The arousal level of consciousness required for working memory performance: An anaesthesia study.

Regarding the stage of arousal level required for working memory to function properly, limited studies have been conducted on changes in working memory performance when the arousal level of consciousness decreases. This study aimed to experimentally clarify the stages of consciousness necessary for optimal working memory function. In this experiment, the sedation levels were changed step-by-step using anaesthesia, and the performance accuracy during the execution of working memory was assessed using a dual-task paradigm. Participants were required to categorize and remember words in a specific target category. Categorization performance was measured across four different sedative phases: before anaesthesia (baseline), and deep, moderate and light stages of sedation. Short-delay recognition tasks were performed under these four sedative stages, followed by long-delay recognition tasks after participants recovered from sedation. The results of the short-delay recognition task showed that the performance was lowest at the deep stage. The performance of the moderate stage was lower than the baseline. In the long-delay recognition task, the performance under moderate sedation was lower than that under baseline and light sedation. In addition, the performance under light sedation was lower than that under baseline. These results suggest that task performance becomes difficult under half sedation and that transferring information to long-term memory is difficult even under one-quarter sedation.

Decrease of the peak heights of EEG bicoherence indicated insufficiency of analgesia during surgery under general anesthesia.

BACKGROUND: Studies show that the two peak heights of electroencephalographic bicoherence (pBIC-high, pBIC-low) decrease after incision and are restored by fentanyl administration. We investigated whether pBICs are good indicators for adequacy of analgesia during surgery. METHODS: After local ethical committee approval, we enrolled 50 patients (27-65 years, ASA-PS I or II) who were scheduled elective surgery. Besides standard anesthesia monitors, to assess pBICs, we used a BIS monitor and freeware Bispectrum Analyzer for A2000. Fentanyl 5 µg/kg was completely administered before incision, and anesthesia was maintained with sevoflurane. After skin incision, when the peak of pBIC-high or pBIC-low decreased by 10% in absolute value (named LT10-high and LT10-low groups in order) or when either peak decreased to below 20% (BL20-high and BL20-low groups), an additional 1 g/kg of fentanyl was administered to examine its effect on the peak that showed a decrease. RESULTS: The mean values and standard deviation for pBIC-high 5 min before fentanyl administration, at the time of fentanyl administration, and 5 min after fentanyl administration for LT10-high group were 39.8% (10.9%), 26.9% (10.5%), and 35.7% (12.5%). And those for pBIC-low for LT10-low group were 39.5% (6.0%), 26.8% (6.4%) and 35.0% (7.0%). Those for pBIC-high for BL20-high group were 26.3% (5.6%), 16.5% (2.6%), and 25.7% (7.0%). And those for pBIC-low for BL20-low group were 26.7% (4.8%), 17.4% (1.8%) and 26.9% (5.7%), respectively. Meanwhile, at these trigger points, hemodynamic parameters didn't show significant changes. CONCLUSION: Superior to standard anesthesia monitoring, pBICs are better indicators of analgesia during surgery. TRIAL REGISTRY: Clinical trial Number and registry URL: UMIN ID: UMIN000042843 https://center6.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno = R000048907.

Effect of remifentanil on three effect-site concentrations of propofol and their relationship during electroencephalography at loss of response, at maximum alpha power, and at onset of burst suppression: a prospective randomized trial.

PURPOSE: The effect-site concentration (Ce) at loss of response (Ce-LOR) to propofol closely correlates both with Ce as electroencephalographic alpha power becomes highest (Ce-alpha) and with Ce at onset of burst suppression (BS) (Ce-OBS), when no opioids are administered. Co-administration of opioids dose-dependently decreases Ce-LOR. We investigated the influence of remifentanil on the relationship between these three Ces. METHODS: After receiving approval from our local ethical committee, with written informed consent, we enrolled 90 participants (ASA-PS I or II) who were scheduled for elective surgery. Participants were randomly assigned to three groups: constant remifentanil Ce 0 ng/ml (Remi_0); 1 ng/mL (Remi_1); and 2 ng/mL (Remi_2). We recorded both raw EEG and EEG-derived parameters on a computer. After reaching remifentanil equilibrium, we administered propofol using a target-controlled infusion pump such that propofol Ce increased to about 0.3 µg/mL/min. After determining Ce-LOR, we administered 0.6 mg/kg of rocuronium and started mask ventilation. The study protocol ended after observation of BS. RESULTS: Three participants were excluded. Ce-LOR in each group (Remi_0, Remi_1, Remi_2) was 2.00 ± 0.58 µg/mL, 1.43 ± 0.49 µg/mL, and 1.37 ± 0.42 µg/mL. Ce-alpha was 2.91 ± 0.63 µg/mL, 2.30 ± 0.41 µg/mL, and 2.12 ± 0.39 µg/mL. Ce-OBS was 3.80 ± 0.69 µg/mL, 3.25 ± 0.68 µg/mL, and 2.90 ± 0.57 µg/mL. In three other instances, Ce was decreased by remifentanil. Generalized linear model analysis revealed that remifentanil had no influence on the relationship between the three Ces. CONCLUSION: During propofol anesthesia, even low concentrations of remifentanil shifted concentration-related electroencephalographic changes.

What are standard monitoring devices for anesthesia in future?

Monitoring the patient's physiological functions is critical in clinical anesthesia. The latest version of the Japanese Society of Anesthesiologists' Guidelines for Safe Anesthesia Monitoring, revised in 2019, covers various factors, including electroencephalogram monitoring, oxygenation, ventilation, circulation, and muscle relaxation. However, with recent advances in monitoring technologies, the information provided has become more detailed, requiring practitioners to update their knowledge. At a symposium organized by the Journal of Anesthesia in 2023, experts across five fields discussed their respective topics: anesthesiologists need to interpret not only the values displayed on processed electroencephalogram monitors but also raw electroencephalogram data in the foreseeable future. In addition to the traditional concern of preventing hypoxemia, monitoring for potential hyperoxemia and the effects of mechanical ventilation itself will become increasingly important. The importance of using AI analytics to predict hypotension, assess nociception, and evaluate microcirculation may increase. With the recent increase in the availability of neuromuscular monitoring devices in Japan, it is important for anesthesiologists to become thoroughly familiar with the features of each device to ensure its effective use. There is a growing desire to develop and introduce a well-organized, integrated "single screen" monitor.

The surgical Apgar score predicts postoperative complications and the survival in lung cancer patients.

PURPOSE: The surgical Apgar score (SAS)-calculated using the intraoperative variables estimated blood loss, lowest heart rate, and lowest mean systolic pressure-is associated with mortality in cancer surgery. We investigated the utility of the SAS in patients with lung cancer undergoing surgery. METHODS: We retrospectively analyzed the data of 691 patients who underwent surgery for primary lung cancer between 2015 and 2019 in a single institute and analyzed the impact of the SAS. RESULTS: Of the 691 patients, 138 (20%), 57 (8.2%), and 7 (1.0%) had postoperative complications of all grades, grades ≥ III, and grade V, respectively, according to the Clavien-Dindo classification. The C-index for postoperative complications of grades ≥ III was 0.605. A lower score (0-5 points) (odds ratio 3.09 against 8-10 points, P = 0.04) and a lower percentage of vital capacity (odds ratio 0.97, P = 0.04) were independent negative risk factors for major postoperative complications. Patients with a lower score (0-5 points) had poor 5-year overall and cancer-specific survival rates (60.1% and 72.3%, respectively; P < 0.05 for both). CONCLUSIONS: The surgical Apgar score predicted postoperative complications and the long-term survival. Surgeons may improve surgical results using the SAS.

Equilibration rate constant, ke0, to determine effect-site concentration for the Masui remimazolam population pharmacokinetic model in general anesthesia patients.

Effect-site concentration is widely used to determine drug dosage in anesthesia practice. To obtain effect-site concentration, a pharmacokinetic model with a corresponding equilibration rate constant between plasma and effect-site, ke0, is necessary. Remimazolam, a novel short-acting benzodiazepine, has been approved as anesthetic/sedative. Recently, a remimazolam pharmacokinetic model has been published using a large dataset including wide range of subject characteristics (416 males and 246 females, age 18-93 years, total body weight 34-149 kg, height 133-204 cm, body mass index 14-61 kg m-2, ASA physical status: I-IV, and Asian, White, American African, and 2 other races). This Masui model can be applicable to various patients, but a pharmacodynamic model including ke0 was not developed simultaneously. A previous article has indicated that the time to peak effect of drug after its bolus should be used to determine ke0 for a pharmacokinetic model without simultaneous development of corresponding pharmacodynamic model. The ke0 value can be calculated using numerical analysis but not algebraic solution. We provide the detail method of the numerical analysis and a tool to have ke0 value easily for the Masui remimazolam PK model. Additionally, we provide a multiple regression model to have ke0 value for the PK model.

Use of Multiple EEG Features and Artificial Neural Network to Monitor the Depth of Anesthesia.

The electroencephalogram (EEG) can reflect brain activity and contains abundant information of different anesthetic states of the brain. It has been widely used for monitoring depth of anesthesia (DoA). In this study, we propose a method that combines multiple EEG-based features with artificial neural network (ANN) to assess the DoA. Multiple EEG-based features can express the states of the brain more comprehensively during anesthesia. First, four parameters including permutation entropy, 95% spectral edge frequency, BetaRatio and SynchFastSlow were extracted from the EEG signal. Then, the four parameters were set as the inputs to an ANN which used bispectral index (BIS) as the reference output. 16 patient datasets during propofol anesthesia were used to evaluate this method. The results indicated that the accuracies of detecting each state were 86.4% (awake), 73.6% (light anesthesia), 84.4% (general anesthesia), and 14% (deep anesthesia). The correlation coefficient between BIS and the index of this method was 0.892 ( p < 0.001 ). The results showed that the proposed method could well distinguish between awake and other anesthesia states. This method is promising and feasible for a monitoring system to assess the DoA.

Individual indicators of appropriate hypnotic level during propofol anesthesia: highest alpha power and effect-site concentrations of propofol at loss of response.

BACKGROUND: Electroencephalogram (EEG) waveforms vary widely among individuals, this decreases the usefulness of BIS™ monitors for assessing the effects of propofol. Practically, anesthesia is only seen as too deep when evidence of burst-suppression is seen. We designed an experiment to help towards better assessment of individual anesthetic needs. First, to mark the Ce (effect-site concentration) of propofol at loss of response to calling name and gently shaking shoulders (LOR), we defined Ce-LOR. To mark the transient power increase in the alpha range (9-14 Hz), common to all patients, when propofol concentration gradually increases, we defined Ce-alpha as the highest recorded alpha power for Ce. We also defined Ce-OBS as the Ce of propofol at initial observation of burst-suppression. Then we tried to predict Ce-LOR and Ce-alpha from Ce-OBS, vice versa, and considered the significance of these parameters. METHODS: We enrolled 26 female patients (age 33-65) who were undergoing scheduled mastectomy. During anesthesia, we recorded all raw EEG packets as well as EEG-derived parameters on a computer from BIS-XP™ monitor. Propofol was infused using a TCI pump. Target concentration was adjusted so that Ce of propofol was gradually increased. RESULTS: We obtained the following regression equation; Ce-alpha or Ce-OBS = Ce-LOR × 0.87 + 1.06 + dummy × 0.83 (for Ce-alpha dummy = 0, and for Ce-OBS = 1; adjusted r = 0.90, p < 2.2e-16) by ANCOVA. At Ce-alpha, BIS was 50.2 ± 7.7. CONCLUSION: Ce-alpha and Ce-OBS could be estimated from Ce-LOR. Based on Ce-LOR it is possible to manage the hypnotic level of individual patients.

Sensory cognitive abnormalities of pain in autism spectrum disorder: a case-control study.

BACKGROUND: The Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) recently included sensory processing abnormalities in the diagnostic criteria for individuals with autism spectrum disorder (ASD). However, there is no standard method for evaluating sensory abnormalities in individuals with ASD. METHODS: Fifteen individuals with ASD and 15 age- and sex-matched controls were enrolled in this study. We compared objective pain sensitivity by measuring the pain detection threshold and pain tolerance to three different stimuli (electricity, heat, and cold). Then, we compared both subjective pain sensitivity, assessed by the visual analog scale (VAS), and quality of pain, assessed by the short-form McGill Pain Questionnaire (SF-MPQ), to determine the maximum tolerable pain intensities of each stimulation. RESULTS: The pain detection threshold and pain tolerance of individuals with ASD were not impaired, indicating that there were no differences in the somatic perception of pain between groups. However, individuals with ASD were hyposensitive to subjective pain intensity compared to controls (VAS; electrical: p = 0.044, cold: p = 0.011, heat: p = 0.042) and hyposensitive to affective aspects of pain sensitivity (SF-MPQ; electrical: p = 0.0071, cold: p = 0.042). CONCLUSIONS: Our results suggest that the cognitive pathways for pain processing are impaired in ASD and, furthermore, that our methodology can be used to assess pain sensitivity in individuals with ASD. Further investigations into sensory abnormalities in individuals with ASD are needed to clarify the pathophysiologic processes that may alter sensory processing in this disorder.

Rethinking general anesthesia for cesarean section.

In this review, we describe the current consensus surrounding general anesthetic management for cesarean section. For induction of anesthesia, rapid-sequence induction using thiopental and suxamethonium has been the recommended standard for a long time. In recent years, induction of anesthesia using propofol, rocuronium, and remifentanil have been gaining popularity. To prevent aspiration pneumonia, a prolonged preoperative fasting and an application of cricoid pressure during induction of anesthesia have been recommended, but these practices may require revision. Guidelines for difficult airway management were developed first in obstetric anesthesia, and the use of a supraglottic airway is now recognized as an effective rescue device. After the delivery of a fetus, switching from volatile anesthetics to intravenous anesthetics has been recommended to avoid uterine atony. At the same time, intraoperative awareness should be avoided. The rate of persistent wound pain is higher when only general anesthesia was used during cesarean section than with regional anesthesia, and thus it is necessary to provide a sufficient postoperative analgesia using multimodal analgesia, including intravenous patient-controlled analgesia (IV-PCA), transversus abdominis plane (TAP) block, non-steroidal inflammatory drugs, and acetaminophen.

In vitro and in vivo effects of hemodilution on kaolin-based activated clotting time predicted heparin requirement using a heparin dose-response technique.

PURPOSE: The heparin dose-response (HDR) technique is based on activated clotting time (ACT) response to a fixed-dose heparin bolus, which varies substantially among patients. It is unclear, however, whether hemodilution-associated reductions in coagulation and anticoagulation factors affect the HDR slope. METHODS: For in vitro hemodilution, aliquots of whole blood from healthy volunteers were diluted 9:1 and 8:2 v/v with normal saline. For in vivo hemodilution, a prospective observational study was performed on 46 patients who underwent elective cardiovascular surgery with or without cardiopulmonary bypass. HDR slope, antithrombin (AT) activity, complete blood count, and other coagulation parameters were compared after induction of anesthesia and after hemodilution with 500 ml of intravenous fluid. RESULTS: In vitro 10 and 20 % hemodilution significantly increased the HDR slope relative to baseline, reducing the heparin requirement. Hemodilution of heparinized samples significantly prolonged ACT, whereas there was no significant change in non-heparinized blood. The percent changes in fibrinogen and AT activity were significantly greater at 20 % than those of the other coagulation variables. In vivo, hemodilution significantly increased the HDR slope and reduced heparin requirement. The percent change in fibrinogen due to hemodilution was significantly greater than the change in AT activity. Target ACTs of 300 and 450 s were not achieved in 83.3 and 53.8 % of patients, respectively. CONCLUSION: In vitro and in vivo hemodilution significantly increased the HDR slope and reduced the requirement for heparin. In vitro, the HDR slope did not change in parallel but became steeper, depending on the degree of hemodilution.

[Preoperative Management of Patients with Bronchial Asthma or Chronic Bronchitis].

Bronchial asthma is characterized by chronic airway inflammation. The primary goal of treatment of asthma is to maintain the state of control. According to the Japanese guidelines (JGL2012), long-term management consists of 4 therapeutic steps, and use of inhaled corticosteroids (ICS) is recommended at all 4 steps. Besides ICS, inhalation of long-acting ß2-agonist (LABA) is also effective. Recently, omalizumab (a humanized antihuman IgE antibody) can be available for patients with severe allergic asthma. Although there is no specific strategy for preoperative treatment of patients with asthma, preoperative systemic steroid administration seemed to be effective to prevent asthma attack during anesthesia. The most common cause of chronic bronchitis is smoking. Even the respiratory function is within normal limits, perioperative management of patients with chronic bronchitis is often troublesome. The most common problem is their sputum. To minimize perioperative pulmonary complication in these patients, smoking cessation and pulmonary rehabilitation are essential. It is known that more than 1 month of smoking cessation is required to reduce perioperative respiratory complication. However, even one or two weeks of smoking cessation can decrease sputum secretion. In summary, preoperative optimization is most important to prevent respiratory complication in patients with bronchial asthma or chronic bronchitis.

Parameter selection in permutation entropy for an electroencephalographic measure of isoflurane anesthetic drug effect.

The permutation entropy (PE) of the electroencephalographic (EEG) signals has been proposed as a robust measure of anesthetic drug effect. The calculation of PE involves the somewhat arbitrary selection of embedding dimension (m) and lag (τ) parameters. Previous studies of PE include the analysis of EEG signals under sevoflurane or propofol anesthesia, where different parameter settings were determined using a number of different criteria. In this study we choose parameter values based on the quantitative performance, to quantify the effect of a wide range of concentrations of isoflurane on the EEG. We analyzed a set of previously published EEG data, obtained from 29 patients who underwent elective abdominal surgery under isoflurane general anesthesia combined with epidural anesthesia. PE indices using a range of different parameter settings (m = 3-7, τ = 1-5) were calculated. These indices were evaluated as regards: the correlation coefficient (r) with isoflurane end-tidal concentration, the relationship with isoflurane effect-site concentration assessed by the coefficient of determination (R (2)) of the pharmacokinetic-pharmacodynamic models, and the prediction probability (PK). The embedding dimension (m) and lag (τ) have significant effect on the r values (Two-way repeated-measures ANOVA, p < 0.001). The proposed new permutation entropy index (NPEI) [a combination of PE(m = 3, τ = 2) and PE(m = 3, τ = 3)] performed best among all the parameter combinations, with r = 0.89(0.83-0.94), R (2) = 0.82(0.76-0.87), and PK = 0.80 (0.76-0.85). Further comparison with previously suggested PE measures, as well as other unrelated EEG measures, indicates the superiority of the NPEI. The PE can be utilized to indicate the dynamical changes of EEG signals under isoflurane anesthesia. In this study, the NPEI measure that combines the PE with m = 3, τ = 2 and that with m = 3, τ = 3 is optimal.

The pulmonary surgical Apgar score for lung cancer surgery predicts postoperative complications and long-term survival.

OBJECTIVES: The surgical Apgar score, calculated using 3 intraoperative variables (blood loss, lowest mean arterial pressure and lowest heart rate), is associated with mortality in cancer surgery. The original score has less applicability in lung cancer surgery; therefore, we innovated the modified pulmonary surgical Apgar score with additional intraoperative oxygen saturation representing pulmonary parenchymal damage and cardiopulmonary dynamics. METHODS: We retrospectively analysed the data of 691 patients who underwent surgery for primary lung cancer between 2015 and 2019 at a single institute. We analysed the utility of the pulmonary surgical Apgar score compared with the original surgical Apgar score. RESULTS: Postoperative complications were observed in 57 (8.2%) and 7 (1.0%) of the 691 patients who were stratified as grade ≥III and V, respectively, according to the Clavien-Dindo classification. We compared the fitness of the score in predicting postoperative complications; the calculated c-index (0.622) was slightly higher than the original c-index (0.604; P = 0.398). Patients were categorized into 3 groups based on their scores as follows: 0-6 points (n = 59), 7-9 points (n = 420) and 10-12 points (n = 212). Univariable and multivariable analyses demonstrated that a lower score was an independent negative risk factor for postoperative complications (odds ratio 3.53; P = 0.02). Patients with lower scores had a considerably poor 5-year overall survival (64.6%) (P = 0.07). CONCLUSIONS: The pulmonary surgical Apgar score predicts postoperative complications and long-term survival in patients with lung cancer undergoing surgery and may be utilized for postoperative management.

The impact of nitrous oxide on electroencephalographic bicoherence during isoflurane anesthesia.

BACKGROUND: We previously reported that electroencephalographic (EEG) bicoherence, the degree of phase coupling among the frequency components of a signal, showed 2 peaks during isoflurane anesthesia. Hayashi et al. (Br J Anaesth 2007;99:389-95) also revealed that the peak frequency of bicoherence around 10 Hz increased when ketamine was added. Because nitrous oxide (N(2)O) and ketamine share several common features, they are often treated as the same category of anesthetic. Here, we investigated the effect of N(2)O on EEG bicoherence and other EEG derivatives during isoflurane anesthesia. METHODS: Twenty patients (aged 34-72 years, ASA physical status I and II) of either gender who underwent elective laparoscopic surgery were included. Raw EEG data, along with EEG-derived parameters, were recorded using an A-1050 Bispectral Index (BIS) monitor and our self-authored Bispectral Analyzer for BIS software. We compared 2 peaks of EEG bicoherence (pBIC-low, around 4 Hz; and pBIC-high, around 10 Hz), as well as BIS and spectral edge frequency 95% (SEF95). Anesthesia was induced with 3 mg · kg(-1) thiopental and 3 µg · kg(-1) fentanyl. After tracheal intubation, anesthesia was maintained with isoflurane (expired concentration at 1.0%), oxygen, and nitrogen. Fentanyl was added and maintained at an estimated effect-site concentration of >1.5 ng · mL(-1). We obtained baseline data 1 hour after induction of anesthesia, then 70% N(2)O was added for 30 minutes. RESULTS: Before N(2)O, pBIC-low and pBIC-high were 49.3% ± 8.3% and 42.4% ± 11.0%. Ten minutes after starting N(2)O, pBIC-high decreased to 14.9% ± 5.9% (P < 0.001), and it was statistically significantly lower throughout the N(2)O period. Meanwhile, pBIC-low transiently decreased to 37.2% ± 12.8% (P = 0.01) during the early phase of N(2)O administration. Before N(2)O, BIS and SEF95 were 43.2 ± 4.9 and 13.1 ± 2.0 Hz, respectively. Both BIS and SEF95 slightly but statistically significantly decreased during N(2)O administration. Fifteen minutes after starting N(2)O, BIS and SEF95 were 35.7 ± 6.2 (P < 0.001) and 8.6 ± 1.8 Hz (P < 0.001) and they decreased more when large δ waves emerged. Fifteen minutes after stopping N(2)O, BIS, SEF95, as well as pBIC-low and pBIC-high returned to pre-N(2)O values. CONCLUSION: Dissimilar to the effect of ketamine, N(2)O significantly decreases pBIC-high during isoflurane anesthesia.

Pentazocine increases bispectral index without surgical stimulation during nitrous oxide-sevoflurane anesthesia.

Although there have been a large number of reports on the effects of opioids on the bispectral index (BIS) during anesthesia, the effects of pentazocine on the BIS have not been reported. In this study, 60 patients scheduled for elective oral surgery [30 females, 30 males; all American Society of Anesthesiologists Physical Status (ASA PS) category 1] were enrolled in the trials. Maintaining gender parity, we randomly assigned the patients to one of three groups: pentazocine group (0.3 mg/kg; n = 20), fentanyl group (1 µg/kg; n = 20), or saline group (n = 20); these opioids were administered intravenously 15 min after the intubation. Anesthesia was induced with thiopental and vecuronium bromide and maintained with nitrous oxide (4 l/min)-oxygen (2 l/min)-sevoflurane (1%). At 15 min after the intubation, mean arterial blood pressure (MAP), heart rate (HR), and BIS index were recorded as baseline values. MAP, HR, and BIS values were measured at 2.5-min after the intubation up to 30 min. All data were expressed as the mean ± standard deviation. Differences in BIS values, MAP, and HR among the three groups throughout the experiment were analyzed using two-way repeated-measures analysis of variance (ANOVA), and demographic data among the three groups were analyzed using one-way ANOVA. Post hoc comparisons were performed using Fisher's protected least significant difference test. A P value of <0.05 was considered to indicate statistically significance. MAP and HR showed no significant differences among the three groups during the study. BIS values significantly increased between 5 and 15 min after the intubation relative to the baseline value in the pentazocine group (P < 0.001), and BIS values in this group were significantly during this time period than those in the fentanyl and saline group (P < 0.001). BIS values were not significantly different between the fentanyl group and saline group. These results indicated that pentazocine, but not fentanyl, under nitrous oxide-sevoflurane anesthesia caused a statistically significant increase in BIS in our patients.

[Mechanism of anesthesia: view from the EEG during anesthesia].

It is widely known that electroencephalogram (EEG) shows dramatic changes with increase of the concentration of anesthetic. It is considered that volatile anesthetics (i. e. isoflurane, sevoflurane), barbiturates, propofol show anesthetic effect by potentiating GABAA receptor. Changing patterns of EEG by these anesthetics are quite similar. In light anesthetic level, high frequency with low amplitude waves are dominant. With increase of anesthetic concentration, waves in alpha range (8-13 Hz) become dominant. In deeper levels, powers in alpha range then become smaller and theta or delta powers become dominant. With further deeper levels, EEG waveform changes into specific pattern so-called "burst and suppression", and finally it becomes flat. The author considers that prominent alpha power indicates adequate anesthetic level. However this is not always the required condition for adequate anesthesia, because alpha power never becomes larger in some patients even when the anesthetic level was judged as adequate by concentration dependent changing patterns of EEG. As EEG changes in relation to the concentration of anesthetic, it seems to be correlated with the level of consciousness. But EEG patterns during anesthesia are mainly determined by the condition of thalamic neurons, and it would merely indicate the level of hypnosis indirectly.

Pregnancy does not enhance volatile anesthetic sensitivity on the brain: an electroencephalographic analysis study.

BACKGROUNDS: Parturients are thought to be more sensitive to inhalational anesthetics because their minimum alveolar concentration is decreased. However, this conventional theory may be wrong, because, according to recent animal studies, minimum alveolar concentration indicates anesthetic effect on the spinal cord but not on the brain. The aim of this electroencephalographic study was to investigate the differences in the hypnotic effect of sevoflurane on parturients and nonpregnant patients. METHODS: Fifteen parturients undergoing cesarean section and 15 patients undergoing elective gynecologic surgery were enrolled. Anesthesia was induced with 4 mg/kg thiopental, 2 microg/kg fentanyl, and 2 mg/kg suxamethonium or 0.15 mg/kg vecuronium. Anesthesia was maintained with sevoflurane and fentanyl. The electroencephalographic signals, obtained from the bispectral index monitor, were recorded on a computer. We calculated 95% spectral edge frequency, amplitude, and bicoherence using custom software (Bispectrum Analyzer for bispectral index). After confirming that end-tidal sevoflurane had reached equilibrium, we measured electroencephalographic parameters of sevoflurane at 2.0 and 1.5% during surgery and at 1.0 and 0.5% after surgery. RESULTS: With the decrease of end-tidal sevoflurane concentration from 2.0 to 0.5%, 95% spectral edge frequency, amplitude, bispectral index, and bicoherence values changed dose-dependently in pregnant and nonpregnant women (P<0.0001). However, there were no significant differences in those electroencephalographic parameters in pregnant and nonpregnant women. CONCLUSIONS: This electroencephalographic study has shown that pregnancy does not enhance hypnotic effect of sevoflurane. These results suggested that the decrease in minimum alveolar concentration during pregnancy does not mean an enhanced volatile anesthetic effect on the brain.

Predominant effects of midazolam for conscious sedation: benefits beyond the early postoperative period.

PURPOSE: Conscious sedation with intravenous sedative-hypnotic drugs has the advantage of relaxing patients before invasive procedures. Preoperative anxiety has been suggested to correlate with postoperative comfortableness. In this study, we chose midazolam and droperidol as well-established intravenous sedative-hypnotic drugs. We evaluated the preoperative anxiolytic effect on postoperative memories and emotions up to the first postoperative morning. METHODS: In a prospective, double blind study, 120 patients requiring epidural anesthesia were randomly assigned to one of three groups to receive saline, midazolam (0.04 mg/kg), or droperidol (0.1 mg/kg). Cardiovascular and respiratory measurements, observer's assessment of alertness/sedation scale, level of anxiety and discomfort of the patients, pain during the infiltration of local anesthetics, and incidence of adverse effects were recorded. Amnesia, anxiety, and discomfort during the epidural procedure were re-assessed between 12 and 20 h postsurgery. RESULTS: Patients who received sedatives were significantly more sedated (P < 0.0001), but the pain score was significantly higher in the droperidol group (P = 0.0007) at epidural catheterization. On the first postoperative morning, patients receiving midazolam had a significantly lower pain score (P < 0.0001) with less anxiety and discomfort. Patients in both the midazolam and droperidol groups showed a significant decrease in blood pressure (P < 0.0167), but no respiratory impairment. No adverse effects were experienced throughout the study period. CONCLUSION: Conscious sedation with intravenous midazolam 0.04 mg/kg significantly decreased the anxiety and discomfort scores of the patients on the day following surgery but had no effect on these immediately following the epidural catheterization procedure.