied to electroencephalographic recordings for revealing the effect of sevoflurane on brain activity. The dose-response relation of PE during sevoflurane anesthesia was compared with that of AE.

Methods: Nineteen patients' electroencephalographic data were collected during the induction of general anesthesia with sevoflurane. PE and AE were applied to the electroencephalographic recordings, and the performance of both measures was assessed by pharmacokinetic-pharmacodynamic modeling and prediction probability. To ensure an accurate complexity measure of electroencephalographic recordings, a wavelet-based preprocessor was built in advance.

Results: Both PE and AE could distinguish between the awake and anesthetized states and were highly correlated to each other (r = 0.8, P = 0.004). The pharmacokinetic-pharmacodynamic model adequately described the dose-response relation between PE and AE and sevoflurane effect site concentration. The coefficient R2 between PE and effect site concentration was 0.89 +/- 0.07 for all patients, compared with 0.60 +/- 0.14 for AE. Prediction probabilities of 0.86 +/- 0.04 and 0.79 +/- 0.09 for PE and AE showed that PE has a stronger ability to differentiate between the awake and anesthetic states.     

Concentration-Effect Relations, Prediction Probabilities (Pk), and Signal-to-noise Ratios of Different Electroencephalographic Parameters during Administration of Desflurane, Isoflurane, and Sevoflurane in Rats

Background: The authors investigated the suitability of different electroencephalographic parameters to quantify the anesthetic effect of desflurane, isoflurane, and sevoflurane in rats.

Methods: Ten male Sprague-Dawley rats were anesthetized in a randomized crossover design with maximum values of 11% desflurane, 2.1% isoflurane, and 3.5% sevoflurane. The electroencephalogram was recorded with implanted electrodes and a wireless telemetry system. Concentration-effect relations and signal-to-noise ratios were determined for the approximate entropy and for the median frequency and the spectral edge frequency, which were modified to account for spikes and burst suppression. The prediction probability Pk with respect to the response to a painful stimulus was determined.

Results: All drugs produced deep anesthesia with burst suppression and no response at the highest concentrations. The occurrence of spikes and burst suppression made a modification of median frequency and spectral edge frequency necessary to obtain Pk values greater than 0.5 and monotonic sigmoid concentration-effect relations. The Pk values were between 0.89 and 0.98, with significantly higher values for modified median frequency and spectral edge frequency during desflurane and sevoflurane. The signal-to-noise ratios were between 3.0 and 6.4 dB, with significantly better values for modified spectral edge frequency and approximate entropy during sevoflurane.     

Spectral entropy and bispectral index as measures of the electroencephalographic effects of sevoflurane

BACKGROUND: Recently, entropy algorithms have been proposed as electroencephalographic measures of anesthetic drug effects. Datex-Ohmeda (Helsinki, Finland) introduced the Entropy Module, a new electroencephalographic monitor designed for measuring depth of anesthesia. The monitor calculates a state entropy (SE) computed over the frequency range of 0.8-32 Hz and a response entropy (RE) computed over the frequency range of 0.8-47 Hz. The authors investigated the dose-response relation of SE and RE during sevoflurane anesthesia in comparison with the Bispectral Index (BIS). METHODS: Sixteen patients were studied without surgical stimulus. Anesthesia was induced by sevoflurane inhalation with a tight-fitting facemask. Sevoflurane concentrations were increased and subsequently decreased and increased two to four times until the measurement was stopped and patients were intubated for surgery. The performances of SE, RE, and BIS to predict the estimated sevoflurane effect site concentration, obtained by simultaneous pharmacokinetic and pharmacodynamic modeling, were compared by calculating the correlation coefficients and the prediction probability. RESULTS: State entropy, RE, and BIS values decreased continuously over the observed concentration range of sevoflurane. Correlation coefficients were slightly but not significantly better for entropy parameters (0.87 +/- 0.09 and 0.86 +/- 0.10 for SE and RE, respectively) than for BIS (0.85 +/- 0.12). Calculating the prediction probability confirmed these results with a prediction probability of 0.84 +/- 0.05 and 0.82 +/- 0.06 for SE and RE, respectively, and 0.80 +/- 0.06 for BIS. CONCLUSION: State entropy and RE seem to be useful electroencephalographic measures of sevoflurane drug effect.     

Influence of age on hypnotic requirement, bispectral index, and 95% spectral edge frequency associated with sedation induced by sevoflurane

BACKGROUND: Aging is associated with a reduction in anesthetic requirements. The effects of age on the electroencephalographic response to inhalational anesthesia have not been well documented. The objective of the present study was to determine the influence of age on hypnotic requirement and electroencephalographic derivatives such as bispectral index and 95% spectral edge frequency associated with sedation induced by sevoflurane. METHODS: Ninety-six patients were randomly allocated into one of three age groups A, B, and C, ranging in age from 18-39 yr, 40-64 yr, and 65-85 yr, respectively. Patients in each group were sedated with sevoflurane at two predetermined concentrations ranging between 0.45% and 0.85%. The relationship between sevoflurane concentration and response to a verbal command, as well as the relationships between response and bispectral index and 95% spectral edge frequency, was determined. RESULTS: Multiple regression analysis showed that end-tidal sevoflurane concentration and age significantly affected both bispectral index and 95% spectral edge frequency. ED50 values of sevoflurane concentration for loss of consciousness, defined as no response to verbal command, were different between groups A and C: 0.72 (95% confidence interval: 0.68-0.75) versus 0.59 (95% confidence interval: 0.56-0.62). However, the same effective values of bispectral index and 95% spectral edge frequency at this same clinical end point did not differ. CONCLUSIONS: Increasing age reduced sevoflurane requirements to suppress responses to a verbal command but did not change bispectral index and 95% spectral edge frequency associated with this end point, and in a population with a wide age range, bispectral index would predict depth of sedation better than end-tidal sevoflurane concentration.     

Effects of sevoflurane on mid-latency auditory evoked potentials and the 95% spectral frequency limit

OBJECTIVES: To investigate the effects of sevoflurane on mid-latency auditory evoked potentials (MLAEP) and compare them to changes in the encephalographic 95% spectral edge frequency (SEF95). PATIENTS AND METHODS: The effect of sevoflurane on MLAEP and SEF95 was studied in 15 patients. Anesthetic induction was carried out with propofol, remifentanil, and cisatracurium. After anesthetic induction, the patients were ventilated to achieve different expired concentrations of sevoflurane (1%, 1.5%, and 2%) during 3 consecutive 10-minute periods before the start of surgery. SEF95 and the amplitude and latency of the Na, Pa and Nb MLAEP waves were recorded. All the parameters were measured at baseline and during the different expired fractions of sevoflurane. RESULTS: The increase in sevoflurane concentration was accompanied by a significant decrease in amplitude and a statistically significant increase in latency of the Na, Pa and Nb waves. Likewise, SEF95 decreased significantly. A linear relation was demonstrated between sevoflurane concentration and the variables Na, Pa, Nb and SEF95. CONCLUSIONS: Our results indicate that the effect of sevoflurane on the MLEAP of Na, Pa and Nb is similar to that of other anesthetic gases. Even though the amplitude of the Na, Pa and Nb waves decreased in a dose-dependent way, SEF95 correlated more strongly with sevoflurane concentration.     

Correlation of EEG spectral entropy with regional cerebral blood flow during sevoflurane and propofol anaesthesia

ENTROPY index monitoring, based on spectral entropy of the electroencephalogram, is a promising new method to measure the depth of anaesthesia. We examined the association between spectral entropy and regional cerebral blood flow in healthy subjects anaesthetised with 2%, 3% and 4% end-expiratory concentrations of sevoflurane and 7.6, 12.5 and 19.0 microg.ml(-1) plasma drug concentrations of propofol. Spectral entropy from the frequency band 0.8-32 Hz was calculated and cerebral blood flow assessed using positron emission tomography and [(15)O]-labelled water at baseline and at each anaesthesia level. Both drugs induced significant reductions in spectral entropy and cortical and global cerebral blood flow. Midfrontal-central spectral entropy was associated with individual frontal and whole brain blood flow values across all conditions, suggesting that this novel measure of anaesthetic depth can depict global changes in neuronal activity induced by the drugs. The cortical areas of the most significant associations were remarkably similar for both drugs.