Comparative evaluation of the Datex-Ohmeda S/5 Entropy Module and the Bispectral Index monitor during propofol-remifentanil anesthesia

BACKGROUND: Different analytical concepts were introduced to quantify the changes of the electroencephalogram. The Datex-Ohmeda S/5 Entropy Module (Datex-Ohmeda Division, Instrumentarium Corp., Helsinki, Finland) was the first commercial monitor based on the entropy generating two indices, the state entropy (SE) and the response entropy (RE). The aim of the current study was to compare the accuracy of SE and RE with the Bispectral Index(R) monitor (BIS(R); Aspect Medical Systems, Newton, MA) during propofol-remifentanil anesthesia. METHODS: The authors investigated 20 female patients during minor gynecologic surgery. SE, RE, BIS, mean arterial blood pressure, heart rate, and sedation level were recorded every 20 s during stepwise increase (target-controlled infusion, 0.5 microg/ml) of propofol until the patients lost response. Five minutes after loss of response, remifentanil infusion (0.4 microg . kg(-1) . min(-1)) was started. Spearman correlation coefficient and prediction probability were calculated for sedation levels with SE, RE, BIS, mean arterial blood pressure, and heart rate. The ability of the investigated parameters to distinguish between the anesthesia steps awake versus loss of response, awake versus anesthesia, anesthesia versus first reaction, and anesthesia versus extubation was analyzed with the prediction probability. RESULTS: SE correlates best with sedation levels, but no significant differences of the prediction probability values among SE, RE, and BIS were found. The prediction probability for all investigated steps of anesthesia did not show significant differences among SE, RE, and BIS. SE, RE, and BIS were superior to mean arterial blood pressure and heart rate. CONCLUSION: SE, RE, and BIS revealed similar information about the level of sedation and allowed the authors to distinguish between different steps of anesthesia. Both monitors provided useful additional information for the anesthesiologist.     

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.     

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.     

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

Recently, Datex-Ohmeda introduced the Entropy Moduletrade mark for measuring depth of anesthesia. Based on the Shannon entropy of the electroencephalogram, state entropy (SE) and response entropy (RE) are computed. We investigated the dose-response relationship of SE and RE during propofol anesthesia in comparison with the Bispectral Indextrade mark (BIS). Twenty patients were studied without surgical stimulus. Anesthesia was induced by a constant propofol infusion of 2000 mg/h (451 +/- 77 microg x min(-1) x kg(-1)) via a large forearm vein. Propofol was infused until substantial burst suppression occurred (more than 50%) or mean arterial blood pressure decreased to <60 mm Hg. Hereafter, infusions were stopped until recovery of BIS values up to 60 was reached. Subsequently, the constant propofol infusion of 2000 mg/h was restarted to increase depth of anesthesia and again decreased (infusion was stopped) within the BIS value range of 40-60. The coefficient of determination (R2) and the prediction probability (P(K)) were calculated to evaluate the performance of SE, RE, and BIS to predict changing propofol effect-site concentrations. R2 values for SE, RE, and BIS of 0.88 +/- 0.08, 0.89 +/- 0.07, and 0.92 +/- 0.06, respectively, were similar. The calculated P(K) values, however, revealed a significant difference between SE and RE compared with BIS, with P(K) = 0.77 +/- 0.09, 0.76 +/- 0.10, and 0.84 +/- 0.06, respectively. BIS seems to show slight advantages in predicting propofol effect-site concentrations compared with SE and RE, as measured by P(K) but not as measured by R2.     

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.     

听觉诱发相关电位，脑电双频指数和熵用于判断重症监护病房患者的不同镇静状态

背景包括镇静评分和常规镇静暂停在内的镇静方案,有助干减少机械通气时间和重症监护病房（ICU）入住时间。因临床上对于镇静深度的评估工作量大、仅能间断进行且干扰镇静和睡眠,所以通过脑电生理信号评估镇静深度的替代方法已经开始倍受青睐：我们想明确听觉诱发相关电位（ERPs）、脑电双频指数（BIS）和墒（Entropy）是否也能够评估临床镇静深度。方法选择10例择期全麻下行胸部或腹部手术的患者。手术后进入ICU,逐渐减少丙泊酚和瑞芬太尼靶控镇静程度[采用Rickmond Agitation镇静评分（RASS）,-5分极深镇静,-4分深度镇静,-3～-1分中度镇静,0分清醒]期间,记录脑电图、BIS、状态熵（SE）、反应墒（RE）和ERPs。手术前或手术后数天测量指标的相关基础水平。结果基线、PASS-5分、RASS-4分、RASS-3至-1分和PASS-0分,对应的BIS值分别是94[4]（中位数,四分位数间距）、47[15]、68[9]、75[10]和88[6];对应的SE值分别是87[3]、46[10]、60[22]、74[21]和87[5];对应的RE值分别是97[4]、48[9]、71[25]、81[8]和96[3]（P〈0．05,Friedman检验）。BIS和墒都有高变异度。当单独考虑ERP振幅100时,各个镇静水平的ERPs值差异无显著性：但是、复括双参数主要变量分析的ERP辨别分析显示区别深度镇静、中度镇静和清醒状态的推算概率PK大约是0．89。与PK对应的RE,SE和BIS值分别是0．88、0．89和0．85。结论ERPs、BIS和熵均不能替代基于标准评分系统的临床镇静评估。全麻后对于极深镇静、深度到中度镇静和清醒的辨别,ERPs和脑电图仅能提供相似的PK值。BIS和熵存在较高的个体间和个体自身变异度,使其难以确定预测镇静水平的目标值范围,因而在危重患者中的使用受到限制。ERPs的变异度还不清楚。     

Time-frequency balanced spectral entropy as a measure of anesthetic drug effect in central nervous system during sevoflurane, propofol, and thiopental anesthesia

BACKGROUND: Time-frequency balanced spectral entropy of electroencephalogram (EEG) and frontal electromyogram (FEMG) is a novel measure of hypnosis during anesthesia. Two Entropy parameters are described: Response entropy (RE) is calculated from EEG and FEMG; and State Entropy (SE) is calculated mainly from EEG. This study was performed to validate their performance during transition from consciousness to unconsciousness under different anesthetic agents. METHODS: Response entropy, SE [S/5 Entropy Module, M-ENTROPY (later in text: Entropy), Datex-Ohmeda Division, Instrumentarium Corp., Helsinki, Finland] and BIS (BIS XP, A-2000, Aspect Medical Systems, Newton, MA) data were collected from 70 patients; 30 anesthetized with propofol 2 mg kg-1, 20 with sevoflurane inhalation, and 20 with thiopental 5 mg kg-1. Loss and regaining of consciousness (LOC, ROC) was tested every 10 s, and sensitivity, specificity, and prediction probability (Pk) were calculated. Behavior of the indices was studied. RESULTS: Sensitivity, specificity, and Pk values for consciousness were high and similar for all indices. During regaining of consciousness after propofol bolus, RE, SE, and BIS values recovered by 81 +/- 22%, 75 +/- 26%, and 59 +/- 18% (mean +/- SD), respectively, from the minimum relative to their baseline. After thiopental bolus, RE, SE, and BIS values recovered by 86+/-21%, 88 +/- 13%, and 63 +/- 14%, respectively. The relative rise was higher in RE and SE compared with BIS (P < 0.01). During deep levels of hypnosis, RE and SE decreased monotonously as a function of burst suppression ratio, while BIS showed biphasic behavior. On average, RE indicated emergence from anesthesia 11 s earlier than SE, and 12.4 s earlier than BIS. CONCLUSIONS: All indices, RE, SE, and BIS, distinguished excellently between conscious and unconscious states during propofol, sevoflurane, and thiopental anesthesia. During burst suppression, Entropy parameters RE and SE, but not BIS, behave monotonously. During regaining of consciousness after a thiopental or propofol bolus, RE and SE values recovered significantly closer to their baseline values than did BIS. Response entropy indicates emergence from anesthesia earlier than SE or BIS.     

Evaluation of the sedation level with propofol with electroencephalographic Entropy in comparison with bispectral index monitor

BACKGROUND: Entropy, a newly available electroencephalographic monitor, demonstrates two parameters, response entropy (RE) and state entropy (SE). The aim of this study is to compare RE and SE with bispectral index (BIS) during anesthetic induction with propofol. METHODS: Fifteen patients received target controlled infusion of propofol starting at 3 microg x ml(-1). We measured RE, SE and BIS and recorded effect-site concentrations of propofol at three sedation levels: VR1; conscious state before infusion of propofol, VR2; no response to verbal command, and VR3; no response to verbal command and shaking. Spearman rank correlations and prediction probability for sedation level were analyzed. RESULTS: Effect-site concentrations of propofol at VR1, VR2, and VR3 were 0, 1.8 +/- 0.7, and 2.4 +/- 0.7, respectively. All three parameters showed significant correlations with sedation levels. Prediction probability values of SE, RE, and BIS were 0.905, 0.894, and 0.890, respectively. CONCLUSIONS: Response entropy and SE can provide similar information as BIS about the sedation level with propofol.     

Spectral Entropy as a Measure of Hypnosis in Children

Background: The Datex-Ohmeda S/5 Entropy Module (Datex-Ohmeda Division, Instrumentarium Corp., Helsinki, Finland), using time-frequency balanced Spectral Entropy, is a novel tool for monitoring the hypnotic state during anesthesia. The Entropy Module produces two values, State Entropy (SE) and Response Entropy (RE), and in adults, it has been shown to measure reliably the hypnotic effects of various drugs. In children, Spectral Entropy has been only preliminary studied. The authors' aim was to study Spectral Entropy as a marker of hypnotic state during general anesthesia in infants and children.

Methods: Twenty infants (aged 1 month-1 yr) and 40 children (aged 1-15 yr) were anesthetized for surgery using standardized sevoflurane-nitrous oxide-based anesthesia. The relationships between SE, RE, or Bispectral Index (BIS) and (1) a modified Observer's Assessment of Alertness/Sedation Scale, (2) non-steady state end-tidal concentration of sevoflurane, (3) steady state end-tidal concentration of sevoflurane, and (4) hemodynamic values were calculated using prediction probability, nonlinear regression, and correlation coefficients, as appropriate. The performances of SE, RE, and BIS were compared.

Results: The prediction probability values (+/- SEM) of SE, RE, and BIS versus the modified Observer's Assessment of Alertness/Sedation Scale in the induction phase were 0.83 +/- 0.06, 0.88 +/- 0.06, and 0.87 +/- 0.08 for children and 0.76 +/- 0.08,0.79 +/- 0.08, and 0.73 +/- 0.10 for infants; values in the emergence phase were 0.68 +/- 0.05, 0.74 +/- 0.04, and 0.64 +/- 0.05 for children and 0.64 +/- 0.07, 0.69 +/- 0.06, and 0.72 +/- 0.06 for infants, respectively. SE, RE, and BIS values were inversely proportionally related to the end-tidal concentration of sevoflurane for children, but for infants, the correlation was much less clear. No significant correlations were found between SE, RE, or BIS values and the hemodynamic values.     

Spectral entropy as a measure of hypnosis in children

BACKGROUND: The Datex-Ohmeda S/5 Entropy Module (Datex-Ohmeda Division, Instrumentarium Corp., Helsinki, Finland), using time-frequency balanced Spectral Entropy, is a novel tool for monitoring the hypnotic state during anesthesia. The Entropy Module produces two values, State Entropy (SE) and Response Entropy (RE), and in adults, it has been shown to measure reliably the hypnotic effects of various drugs. In children, Spectral Entropy has been only preliminary studied. The authors' aim was to study Spectral Entropy as a marker of hypnotic state during general anesthesia in infants and children. METHODS: Twenty infants (aged 1 month-1 yr) and 40 children (aged 1-15 yr) were anesthetized for surgery using standardized sevoflurane-nitrous oxide-based anesthesia. The relationships between SE, RE, or Bispectral Index (BIS) and (1) a modified Observer's Assessment of Alertness/Sedation Scale, (2) non-steady state end-tidal concentration of sevoflurane, (3) steady state end-tidal concentration of sevoflurane, and (4) hemodynamic values were calculated using prediction probability, nonlinear regression, and correlation coefficients, as appropriate. The performances of SE, RE, and BIS were compared. RESULTS: The prediction probability values (+/- SEM) of SE, RE, and BIS versus the modified Observer's Assessment of Alertness/Sedation Scale in the induction phase were 0.83 +/- 0.06, 0.88 +/- 0.06, and 0.87 +/- 0.08 for children and 0.76 +/- 0.08,0.79 +/- 0.08, and 0.73 +/- 0.10 for infants; values in the emergence phase were 0.68 +/- 0.05, 0.74 +/- 0.04, and 0.64 +/- 0.05 for children and 0.64 +/- 0.07, 0.69 +/- 0.06, and 0.72 +/- 0.06 for infants, respectively. SE, RE, and BIS values were inversely proportionally related to the end-tidal concentration of sevoflurane for children, but for infants, the correlation was much less clear. No significant correlations were found between SE, RE, or BIS values and the hemodynamic values. CONCLUSIONS: Spectral Entropy may be a useful tool for measuring the level of hypnosis in anesthetized children and seems to perform as well as BIS. In infants, the clinical usefulness of both these electroencephalogram-derived methods must be evaluated in further controlled studies.     

Spectral entropy as an electroencephalographic measure of anesthetic drug effect: a comparison with bispectral index and processed midlatency auditory evoked response

BACKGROUND: The authors compared the behavior of two calculations of electroencephalographic spectral entropy, state entropy (SE) and response entropy (RE), with the A-Line ARX Index (AAI) and the Bispectral Index (BIS) and as measures of anesthetic drug effect. They compared the measures for baseline variability, burst suppression, and prediction probability. They also developed pharmacodynamic models relating SE, RE, AAI, and BIS to the calculated propofol effect-site concentration (Ceprop). METHODS: With institutional review board approval, the authors studied 10 patients. All patients received 50 mg/min propofol until either burst suppression greater than 80% or mean arterial pressure less than 50 mmHg was observed. SE, RE, AAI, and BIS were continuously recorded. Ceprop was calculated from the propofol infusion profile. Baseline variability, prediction of burst suppression, prediction probability, and Spearman rank correlation were calculated for SE, RE, AAI, and BIS. The relations between Ceprop and the electroencephalographic measures of drug effect were estimated using nonlinear mixed effect modeling. RESULTS: Baseline variability was lowest when using SE and RE. Burst suppression was most accurately detected by spectral entropy. Prediction probability and individualized Spearman rank correlation were highest for BIS and lowest for SE. Nonlinear mixed effect modeling generated reasonable models relating all four measures to Ceprop. CONCLUSIONS: Compared with BIS and AAI, both SE and RE seem to be useful electroencephalographic measures of anesthetic drug effect, with low baseline variability and accurate burst suppression prediction. The ability of the measures to predict Ceprop was best for BIS.     

Spectral Entropy as an Electroencephalographic Measure of Anesthetic Drug Effect: A Comparison with Bispectral Index and Processed Midlatency Auditory Evoked Response

Background: The authors compared the behavior of two calculations of electroencephalographic spectral entropy, state entropy (SE) and response entropy (RE), with the A-Line(R) ARX Index (AAI) and the Bispectral Index (BIS) and as measures of anesthetic drug effect. They compared the measures for baseline variability, burst suppression, and prediction probability. They also developed pharmacodynamic models relating SE, RE, AAI, and BIS to the calculated propofol effect-site concentration (Ceprop).

Methods: With institutional review board approval, the authors studied 10 patients. All patients received 50 mg/min propofol until either burst suppression greater than 80% or mean arterial pressure less than 50 mmHg was observed. SE, RE, AAI, and BIS were continuously recorded. Ceprop was calculated from the propofol infusion profile. Baseline variability, prediction of burst suppression, prediction probability, and Spearman rank correlation were calculated for SE, RE, AAI, and BIS. The relations between Ceprop and the electroencephalographic measures of drug effect were estimated using nonlinear mixed effect modeling.

Results: Baseline variability was lowest when using SE and RE. Burst suppression was most accurately detected by spectral entropy. Prediction probability and individualized Spearman rank correlation were highest for BIS and lowest for SE. Nonlinear mixed effect modeling generated reasonable models relating all four measures to Ceprop.     

Bispectral index and spectral entropy in neuroanesthesia

Spectral Entropy (SpEn) is an alternative tool to the bispectral index (BIS) for monitoring depth of hypnosis. SpEn measures response entropy (RE) and state entropy (SE). This open-label prospective study was designed to evaluate SpEn and BIS in 20 patients undergoing elective supratentorial neurosurgery with craniotomy and resection of brain tumors. SpEn and BIS were obtained continuously by Datex Ohmeda M-entropy module S/5 (Helsinki, Finland) and Aspect Medical System BIS (Newton), respectively. Total intravenous anesthesia was performed in all patients by Fresenius Vial infusion system (Brezins, France) to maintain a plasma concentration of propofol of 2.5 to 5 microg mL(-1) and sufentanil of 0.2 to 0.4 etag mL(-1). SpEn, BIS, the estimated propofol effect-site concentrations (Ce), the mean arterial pressure (MAP), and the heart rate (HR) were recorded during 12 specific events: induction of anesthesia, patient stop counting, loss of blinking reflex, intubation, mayfield pinning, craniotomy, termination of propofol infusion, recovery of blinking reflex, coughing, limb movement, order execution, and extubation. Stated that prediction probability or P(K) represents an indicator probability to predict correctly the rank order of an arbitrary pair of distinct observed indices of depth of hypnosis (ie, clinical settings and SpEn indices, or BIS, Ce, MAP, HR), PK of BIS, SE, RE, and Ce provided a better depth of hypnosis than MAP and HR; RE being the best for rapidity, SE for sensitivity, and BIS for specificity. There is good correlation between the 3 hypnosis indices and Ce. This study demonstrates that SpEn provides a reproducible hypnosis index for patients undergoing supratentorial neurosurgical procedures.     

Assessment of Depth of Anesthesia and Postoperative Respiratory Recovery after Remifentanil-versus Alfentanil-based Total Intravenous Anesthesia in Patients Undergoing Ear-Nose-Throat Surgery

Background: The authors investigated whether total intravenous anesthesia (TIVA) with precalculated equipotent infusion schemes for remifentanil and alfentanil would ensure appropriate analgesia and that remifentanil would result in better recovery characteristics.

Methods: Forty consenting patients (classified as American Society of Anesthesiologists physical status I-III) scheduled for microlaryngoscopy were randomized to receive, in a double-blind manner, either remifentanil (loading dose 1 [mu]g/kg; maintenance infusion, 0.25 [mu]g [middle dot] kg-1 [middle dot] min-1) or alfentanil (loading dose, 50 [mu]g/kg; maintenance infusion, 1 [mu]g [middle dot] kg-1 [middle dot] min-1) as the analgesic component of TIVA. They were combined with propofol (loading dose, 2 mg/kg; maintenance infusion, 100 [mu]g [middle dot] kg-1 [middle dot] min-1). To insure an equal state of anesthesia, the opioids were titrated to maintain heart rate and mean arterial pressure within 20% of baseline, and propofol was titrated to keep the bispectral index (BIS) less than 60. Neuromuscular blockade was achieved with succinylcholine. Drug dosages and the times from cessation of anesthesia to extubation, verbal response, recovery of ventilation, and neuropsychological testing, orientation, and discharge readiness were recorded.

Results: Demographics, duration of surgery, and anesthesia were similar between the two groups. Both groups received similar propofol doses. There were no difference in BIS values preoperatively (mean, 96), intraoperatively (mean, 55), and postoperatively (mean, 96). Recovery of BIS and times for verbal response did not differ. At 20, 30, and 40 min after terminating the opioid infusion, the peripheral oxygen saturation and respiratory rate were significantly higher in the remifentanil group compared with the alfentanil group.     

Racemic Ketamine Decreases Muscle Sympathetic Activity but Maintains the Neural Response to Hypotensive Challenges in Humans

Background: Cardiovascular stimulation and increased catecholamine plasma concentrations during ketamine anesthesia have been attributed to increased central sympathetic activity as well as catecholamine reuptake inhibition in various experimental models. However, direct recordings of efferent sympathetic nerve activity have not been performed in humans. The authors tested the hypothesis that racemic ketamine increases efferent muscle sympathetic activity (MSA) and maintains the muscle sympathetic response to hypotensive challenges.

Methods: Muscle sympathetic activity was recorded by microneurography in the peroneal nerve of six healthy subjects before and during anesthesia with racemic ketamine (2 mg/kg intravenously plus 30 [mu]g [middle dot] kg-1 [middle dot] min-1). Catecholamine plasma concentrations, heart rate, and blood pressure were also determined. Muscle sympathetic neural responses to a hypotensive challenge were assessed by injection of sodium nitroprusside (2-10 [mu]g/kg) before and during ketamine anesthesia. In the final step, increased arterial pressure observed during ketamine anesthesia was adjusted to preanesthetic baseline by sodium nitroprusside infusion (1-6 [mu]g [middle dot] kg-1 [middle dot] min-1).

Results: Ketamine significantly decreased MSA burst frequency (mean +/- SD, 18 +/- 9 bursts/min to 9 +/- 8 bursts/min) and burst incidence (26 +/- 11 bursts/100 heart beats to 9 +/- 6 bursts/100 heart beats). However, when increased mean arterial pressure (85 +/- 8 mmHg to 121 +/- 20 mmHg) was normalized to the awake baseline by sodium nitroprusside, MSA recovered (25 +/- 18 bursts/min; 23 +/- 14 bursts/100 heart beats). During ketamine anesthesia, both epinephrine (15 +/- 10 pg/ml to 256 +/- 193 pg/ml) and norepinephrine (250 +/- 105 pg/ml to 570 +/- 270 pg/ml) plasma concentrations significantly increased, as did heart rate (67 +/- 13 beats/min to 113 +/- 15 beats/min). Hypotensive challenges similarly increased MSA both in the awake state and during ketamine anesthesia.     

Narcotrend Monitoring Allows Faster Emergence and a Reduction of Drug Consumption in Propofol-Remifentanil Anesthesia

Background: The Narcotrend is a new electroencephalographic monitor designed to measure depth of anesthesia, based on a six-letter classification from A (awake) to F (increasing burst suppression) including 14 substages. This study was designed to investigate the impact of Narcotrend monitoring on recovery times and propofol consumption in comparison to Bispectral Index(R) (BIS(R)) monitoring or standard anesthetic practice.

Methods: With institutional review board approval and written informed consent, 120 adult patients scheduled to undergo minor orthopedic surgery were randomized to receive a propofol-remifentanil anesthetic controlled by Narcotrend, by BIS(R), or solely by clinical parameters. Anesthesia was induced with 0.4 [mu]g [middle dot] kg-1 [middle dot] min-1 remifentanil and a propofol target-controlled infusion at 3.5 [mu]g/ml. After intubation, remifentanil was reduced to 0.2 [mu]g [middle dot] kg-1 [middle dot] min-1, whereas the propofol infusion was adjusted according to clinical parameters or to the following target values: during maintenance to D0 (Narcotrend) or 50 (BIS(R)); 15 min before the end of surgery to C1 (Narcotrend) or 60 (BIS(R)). Recovery times were recorded by a blinded investigator, and average normalized propofol consumption was calculated from induction and maintenance doses.

Results: The groups were comparable for demographic data, duration of anesthesia, and mean remifentanil dosages. Compared with standard practice, patients with Narcotrend or BIS(R) monitoring needed significantly less propofol (standard practice, 6.8 +/- 1.2 mg [middle dot] kg-1 [middle dot] h-1vs. Narcotrend, 4.5 +/- 1.1 mg [middle dot] kg-1 [middle dot] h-1 or BIS(R), 4.8 +/- 1.0 mg [middle dot] kg-1 [middle dot] h-1;P < 0.001), opened their eyes earlier (9.3 +/- 5.2 vs. 3.4 +/- 2.2 or 3.5 +/- 2.9 min), and were extubated sooner (9.7 +/- 5.3 vs. 3.7 +/- 2.2 or 4.1 +/- 2.9 min).     

S (+)-Ketamine Increases Muscle Sympathetic Activity and Maintains the Neural Response to Hypotensive Challenges in Humans

Background: S (+)-Ketamine is reported to exert twofold greater analgesic and hypnotic effects but a shorter recovery time in comparison with racemic ketamine, indicating possible differential effects of stereoisomers. However, cardiovascular regulation during S (+)-ketamine anesthesia has not been studied. Muscle sympathetic activity (MSA) may be an indicator of the underlying alterations of sympathetic outflow. Whether S (+)-ketamine decreases MSA in a similar manner as the racemate is not known. Thus, the authors tested the hypothesis that S (+)-ketamine changes MSA and the muscle sympathetic response to a hypotensive challenge.

Methods: Muscle sympathetic activity was recorded by microneurography in the peroneal nerve of six healthy participants before and during anesthesia with S (+)-ketamine (670 [mu]g/kg intravenously followed by 15 [mu]g [middle dot] kg-1 [middle dot] min-1). Catecholamine and ketamine plasma concentrations, heart rate, and arterial blood pressure were also determined. MSA responses to a hypotensive challenge were assessed by injection of sodium nitroprusside (2-10 [mu]g/kg) before and during S (+)-ketamine anesthesia. In the final step, increased arterial pressure observed during anesthesia with S (+)-ketamine was adjusted to preanesthetic values by sodium nitroprusside infusion (1-6 [mu]g [middle dot] kg-1 [middle dot] min-1).

Results: Anesthesia with S (+)-ketamine (ketamine plasma concentration 713 +/- 295 [mu]g/l) significantly increased MSA burst frequency (mean +/- SD; 18 +/- 6 to 35 +/- 11 bursts/min) and burst incidence (32 +/- 10 to 48 +/- 15 bursts/100 heartbeats) and was associated with a doubling of norepinephrine plasma concentration (from 159 +/- 52 to 373 +/- 136 pg/ml) parallel to the increase in MSA. Heart rate and arterial blood pressure also significantly increased. When increased arterial pressure during S (+)-ketamine was decreased to awake values with sodium nitroprusside, MSA increased further (to 53 +/- 24 bursts/min and 60 +/- 20 bursts/100 heartbeats, respectively). The MSA increase in response to the hypotensive challenge was fully maintained during anesthesia with S (+)-ketamine.     

Comparative effects of ketamine on Bispectral Index and spectral entropy of the electroencephalogram under sevoflurane anaesthesia

Background. The Bispectral Index (BIS) and spectral entropyof the electroencephalogram can be used to assess the depthof hypnosis. Ketamine is known to increase BIS in anaesthetizedpatients and may confound that index as a guide to steer administrationof hypnotics. We compared the effects of ketamine on BIS, responseentropy (RE) and state entropy (SE) during surgery under sevofluraneanaesthesia. Methods. Twenty-two women undergoing gynaecological surgerywere enrolled in this double-blind, randomized study. Anaesthesiawas induced i.v. and maintained with sevoflurane. Under stablesurgical and anaesthetic conditions, patients were assignedto receive either a bolus of ketamine 0.5 mg kg^–1 or thesame volume of saline. Blood pressure, heart rate, BIS, RE andSE were measured every 2.5 min from 10 min before (baseline)until 15 min after ketamine or saline administration. The maximumrelative increase in BIS, RE and SE compared with baseline wascalculated for each patient. Values are mean (SD). Results. Baseline values were BIS 33 (4), RE 31 (5), SE 30 (5)for the ketamine patients and BIS 35 (3), RE 33 (5) and SE 32(6) for the patients receiving saline. BIS, RE and SE increasedsignificantly from 5 min (BIS) and 2.5 min (RE and SE) afterketamine administration, peaking at 46 (8) (BIS), 52 (12) (RE)and 50 (12) (SE) respectively. The maximum relative increasein RE [42.2 (10.4%)] and SE [41.6 (10.9)%] was higher than thatof BIS [29.4 (10.4%)]. Blood pressure, heart rate and RE–SEgradient did not change in either group. Conclusions. Ketamine administered under sevoflurane anaesthesiacauses a significant increase in BIS, RE and SE without modificationof the RE–SE gradient. This increase is paradoxical inthat it is associated with a deepening level of hypnosis.     

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.     

A comparison of bispectral index and entropy monitoring, in patients undergoing embolization of cerebral artery aneurysms after subarachnoid haemorrhage

Background. Processed EEG monitoring of anaesthetic depth couldbe useful in patients receiving general anaesthesia followingsubarachnoid haemorrhage. We conducted an observational studycomparing performance characteristics of bispectral index (BIS)and entropy monitoring systems in these patients. Methods. Thirty-one patients of the World Federation of Neurosurgeonsgrades 1 and 2, undergoing embolization of cerebral artery aneurysmsfollowing acute subarachnoid haemorrhage, were recruited tohave both BIS and entropy monitoring during general anaesthesia.BIS and entropy indices were matched to clinical indicatorsof anaesthetic depth. Anaesthetists were blinded to the anaestheticdepth monitoring indices. Analysis of data from monitoring devicesallowed calculation of prediction probability (P_K) constants,and receiver operating characteristic (ROC) analysis to be performed. Results. BIS and entropy [response entropy (RE), state entropy(SE)] performed well in their ability to show concordance withclinically observed anaesthetic depth. P_K values were generallyhigh (BIS 0.966–0.784, RE 0.934–0.663, SE 0.857–0.701)for both forms of monitoring. ROC curve analysis shows a highsensitivity and specificity for all monitoring indices whenused to detect the presence or absence of eyelash reflex. Areaunder curve for BIS, RE and SE to detect the absence or presenceof eyelash reflex was 0.932, 0.888 and 0.887, respectively.RE provides earlier warning of return of eyelash reflex thanBIS. Conclusion. BIS and entropy monitoring perform well in patientswho receive general anaesthesia after good grade subarachnoidhaemorrhage.