A Critical Review of Mindfulness Measures.

Background and Purpose: Mindfulness has been associated with many positive psychological benefits. It is usually measured by self-report, and there are numerous questionnaires available to measure mindfulness in this way. The purpose of this review is to offer a summary of the available self-assessment questionnaires for measuring mindfulness, their appropriate uses, and psychometrics. Methods: CINAHL, PubMed, and PsychINFO databases were queried along with hand searching reference lists based on the indicated criteria, including Mindfulness-Based Stress Reduction-related mindfulness measurement tools, based on self-report and designed for use in adults. Results: Fourteen tools, published between 2001 and 2021, were included in this review. The tools varied in their orientation and have been created to measure mindfulness as a state, trait, and process. Conclusions: There is a wide variety of available tools, and each conceptualizes mindfulness in a distinct way. Understanding these details is crucial to choosing the proper tool.

Exploring the postoperative pain experiences of individuals with opioid use disorder and the nurses providing care in the USA: A qualitative descriptive study protocol.

INTRODUCTION: The goal of this study is to gain firsthand insights from individuals with a history of opioid use disorder (OUD) using medication for OUD on their experiences with postoperative pain care. This study also seeks to describe the experiences of nurses caring for individuals with OUD, and the challenges they may face managing complaints of pain in this population. Research suggests that hospitals can significantly enhance the quality of the care they deliver by investigating an individual's experience in the care setting. These insights will allow for the development of strategies for nurses to deepen their understanding of and, therefore, advocate and improve care for, this vulnerable and often stigmatised population. METHODS AND ANALYSIS: A qualitative descriptive study will be conducted consisting of a prescreening and demographics questionnaire, and individual semistructured interviews with approximately 10-15 individuals with OUD having recently undergone surgery and 10-15 nurses providing care for this population for a total of 20-30 interviews. This approach involves the collection of separate but complementary data (ie, perceptions of individuals with OUD and nurses) concerning the phenomena of postoperative pain management. Sampling will continue until data saturation is reached. Descriptive statistics and thematic analysis will then be used. Reporting will adhere to the Standards for Reporting Qualitative Research checklist. ETHICS AND DISSEMINATION: This study received approval from the Institutional Review Board at Northeastern University. Alongside peer-reviewed journal publications, the findings will be presented at relevant conferences, and a plain language summary will be distributed to the study participants.

Evaluating Pain, Opioids, and Delirium in Critically Ill Older Adults.

Untreated pain and pain management with opioids are independent precipitating factors for delirium. This retrospective study evaluated the relationships among pain severity, its management with opioids, and the onset of delirium in older adult patients admitted to the surgical intensive care unit (SICU). Consecutive patients aged 65 or greater admitted to the SICU over a 5-month period were examined (n = 172). When assessed using a multivariable general estimating equation model, opioids (chi-square [χ2], 12.34, p = .0004), but not pain (χ2, 3.31, p = .0688) were significant in predicting next-day delirium status. Controlling for pain, patients exposed to opioids were 2.5 times more likely to develop delirium than patients not exposed (95% Confidence Interval: 1.44-4.36). Our data shows that opioid administration predicted the onset of next-day delirium. In an effort to prevent delirium, future research should focus on opioid-sparing pain management approaches to mitigate pain and delirium.

Evaluating delirium outcomes among older adults in the surgical intensive care unit.

BACKGROUND: Delirium is prevalent in hospitalized older adults. Little is known about delirium among older adults admitted to the surgical intensive care unit (SICU). OBJECTIVES: The purpose of this study was to describe the incidence of delirium, length of stay, 30-day readmission and mortality rates experienced by older adults in the SICU before and after a nurse-driven protocol for delirium-informed care. METHODS: This study employed a retrospective observational cohort design. Consecutive patients 65 years or older admitted to the SICU over six-month periods were compared before (n = 101) and following (n = 172) a nurse-driven protocol for delirium-informed care. Patient-level outcomes included incidence delirium, SICU and hospital length of stay, 30-day readmission and mortality rates. All measures were collected using medical record review. RESULTS: In the pre- and post-intervention cohorts, 37% (37/101) and 33% (56/172) of patients screened positive for delirium, respectively. Following implementation of the delirium-informed care intervention, the number of days where no CAM-ICU assessment was performed significantly decreased (Pre 1.1 ± 1.4; Post 0.45 ± 0.65; p <0.001) and the number of negative assessments significantly increased (Pre 2.45 ± 1.66; Post 2.94 ± 1.69; p < 0.0178), indicating that nurses post-intervention were more consistently assessing for delirium. CONCLUSIONS: This study failed to show improvements in patient outcomes (SICU and hospital length of stay, 30-day readmission and mortality rates), before and following a delirium-informed care intervention. However, positive trends in the data suggest that delirium-informed care has the potential to increase rates of assessment and delirium identification, thereby providing the foundation for reducing the consequences of delirium and improve patient-level outcomes. Further better controlled prospective work is needed to validate this intervention.

Repeat-dose ketamine augmentation for treatment-resistant depression with chronic suicidal ideation: A randomized, double blind, placebo controlled trial.

BACKGROUND: Several studies indicate that ketamine has rapid antidepressant effects in patients with treatment-resistant depression (TRD). The extent to which repeated doses of ketamine (versus placebo) reduce depression in the short and long term among outpatients with TRD and chronic, current suicidal ideation remains unknown. METHODS: Twenty-six medicated outpatients with severe major depressive disorder with current, chronic suicidal ideation were randomized in a double-blind fashion to six ketamine infusions (0.5 mg/kg over 45 minutes) or saline placebo over three weeks. Depression and suicidal ideation were assessed at baseline, 240 min post-infusion, and during a three-month follow-up phase. RESULTS: During the infusion phase, there was no differences in depression severity or suicidal ideation between placebo and ketamine (p = 0.47 and p = 0.32, respectively). At the end of the infusion phase, two patients in the ketamine group and one in the placebo group met criteria for remission of depression. At three-month follow-up, two patients in each group met criteria for remission from depression. LIMITATIONS: Limitations include the small sample size, uncontrolled outpatient medication regimens, and restriction to outpatients, which may have resulted in lower levels of suicidal ideation than would be seen in emergency or inpatient settings. CONCLUSIONS: Repeated, non-escalating doses of ketamine did not outperform placebo in this double-blind, placebo controlled study of patients with severe TRD and current, chronic suicidal ideation. This result may support our previously published open-label data that, in this severely and chronically ill outpatient population, the commonly used dose of 0.5 mg/kg is not sufficient.

Evaluating the use of dexmedetomidine for the reduction of delirium: An integrative review.

Delirium, an acute change in cognition and attention not secondary to a pre-existing condition or dementia, affects nearly 40,000 hospitalized older adults in the United States every day. Delirium is associated with increased healthcare costs of $16,303 to $64,421 per patient. To date, no single pharmacological intervention is effective in preventing or treating delirium in critically ill patients. Evidence suggests the alpha-2 agonist, dexmedetomidine, may reduce or prevent delirium. An integrative review examined whether dexmedetomidine was associated with a lower incidence of delirium compared to other analgesic and sedation strategies. PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guided this review and 16 publications met quality criteria for inclusion. These studies support that postoperative administration of dexmedetomidine may reduce delirium in patients, particularly following cardiac surgery. Further research is needed to determine the benefits of dexmedetomidine in patients on mechanical ventilation and optimal timing and duration of administration.

Multimodal General Anesthesia: Theory and Practice.

Balanced general anesthesia, the most common management strategy used in anesthesia care, entails the administration of different drugs together to create the anesthetic state. Anesthesiologists developed this approach to avoid sole reliance on ether for general anesthesia maintenance. Balanced general anesthesia uses less of each drug than if the drug were administered alone, thereby increasing the likelihood of its desired effects and reducing the likelihood of its side effects. To manage nociception intraoperatively and pain postoperatively, the current practice of balanced general anesthesia relies almost exclusively on opioids. While opioids are the most effective antinociceptive agents, they have undesirable side effects. Moreover, overreliance on opioids has contributed to the opioid epidemic in the United States. Spurred by concern of opioid overuse, balanced general anesthesia strategies are now using more agents to create the anesthetic state. Under these approaches, called "multimodal general anesthesia," the additional drugs may include agents with specific central nervous system targets such as dexmedetomidine and ones with less specific targets, such as magnesium. It is postulated that use of more agents at smaller doses further maximizes desired effects while minimizing side effects. Although this approach appears to maximize the benefit-to-side effect ratio, no rational strategy has been provided for choosing the drug combinations. Nociception induced by surgery is the primary reason for placing a patient in a state of general anesthesia. Hence, any rational strategy should focus on nociception control intraoperatively and pain control postoperatively. In this Special Article, we review the anatomy and physiology of the nociceptive and arousal circuits, and the mechanisms through which commonly used anesthetics and anesthetic adjuncts act in these systems. We propose a rational strategy for multimodal general anesthesia predicated on choosing a combination of agents that act at different targets in the nociceptive system to control nociception intraoperatively and pain postoperatively. Because these agents also decrease arousal, the doses of hypnotics and/or inhaled ethers needed to control unconsciousness are reduced. Effective use of this strategy requires simultaneous monitoring of antinociception and level of unconsciousness. We illustrate the application of this strategy by summarizing anesthetic management for 4 representative surgeries.

Minimizing ICU Neurological Dysfunction with Dexmedetomidine-induced Sleep (MINDDS): protocol for a randomised, double-blind, parallel-arm, placebo-controlled trial.

INTRODUCTION: Delirium, which is prevalent in postcardiac surgical patients, is an acute brain dysfunction characterised by disturbances in attention, awareness and cognition not explained by a pre-existing neurocognitive disorder. The pathophysiology of delirium remains poorly understood. However, basic science and clinical studies suggest that sleep disturbance may be a modifiable risk factor for the development of delirium. Dexmedetomidine is a α-2A adrenergic receptor agonist medication that patterns the activity of various arousal nuclei similar to sleep. A single night-time loading dose of dexmedetomidine promotes non-rapid eye movement sleep stages N2 and N3 sleep. This trial hypothesises dexmedetomidine-induced sleep as pre-emptive therapy for postoperative delirium. METHODS AND ANALYSIS: The MINDDS (Minimizing ICU Neurological Dysfunction with Dexmedetomidine-induced Sleep) trial is a 370-patient block-randomised, placebo-controlled, double-blinded, single-site, parallel-arm superiority trial. Patients over 60 years old, undergoing cardiac surgery with planned cardiopulmonary bypass, will be randomised to receive a sleep-inducing dose of dexmedetomidine or placebo. The primary outcome is the incidence of delirium on postoperative day 1, assessed with the Confusion Assessment Method by staff blinded to the treatment assignment. To ensure that the study is appropriately powered for the primary outcome measure, patients will be recruited and randomised into the study until 370 patients receive the study intervention on postoperative day 0. Secondary outcomes will be evaluated by in-person assessments and medical record review for in-hospital end points, and by telephone interview for 30-day, 90-day and 180-day end points. All trial outcomes will be evaluated using an intention-to-treat analysis plan. Hypothesis testing will be performed using a two-sided significance level (type I error) of α=0.05. Sensitivity analyses using the actual treatment received will be performed and compared with the intention-to-treat analysis results. Additional sensitivity analyses will assess the potential impact of missing data due to loss of follow-up. ETHICS AND DISSEMINATION: The Partners Human Research Committee approved the MINDDS trial. Recruitment began in March 2017. Dissemination plans include presentations at scientific conferences, scientific publications and popular media. TRIAL REGISTRATION NUMBER: NCT02856594.

Dexmedetomidine promotes biomimetic non-rapid eye movement stage 3 sleep in humans: A pilot study.

OBJECTIVES: Sleep, which comprises of rapid eye movement (REM) and non-REM stages 1-3 (N1-N3), is a natural occurring state of decreased arousal that is crucial for normal cardiovascular, immune and cognitive function. The principal sedative drugs produce electroencephalogram beta oscillations, which have been associated with neurocognitive dysfunction. Pharmacological induction of altered arousal states that neurophysiologically approximate natural sleep, termed biomimetic sleep, may eliminate drug-induced neurocognitive dysfunction. METHODS: We performed a prospective, single-site, three-arm, randomized-controlled, crossover polysomnography pilot study (n = 10) comparing natural, intravenous dexmedetomidine- (1-µg/kg over 10 min [n = 7] or 0.5-µg/kg over 10 min [n = 3]), and zolpidem-induced sleep in healthy volunteers. Sleep quality and psychomotor performance were assessed with polysomnography and the psychomotor vigilance test, respectively. Sleep quality questionnaires were also administered. RESULTS: We found that dexmedetomidine promoted N3 sleep in a dose dependent manner, and did not impair performance on the psychomotor vigilance test. In contrast, zolpidem extended release was associated with decreased theta (∼5-8 Hz; N2 and N3) and increased beta oscillations (∼13-25 Hz; N2 and REM). Zolpidem extended release was also associated with increased lapses on the psychomotor vigilance test. No serious adverse events occurred. CONCLUSIONS: Pharmacological induction of biomimetic N3 sleep with psychomotor sparing benefits is feasible. SIGNIFICANCE: These results suggest that α2a adrenergic agonists may be developed as a new class of sleep enhancing medications with neurocognitive sparing benefits.

Lack of Responsiveness during the Onset and Offset of Sevoflurane Anesthesia Is Associated with Decreased Awake-Alpha Oscillation Power.

Anesthetic drugs are typically administered to induce altered states of arousal that range from sedation to general anesthesia (GA). Systems neuroscience studies are currently being used to investigate the neural circuit mechanisms of anesthesia-induced altered arousal states. These studies suggest that by disrupting the oscillatory dynamics that are associated with arousal states, anesthesia-induced oscillations are a putative mechanism through which anesthetic drugs produce altered states of arousal. However, an empirical clinical observation is that even at relatively stable anesthetic doses, patients are sometimes intermittently responsive to verbal commands during states of light sedation. During these periods, prominent anesthesia-induced neural oscillations such as slow-delta (0.1-4 Hz) oscillations are notably absent. Neural correlates of intermittent responsiveness during light sedation have been insufficiently investigated. A principled understanding of the neural correlates of intermittent responsiveness may fundamentally advance our understanding of neural dynamics that are essential for maintaining arousal states, and how they are disrupted by anesthetics. Therefore, we performed a high-density (128 channels) electroencephalogram (EEG) study (n = 8) of sevoflurane-induced altered arousal in healthy volunteers. We administered temporally precise behavioral stimuli every 5 s to assess responsiveness. Here, we show that decreased eyes-closed, awake-alpha (8-12 Hz) oscillation power is associated with lack of responsiveness during sevoflurane effect-onset and -offset. We also show that anteriorization-the transition from occipitally dominant awake-alpha oscillations to frontally dominant anesthesia induced-alpha oscillations-is not a binary phenomenon. Rather, we suggest that periods, which were defined by lack of responsiveness, represent an intermediate brain state. We conclude that awake-alpha oscillation, previously thought to be an idling rhythm, is associated with responsiveness to behavioral stimuli.

A Prospective Study of Age-dependent Changes in Propofol-induced Electroencephalogram Oscillations in Children.

BACKGROUND: In adults, frontal electroencephalogram patterns observed during propofol-induced unconsciousness consist of slow oscillations (0.1 to 1 Hz) and coherent alpha oscillations (8 to 13 Hz). Given that the nervous system undergoes significant changes during development, anesthesia-induced electroencephalogram oscillations in children may differ from those observed in adults. Therefore, we investigated age-related changes in frontal electroencephalogram power spectra and coherence during propofol-induced unconsciousness. METHODS: We analyzed electroencephalogram data recorded during propofol-induced unconsciousness in patients between 0 and 21 yr of age (n = 97), using multitaper spectral and coherence methods. We characterized power and coherence as a function of age using multiple linear regression analysis and within four age groups: 4 months to 1 yr old (n = 4), greater than 1 to 7 yr old (n = 16), greater than 7 to 14 yr old (n = 30), and greater than 14 to 21 yr old (n = 47). RESULTS: Total electroencephalogram power (0.1 to 40 Hz) peaked at approximately 8 yr old and subsequently declined with increasing age. For patients greater than 1 yr old, the propofol-induced electroencephalogram structure was qualitatively similar regardless of age, featuring slow and coherent alpha oscillations. For patients under 1 yr of age, frontal alpha oscillations were not coherent. CONCLUSIONS: Neurodevelopmental processes that occur throughout childhood, including thalamocortical development, may underlie age-dependent changes in electroencephalogram power and coherence during anesthesia. These age-dependent anesthesia-induced electroencephalogram oscillations suggest a more principled approach to monitoring brain states in pediatric patients.

Ketamine augmentation for outpatients with treatment-resistant depression: Preliminary evidence for two-step intravenous dose escalation.

OBJECTIVE: Preliminary evidence supports the safety and efficacy of subanesthetic ketamine as an experimental antidepressant, although its effects are often not sustained beyond one week. Studies are lacking that have examined the sustained effects of escalating ketamine doses as augmentation in outpatients with treatment-resistant depression. Therefore, the aims of this study were twofold: (1) to assess the safety and antidepressant efficacy of two-step, repeated-dose ketamine augmentation and (2) to assess the duration of ketamine's antidepressant efficacy as augmentation to ongoing antidepressant pharmacotherapy for 3 months after the final infusion. METHODS: Fourteen patients with treatment-resistant depression were eligible to receive augmentation with six open-label intravenous ketamine infusions over 3 weeks. For the first three infusions, ketamine was administered at a dose of 0.5 mg/kg over 45 minutes; the dose was increased to 0.75 mg/kg over 45 minutes for the subsequent three infusions. The primary outcome measure was response (as measured on Hamilton Depression Rating Scale-28 items). RESULTS: After the completion of three ketamine infusions, 7.1% (1/14) responded; after all six ketamine infusions, 41.7% (5/12) completers responded and 16.7% (2/12) remitted. Intent-to-treat response and remission rates at the end of the final infusion were 35.7% (5/14) and 14.3% (2/14), respectively. However, all but one responder relapsed within 2 weeks after the final infusion. CONCLUSION: Repeated, escalating doses of intravenous ketamine augmentation were preliminarily found to be feasible, efficacious and well tolerated. Interaction with concomitant medications and elevated level of treatment resistance are possible factors for non-response.

Spatiotemporal Dynamics of Dexmedetomidine-Induced Electroencephalogram Oscillations.

An improved understanding of the neural correlates of altered arousal states is fundamental for precise brain state targeting in clinical settings. More specifically, electroencephalogram recordings are now increasingly being used to relate drug-specific oscillatory dynamics to clinically desired altered arousal states. Dexmedetomidine is an anesthetic adjunct typically administered in operating rooms and intensive care units to produce and maintain a sedative brain state. However, a high-density electroencephalogram characterization of the neural correlates of the dexmedetomidine-induced altered arousal state has not been previously accomplished. Therefore, we administered dexmedetomidine (1mcg/kg bolus over 10 minutes, followed by 0.7mcg/kg/hr over 50 minutes) and recorded high-density electroencephalogram signals in healthy volunteers, 18-36 years old (n = 8). We analyzed the data with multitaper spectral and global coherence methods. We found that dexmedetomidine was associated with increased slow-delta oscillations across the entire scalp, increased theta oscillations in occipital regions, increased spindle oscillations in frontal regions, and decreased beta oscillations across the entire scalp. The theta and spindle oscillations were globally coherent. During recovery from this state, these electroencephalogram signatures reverted towards baseline signatures. We report that dexmedetomidine-induced electroencephalogram signatures more closely approximate the human sleep onset process than previously appreciated. We suggest that these signatures may be targeted by real time visualization of the electroencephalogram or spectrogram in clinical settings. Additionally, these signatures may aid the development of control systems for principled neurophysiological based brain-state targeting.

Rapid and Sustained Reductions in Current Suicidal Ideation Following Repeated Doses of Intravenous Ketamine: Secondary Analysis of an Open-Label Study.

BACKGROUND: Ketamine rapidly reduces thoughts of suicide in patients with treatment-resistant depression who are at low risk for suicide. However, the extent to which ketamine reduces thoughts of suicide in depressed patients with current suicidal ideation remains unknown. METHODS: Between April 2012 and October 2013, 14 outpatients with DSM-IV-diagnosed major depressive disorder were recruited for the presence of current, stable (≥ 3 months) suicidal thoughts. They received open-label ketamine infusions over 3 weeks (0.5 mg/kg over 45 minutes for the first 3 infusions; 0.75 mg/kg over 45 minutes for the last 3). In this secondary analysis, the primary outcome measures of suicidal ideation (Columbia-Suicide Severity Rating Scale [C-SSRS] and the Suicide Item of the 28-item Hamilton Depression Rating Scale [HDRS28-SI]) were assessed at 240 minutes postinfusion and for 3 months thereafter in a naturalistic follow-up. RESULTS: Over the course of the infusions (acute treatment phase), 7 of 14 patients (50%) showed remission of suicidal ideation on the C-SSRS Ideation scale (even among patients whose depression did not remit). There was a significant linear decrease in this score over time (P < .001), which approached significance even after controlling for severity of 6-item Hamilton Depression Rating Scale (HDRS6) core depression items (P = .05). Similarly, there were significant decreases in the C-SSRS Intensity (P < .01) and HDRS28-SI (P < .001) scores during the acute treatment phase. Two of the 7 patients who achieved remission during the acute treatment phase (29%) maintained their remission throughout a 3-month naturalistic follow-up. CONCLUSIONS: In this preliminary study, repeated doses of open-label ketamine rapidly and robustly decreased suicidal ideation in pharmacologically treated outpatients with treatment-resistant depression with stable suicidal thoughts; this decrease was maintained for at least 3 months following the final ketamine infusion in 2 patients. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT01582945.

Electroencephalogram signatures of ketamine anesthesia-induced unconsciousness.

OBJECTIVES: Ketamine is an N-methyl-d-aspartate (NMDA) receptor antagonist commonly administered as a general anesthetic. However, neural circuit mechanisms to explain ketamine anesthesia-induced unconsciousness in humans are yet to be clearly defined. Disruption of frontal-parietal network connectivity has been proposed as a mechanism to explain this brain state. However, this mechanism was recently demonstrated at subanesthetic doses of ketamine in awake-patients. Therefore, we investigated whether there is an electroencephalogram (EEG) signature specific for ketamine anesthesia-induced unconsciousness. METHODS: We retrospectively studied the EEG in 12 patients who received ketamine for the induction of general anesthesia. We analyzed the EEG dynamics using power spectral and coherence methods. RESULTS: Following the administration of a bolus dose of ketamine to induce unconsciousness, we observed a "gamma burst" EEG pattern that consisted of alternating slow-delta (0.1-4Hz) and gamma (∼27-40Hz) oscillations. This pattern was also associated with increased theta oscillations (∼4-8Hz) and decreased alpha/beta oscillations (∼10-24Hz). CONCLUSIONS: Ketamine anesthesia-induced unconsciousness is associated with a gamma burst EEG pattern. SIGNIFICANCE: The EEG signature of ketamine anesthesia-induced unconsciousness may offer new insights into NMDA circuit mechanisms for unconsciousness.

GABAA circuit mechanisms are associated with ether anesthesia-induced unconsciousness.

OBJECTIVE: An emerging paradigm for understanding how anesthetics induce altered arousal is relating receptor targeting in specific neural circuits to electroencephalogram (EEG) activity. Enhanced gamma amino-butyric acid A (GABAA) inhibitory post-synaptic currents (IPSCs) manifest with large-amplitude slow (0.1-1Hz) and frontally coherent alpha (8-12Hz) EEG oscillations during general anesthesia. Therefore, we investigated the EEG signatures of modern day derivatives of ether (MDDE) anesthesia to assess the extent to which we could obtain insights into MDDE anesthetic mechanisms. METHODS: We retrospectively studied cases from our database in which patients received isoflurane anesthesia vs. isoflurane/ketamine anesthesia (n=10 each) or desflurane anesthesia vs. desflurane/ketamine anesthesia (n=9 each). We analyzed the EEG recordings with spectral power and coherence methods. RESULTS: Similar to known GABAA circuit level mechanisms, we found that MDDE anesthesia induced large amplitude slow and frontally coherent alpha oscillations. Additionally, MDDE anesthesia also induced frontally coherent theta (4-8Hz) oscillations. Reduction of GABAergic IPSCs with ketamine resulted in beta/gamma (13-40Hz) oscillations, and significantly reduced MDDE anesthesia-induced slow, theta and alpha oscillation power. CONCLUSIONS: Large amplitude slow oscillations and coherent alpha and theta oscillations are moderated by ketamine during MDDE anesthesia. SIGNIFICANCE: These observations are consistent with the notion that GABAA circuit-level mechanisms are associated with MDDE anesthesia-induced unconsciousness.

Nitrous oxide-induced slow and delta oscillations.

OBJECTIVES: Switching from maintenance of general anesthesia with an ether anesthetic to maintenance with high-dose (concentration >50% and total gas flow rate >4 liters per minute) nitrous oxide is a common practice used to facilitate emergence from general anesthesia. The transition from the ether anesthetic to nitrous oxide is associated with a switch in the putative mechanisms and sites of anesthetic action. We investigated whether there is an electroencephalogram (EEG) marker of this transition. METHODS: We retrospectively studied the ether anesthetic to nitrous oxide transition in 19 patients with EEG monitoring receiving general anesthesia using the ether anesthetic sevoflurane combined with oxygen and air. RESULTS: Following the transition to nitrous oxide, the alpha (8-12 Hz) oscillations associated with sevoflurane dissipated within 3-12 min (median 6 min) and were replaced by highly coherent large-amplitude slow-delta (0.1-4 Hz) oscillations that persisted for 2-12 min (median 3 min). CONCLUSIONS: Administration of high-dose nitrous oxide is associated with transient, large amplitude slow-delta oscillations. SIGNIFICANCE: We postulate that these slow-delta oscillations may result from nitrous oxide-induced blockade of major excitatory inputs (NMDA glutamate projections) from the brainstem (parabrachial nucleus and medial pontine reticular formation) to the thalamus and cortex. This EEG signature of high-dose nitrous oxide may offer new insights into brain states during general anesthesia.

Clinical Electroencephalography for Anesthesiologists: Part I: Background and Basic Signatures.

The widely used electroencephalogram-based indices for depth-of-anesthesia monitoring assume that the same index value defines the same level of unconsciousness for all anesthetics. In contrast, we show that different anesthetics act at different molecular targets and neural circuits to produce distinct brain states that are readily visible in the electroencephalogram. We present a two-part review to educate anesthesiologists on use of the unprocessed electroencephalogram and its spectrogram to track the brain states of patients receiving anesthesia care. Here in part I, we review the biophysics of the electroencephalogram and the neurophysiology of the electroencephalogram signatures of three intravenous anesthetics: propofol, dexmedetomidine, and ketamine, and four inhaled anesthetics: sevoflurane, isoflurane, desflurane, and nitrous oxide. Later in part II, we discuss patient management using these electroencephalogram signatures. Use of these electroencephalogram signatures suggests a neurophysiologically based paradigm for brain state monitoring of patients receiving anesthesia care.

Disruption of thalamic functional connectivity is a neural correlate of dexmedetomidine-induced unconsciousness.

Understanding the neural basis of consciousness is fundamental to neuroscience research. Disruptions in cortico-cortical connectivity have been suggested as a primary mechanism of unconsciousness. By using a novel combination of positron emission tomography and functional magnetic resonance imaging, we studied anesthesia-induced unconsciousness and recovery using the α2-agonist dexmedetomidine. During unconsciousness, cerebral metabolic rate of glucose and cerebral blood flow were preferentially decreased in the thalamus, the Default Mode Network (DMN), and the bilateral Frontoparietal Networks (FPNs). Cortico-cortical functional connectivity within the DMN and FPNs was preserved. However, DMN thalamo-cortical functional connectivity was disrupted. Recovery from this state was associated with sustained reduction in cerebral blood flow and restored DMN thalamo-cortical functional connectivity. We report that loss of thalamo-cortical functional connectivity is sufficient to produce unconsciousness.

Effects of sevoflurane and propofol on frontal electroencephalogram power and coherence.

BACKGROUND: The neural mechanisms of anesthetic vapors have not been studied in depth. However, modeling and experimental studies on the intravenous anesthetic propofol indicate that potentiation of γ-aminobutyric acid receptors leads to a state of thalamocortical synchrony, observed as coherent frontal alpha oscillations, associated with unconsciousness. Sevoflurane, an ether derivative, also potentiates γ-aminobutyric acid receptors. However, in humans, sevoflurane-induced coherent frontal alpha oscillations have not been well detailed. METHODS: To study the electroencephalogram dynamics induced by sevoflurane, the authors identified age- and sex-matched patients in which sevoflurane (n = 30) or propofol (n = 30) was used as the sole agent for maintenance of general anesthesia during routine surgery. The authors compared the electroencephalogram signatures of sevoflurane with that of propofol using time-varying spectral and coherence methods. RESULTS: Sevoflurane general anesthesia is characterized by alpha oscillations with maximum power and coherence at approximately 10 Hz, (mean ± SD; peak power, 4.3 ± 3.5 dB; peak coherence, 0.73 ± 0.1). These alpha oscillations are similar to those observed during propofol general anesthesia, which also has maximum power and coherence at approximately 10 Hz (peak power, 2.1 ± 4.3 dB; peak coherence, 0.71 ± 0.1). However, sevoflurane also exhibited a distinct theta coherence signature (peak frequency, 4.9 ± 0.6 Hz; peak coherence, 0.58 ± 0.1). Slow oscillations were observed in both cases, with no significant difference in power or coherence. CONCLUSIONS: The study results indicate that sevoflurane, like propofol, induces coherent frontal alpha oscillations and slow oscillations in humans to sustain the anesthesia-induced unconscious state. These results suggest a shared molecular and systems-level mechanism for the unconscious state induced by these drugs.