Substance specific EEG patterns in mice undergoing slow anesthesia induction.

The exact mechanisms and the neural circuits involved in anesthesia induced unconsciousness are still not fully understood. To elucidate them valid animal models are necessary. Since the most commonly used species in neuroscience are mice, we established a murine model for commonly used anesthetics/sedatives and evaluated the epidural electroencephalographic (EEG) patterns during slow anesthesia induction and emergence. Forty-four mice underwent surgery in which we inserted a central venous catheter and implanted nine intracranial electrodes above the prefrontal, motor, sensory, and visual cortex. After at least one week of recovery, mice were anesthetized either by inhalational sevoflurane or intravenous propofol, ketamine, or dexmedetomidine. We evaluated the loss and return of righting reflex (LORR/RORR) and recorded the electrocorticogram. For spectral analysis we focused on the prefrontal and visual cortex. In addition to analyzing the power spectral density at specific time points we evaluated the changes in the spectral power distribution longitudinally. The median time to LORR after start anesthesia ranged from 1080 [1st quartile: 960; 3rd quartile: 1080]s under sevoflurane anesthesia to 1541 [1455; 1890]s with ketamine. Around LORR sevoflurane as well as propofol induced a decrease in the theta/alpha band and an increase in the beta/gamma band. Dexmedetomidine infusion resulted in a shift towards lower frequencies with an increase in the delta range. Ketamine induced stronger activity in the higher frequencies. Our results showed substance-specific changes in EEG patterns during slow anesthesia induction. These patterns were partially identical to previous observations in humans, but also included significant differences, especially in the low frequencies. Our study emphasizes strengths and limitations of murine models in neuroscience and provides an important basis for future studies investigating complex neurophysiological mechanisms.

Electroencephalographic guided propofol-remifentanil TCI anesthesia with and without dexmedetomidine in a geriatric population: electroencephalographic signatures and clinical evaluation.

Elderly and multimorbid patients are at high risk for developing unfavorable postoperative neurocognitive outcomes; however, well-adjusted and EEG-guided anesthesia may help titrate anesthesia and improve postoperative outcomes. Over the last decade, dexmedetomidine has been increasingly used as an adjunct in the perioperative setting. Its synergistic effect with propofol decreases the dose of propofol needed to induce and maintain general anesthesia. In this pilot study, we evaluate two highly standardized anesthetic regimens for their potential to prevent burst suppression and postoperative neurocognitive dysfunction in a high-risk population. Prospective, randomized clinical trial with non-blinded intervention. Operating room and post anesthesia care unit at Hospital Base San José, Osorno/Universidad Austral, Valdivia, Chile. 23 patients with scheduled non-neurologic, non-cardiac surgeries with age > 69 years and a planned intervention time > 60 min. Patients were randomly assigned to receive either a propofol-remifentanil based anesthesia or an anesthetic regimen with dexmedetomidine-propofol-remifentanil. All patients underwent a slow titrated induction, followed by a target controlled infusion (TCI) of propofol and remifentanil (n = 10) or propofol, remifentanil and continuous dexmedetomidine infusion (n = 13). We compared the perioperative EEG signatures, drug-induced changes, and neurocognitive outcomes between two anesthetic regimens in geriatric patients. We conducted a pre- and postoperative Montreal Cognitive Assessment (MoCa) test and measured the level of alertness postoperatively using a sedation agitation scale to assess neurocognitive status. During slow induction, maintenance, and emergence, burst suppression was not observed in either group; however, EEG signatures differed significantly between the two groups. In general, EEG activity in the propofol group was dominated by faster rhythms than in the dexmedetomidine group. Time to responsiveness was not significantly different between the two groups (p = 0.352). Finally, no significant differences were found in postoperative cognitive outcomes evaluated by the MoCa test nor sedation agitation scale up to one hour after extubation. This pilot study demonstrates that the two proposed anesthetic regimens can be safely used to slowly induce anesthesia and avoid EEG burst suppression patterns. Despite the patients being elderly and at high risk, we did not observe postoperative neurocognitive deficits. The reduced alpha power in the dexmedetomidine-treated group was not associated with adverse neurocognitive outcomes.

Connected consciousness after tracheal intubation in young adults: an international multicentre cohort study.

BACKGROUND: Connected consciousness, assessed by response to command, occurs in at least 5% of general anaesthetic procedures and perhaps more often in young people. Our primary objective was to establish the incidence of connected consciousness after tracheal intubation in young people aged 18-40 yr. The secondary objectives were to assess the nature of these responses, identify relevant risk factors, and determine their relationship to postoperative outcomes. METHODS: This was an international, multicentre prospective cohort study using the isolated forearm technique to assess connected consciousness shortly after tracheal intubation. RESULTS: Of 344 enrolled subjects, 338 completed the study (mean age, 30 [standard deviation, 6.3] yr; 232 [69%] female). Responses after intubation occurred in 37/338 subjects (11%). Females (13%, 31/232) responded more often than males (6%, 6/106). In logistic regression, the risk of responsiveness was increased with female sex (odds ratio [ORadjusted]=2.7; 95% confidence interval [CI], 1.1-7.6; P=0.022) and was decreased with continuous anaesthesia before laryngoscopy (ORadjusted=0.43; 95% CI, 0.20-0.96; P=0.041). Responses were more likely to occur after a command to respond (and not to nonsense, 13 subjects) than after a nonsense statement (and not to command, four subjects, P=0.049). CONCLUSIONS: Connected consciousness occured after intubation in 11% of young adults, with females at increased risk. Continuous exposure to anaesthesia between induction of anaesthesia and tracheal intubation should be considered to reduce the incidence of connected consciousness. Further research is required to understand sex-related differences in the risk of connected consciousness.

Performance of the SEDLine Monitor: Age Dependency and Time Delay.

BACKGROUND: Devices monitoring the hypnotic component of general anesthesia can help to guide anesthetic management. The main purposes of these devices are the titration of anesthesia dose. While anesthesia at low doses can result in awareness with intraoperative memory formation, excessive administration of anesthetics may be associated with an increased risk of postoperative neurocognitive disorder. We have previously shown for various indices that they are significantly influenced by the patient's age and that the monitors have a significant time delay. Here, we evaluated the influence of patient's age and time delay on the patient state index (PSI) of the SEDLine monitor. METHODS: To analyze the influence of the patient's age, we replayed 2 minutes of electroencephalography (EEG) of 141 patients (19-88 years, ASA I-IV) undergoing general anesthesia maintained with desflurane, sevoflurane, or propofol to the SEDLine monitor. We extracted the PSI as well as the spectral edge frequency (SEF) and performed a linear regression analysis. For evaluation of the time delay, we replayed 5 minutes of EEG of stable episodes of adequate anesthesia (PSI between 25 and 50) or light sedation/wake (PSI >70) in different orders to the SEDLine to simulate sudden changes between the states. Time delays were defined as the required time span of the monitor to reach the stable target index. RESULTS: PSI and SEF increased significantly with the patient's age. These findings did not depend on the administered anesthetic. The evaluation of the correlation between SEF and PSI showed a strong correlation with Spearman's correlation coefficient of ρ = 0.86 (0.82; 0.89). The time delays depended on the type of transition. We found a median time delay of 54 (Min: 46; Max: 61) seconds for the important transition between adequate anesthesia and awake and 55 (Min: 50; Max: 67) seconds in the other direction. CONCLUSIONS: With our analyses, we show that the indices presented on the SEDLine display, the PSI and the SEF, increase with age for patients under general anesthesia. Additionally, a delay of the PSI to react to sudden neurophysiologic changes due to dose of the maintenance anesthetic is of a time course that is clinically significant. These factors should be considered when navigating anesthesia relying on only the proprietary index for the SEDLine monitor.

The First Derivative of the Electroencephalogram Facilitates Tracking of Electroencephalographic Alpha Band Activity During General Anesthesia.

BACKGROUND: Intraoperative neuromonitoring can help to navigate anesthesia. Pronounced alpha oscillations in the frontal electroencephalogram (EEG) appear to predict favorable perioperative neurocognitive outcomes and may also provide a measure of intraoperative antinociception. Monitoring the presence and strength of these alpha oscillations can be challenging, especially in elderly patients, because the EEG in these patients may be dominated by oscillations in other frequencies. Hence, the information regarding alpha oscillatory activity may be hidden and hard to visualize on a screen. Therefore, we developed an effective approach to improve the detection and presentation of alpha activity in the perioperative setting. METHODS: We analyzed EEG records of 180 patients with a median age of 60 years (range, 18-90 years) undergoing noncardiac, nonneurologic surgery under general anesthesia with propofol induction and sevoflurane maintenance. We calculated the power spectral density (PSD) for the unprocessed EEG as well as for the time-discrete first derivative of the EEG (diffPSD) from 10-second epochs. Based on these data, we estimated the power-law coefficient κ of the PSD and diffPSD, as the EEG coarsely follows a 1/fκ distribution when displayed in double logarithmic coordinates. In addition, we calculated the alpha (7.8-12.1 Hz) to delta (0.4-4.3 Hz) ratio from the PSD as well as diffPSD. RESULTS: The median κ was 0.899 [first and third quartile: 0.786, 0.986] for the unaltered PSD, and κ = -0.092 [-0.202, -0.013] for the diffPSD, corresponding to an almost horizontal PSD of the differentiated EEG. The alpha-to-delta ratio of the diffPSD was strongly increased (median ratio = -8.0 dB [-10.5, -4.7 dB] for the unaltered PSD versus 30.1 dB [26.1, 33.8 dB] for the diffPSD). A strong narrowband oscillatory alpha power component (>20% of total alpha power) was detected in 23% using PSD, but in 96% of the diffPSD. CONCLUSIONS: We demonstrated that the calculation of the diffPSD from the time-discrete derivative of the intraoperative frontal EEG is a straightforward approach to improve the detection of alpha activity by eliminating the broadband background noise. This improvement in alpha peak detection and visualization could facilitate the guidance of general anesthesia and improve patient outcome.

Electrical stimulation of the ventral tegmental area restores consciousness from sevoflurane-, dexmedetomidine-, and fentanyl-induced unconsciousness in rats.

BACKGROUND: Dopaminergic neurons in the ventral tegmental area (VTA) are crucially involved in regulating arousal, making them a potential target for reversing general anesthesia. Electrical deep brain stimulation (DBS) of the VTA restores consciousness in animals anesthetized with drugs that primarily enhance GABAA receptors. However, it is unknown if VTA DBS restores consciousness in animals anesthetized with drugs that target other receptors. OBJECTIVE: To evaluate the efficacy of VTA DBS in restoring consciousness after exposure to four anesthetics with distinct receptor targets. METHODS: Sixteen adult Sprague-Dawley rats (8 female, 8 male) with bipolar electrodes implanted in the VTA were exposed to dexmedetomidine, fentanyl, ketamine, or sevoflurane to produce loss of righting, a proxy for unconsciousness. After receiving the dopamine D1 receptor antagonist, SCH-23390, or saline (vehicle), DBS was initiated at 30 µA and increased by 10 µA until reaching a maximum of 100 µA. The current that evoked behavioral arousal and restored righting was recorded for each anesthetic and compared across drug (saline/SCH-23390) condition. Electroencephalogram, heart rate and pulse oximetry were recorded continuously. RESULTS: VTA DBS restored righting after sevoflurane, dexmedetomidine, and fentanyl-induced unconsciousness, but not ketamine-induced unconsciousness. D1 receptor antagonism diminished the efficacy of VTA stimulation following sevoflurane and fentanyl, but not dexmedetomidine. CONCLUSIONS: Electrical DBS of the VTA restores consciousness in animals anesthetized with mechanistically distinct drugs, excluding ketamine. The involvement of the D1 receptor in mediating this effect is anesthetic-specific.

Preoperative Midazolam and Patient-Centered Outcomes of Older Patients: The I-PROMOTE Randomized Clinical Trial.

Importance: The effect of oral midazolam premedication on patient satisfaction in older patients undergoing surgery is unclear, despite its widespread use. Objective: To determine the differences in global perioperative satisfaction in patients with preoperative administration of oral midazolam compared with placebo. Design, Setting, and Participants: This double-blind, parallel-group, placebo-controlled randomized clinical trial was conducted in 9 German hospitals between October 2017 and May 2019 (last follow-up, June 24, 2019). Eligible patients aged 65 to 80 years who were scheduled for elective inpatient surgery for at least 30 minutes under general anesthesia and with planned extubation were enrolled. Data were analyzed from November 2019 to December 2020. Interventions: Patients were randomized to receive oral midazolam, 3.75 mg (n = 309), or placebo (n = 307) 30 to 45 minutes prior to anesthesia induction. Main Outcomes and Measures: The primary outcome was global patient satisfaction evaluated using the self-reported Evaluation du Vécu de l'Anesthésie Generale (EVAN-G) questionnaire on the first postoperative day. Key secondary outcomes included sensitivity and subgroup analyses of the primary outcome, perioperative patient vital data, adverse events, serious complications, and cognitive and functional recovery up to 30 days postoperatively. Results: Among 616 randomized patients, 607 were included in the primary analysis. Of these, 377 (62.1%) were male, and the mean (SD) age was 71.9 (4.4) years. The mean (SD) global index of patient satisfaction did not differ between the midazolam and placebo groups (69.5 [10.7] vs 69.6 [10.8], respectively; mean difference, -0.2; 95% CI, -1.9 to 1.6; P = .85). Sensitivity (per-protocol population, multiple imputation) and subgroup analyses (anxiety, frailty, sex, and previous surgical experience) did not alter the primary results. Secondary outcomes did not differ, except for a higher proportion of patients with hypertension (systolic blood pressure ≥160 mm Hg) at anesthesia induction in the placebo group. Conclusion and Relevance: A single low dose of oral midazolam premedication did not alter the global perioperative patient satisfaction of older patients undergoing surgery or that of patients with anxiety. These results may be affected by the low dose of oral midazolam. Further trials-including a wider population with commonplace low-dose intravenous midazolam and plasma level measurements-are needed. Trial Registration: ClinicalTrials.gov Identifier: NCT03052660.

Permutation entropy is not an age-independent parameter for EEG-based anesthesia monitoring.

Background: An optimized anesthesia monitoring using electroencephalographic (EEG) information in the elderly could help to reduce the incidence of postoperative complications. Processed EEG information that is available to the anesthesiologist is affected by the age-induced changes of the raw EEG. While most of these methods indicate a "more awake" patient with age, the permutation entropy (PeEn) has been proposed as an age-independent measure. In this article, we show that PeEn is also influenced by age, independent of parameter settings. Methods: We retrospectively analyzed the EEG of more than 300 patients, recorded during steady state anesthesia without stimulation, and calculated the PeEn for different embedding dimensions m that was applied to the EEG filtered to a wide variety of frequency ranges. We constructed linear models to evaluate the relationship between age and PeEn. To compare our results to published studies, we also performed a stepwise dichotomization and used non-parametric tests and effect sizes for pairwise comparisons. Results: We found a significant influence of age on PeEn for all settings except for narrow band EEG activity. The analysis of the dichotomized data also revealed significant differences between old and young patients for the PeEn settings used in published studies. Conclusion: Based on our findings, we could show the influence of age on PeEn. This result was independent of parameter, sample rate, and filter settings. Hence, age should be taken into consideration when using PeEn to monitor patient EEG.

The influence of age on EEG-based anaesthesia indices.

STUDY OBJECTIVE: In the upcoming years there will be a growing number of elderly patients requiring general anaesthesia. As age is an independent risk factor for postoperative delirium (POD) the incidence of POD will increase concordantly. One approach to reduce the risk of POD would be to avoid excessively high doses of anaesthetics by using neuromonitoring to guide anaesthesia titration. Therefore, we evaluated the influence of patient's age on various electroencephalogram (EEG)-based anaesthesia indices. DESIGN AND PATIENTS: We conducted an analysis of previously published data by replaying single electrode EEG episodes of maintenance of general anaesthesia from 180 patients (18-90 years; ASA I-IV) into the five different commercially available monitoring systems and evaluated their indices. We included the State/Response Entropy, Narcotrend, qCON/qNOX, bispectral index (BIS), and Treaton MGA-06. For a non-commercial comparison, we extracted the spectral edge frequency (SEF) from the BIS. To evaluate the influence of the age we generated linear regression models. We also assessed the correlation between the various indices. MAIN RESULTS: During anaesthetic maintenance the values of the SEF, State/Response Entropy, qCON/qNOX and BIS all significantly increased (0.05 Hz/0.19-0.26 index points per year) with the patient's age (p < 0.001); whereas the Narcotrend did not change significantly with age (0.06 index points per year; p = 0.28). The index values of the Treaton device significantly decreased with age (-0.09 index points per year; p < 0.001). These findings were independent of the administered dose of anaesthetics. CONCLUSIONS: Almost all current neuromonitoring devices are influenced by age, with the potential to result in inappropriately high dosage of anaesthetics. Therefore, anaesthesiologists should be aware of this phenomenon, and the next generation of monitors should correct for these changes.

Age-Related EEG Features of Bursting Activity During Anesthetic-Induced Burst Suppression.

Electroencephalographic (EEG) Burst Suppression (BSUPP) is a discontinuous pattern characterized by episodes of low voltage disrupted by bursts of cortical synaptic activity. It can occur while delivering high-dose anesthesia. Current research suggests an association between BSUPP and the occurrence of postoperative delirium in the post-anesthesia care unit (PACU) and beyond. We investigated burst micro-architecture to further understand how age influences the neurophysiology of this pharmacologically-induced state. We analyzed a subset of EEG recordings (n = 102) taken from a larger data set previously published. We selected the initial burst that followed a visually identified "silent second," i.e., at least 1 s of iso-electricity of the EEG during propofol induction. We derived the (normalized) power spectral density [(n)PSD], the alpha band power, the maximum amplitude, the maximum slope of the EEG as well as the permutation entropy (PeEn) for the first 1.5 s of the initial burst of each patient. In the old patients >65 years, we observed significantly lower (p < 0.001) EEG power in the 1-15 Hz range. In general, their EEG contained a significantly higher amount of faster oscillations (>15 Hz). Alpha band power (p < 0.001), EEG amplitude (p = 0.001), and maximum EEG slope (p = 0.045) all significantly decreased with age, whereas PeEn increased (p = 0.008). Hence, we can describe an age-related change in features during EEG burst suppression. Sub-group analysis revealed no change in results based on pre-medication. These EEG changes add knowledge to the impact of age on cortical synaptic activity. In addition to a reduction in EEG amplitude, age-associated burst features can complicate the identification of excessive anesthetic administration in patients under general anesthesia. Knowledge of these neurophysiologic changes may not only improve anesthesia care through improved detection of burst suppression but might also provide insight into changes in neuronal network organization in patients at risk for age-related neurocognitive problems.