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Concept: EEG measures during anesthesia

169

General anesthetics are used during medical and surgical procedures to reversibly induce a state of total unconsciousness in patients. Here, we investigate, from a dynamic network perspective, how the cortical and cardiovascular systems behave during anesthesia by applying nonparametric spectral techniques to cortical electroencephalography, electrocardiogram and respiratory signals recorded from anesthetized rats under two drugs, ketamine-xylazine (KX) and pentobarbital (PB). We find that the patterns of low-frequency cortico-cardio-respiratory network interactions may undergo significant changes in network activity strengths and in number of network links at different depths of anesthesia dependent upon anesthetics used.

Concepts: Pharmacology, Surgery, Anesthesia, General anaesthesia, Chloroform, Local anesthetic, Anesthetic, EEG measures during anesthesia

24

Seizure-like behavior is an uncommon yet worrisome phenomenon during anesthesia with propofol. The current case report describes a 23-year-old man admitted for elective surgery who experienced several seizure-like episodes after induction with propofol and during a desflurane-based general anesthetic that were so severe it was not possible to complete the procedure. A second surgery was rescheduled 2 days later with simultaneous scalp electroencephalographic (EEG) recording and general anesthesia with propofol and fentanyl. During the second operation, he again experienced numerous episodes of generalized shaking movements. Simultaneous intraoperative EEG recording showed a background of diffuse beta and alpha frequencies interspersed with periods of pseudoperiodic delta activity; electrographic seizures were not apparent. With this information, muscle relaxants were given and the procedure was performed without difficulty. This is the first report of apparent seizure-like activity during anesthesia with propofol of an otherwise relatively healthy adult, in which concurrent EEG recording demonstrates the nonepileptic nature. The current case demonstrates that, at least in some instances, these concerning movements are not seizure related. Concurrent EEG monitoring may be helpful to evaluate the nature of the episodes in select cases.

Concepts: Surgery, Electroencephalography, Anesthesia, Propofol, Electromyography, Seizure, Delta wave, EEG measures during anesthesia

18

Switching from maintenance of general anesthesia with an ether anesthetic to maintenance with high-dose (concentration >50% and total gas flow rate >4liters 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.

Concepts: Oxygen, Neuroscience, Nitrogen, Electroencephalography, Anesthesia, Delta wave, EEG measures during anesthesia, 1990s American television series

6

Electroencephalogram (EEG) approaches may provide important information about developmental changes in brain-state dynamics during general anesthesia. We used multi-electrode EEG, analyzed with multitaper-spectral methods and video recording of body movement to characterize the spatiotemporal dynamics of brain activity in 36 infants 0-6 months old when awake, and during maintenance-of and emergence-from sevoflurane general anesthesia. During maintenance: 1)slow-delta oscillations were present in all ages; 2)theta and alpha oscillations emerged around 4months; 3)unlike adults, all infants lacked frontal alpha predominance and coherence. Alpha power was greatest during maintenance, compared to awake and emergence in infants at 4-6months. During emergence, theta and alpha power decreased with decreasing sevoflurane concentration in infants at 4-6months. These EEG dynamic differences are likely due to developmental factors including regional differences in synaptogenesis, glucose metabolism, and myelination across the cortex. We demonstrate the need to apply age-adjusted analytic approaches to develop neurophysiologic-based strategies for pediatric anesthetic state monitoring.

Concepts: Brain, Cognitive science, Electroencephalography, Anesthesia, EEG measures during anesthesia

2

Postoperative delirium, arbitrarily defined as occurring within 5 days of surgery, affects up to 50% of patients older than 60 after a major operation. This geriatric syndrome is associated with longer intensive care unit and hospital stay, readmission, persistent cognitive deterioration and mortality. No effective preventive methods have been identified, but preliminary evidence suggests that EEG monitoring during general anaesthesia, by facilitating reduced anaesthetic exposure and EEG suppression, might decrease incident postoperative delirium. This study hypothesises that EEG-guidance of anaesthetic administration prevents postoperative delirium and downstream sequelae, including falls and decreased quality of life.

Concepts: Clinical trial, The Canon of Medicine, Surgery, Avicenna, Anesthesia, General anaesthesia, Local anesthetic, EEG measures during anesthesia

1

The burst-suppression pattern is well recognized as a distinct feature of the mammalian electroencephalogram (EEG) waveform. Consisting of alternating periods of high amplitude oscillatory and isoelectric activity, it can be induced in health by deep anesthesia as well as being evoked by a range of pathophysiological processes that include coma and anoxia. While the electroencephalographic phenomenon and clinical implications of burst suppression have been studied extensively, the physiological mechanisms underlying its emergence remain unresolved and obscure. Because electroencephalographic bursting phenomenologically resembles the bursting observed in single neurons, it would be reasonable to assume that the theoretical insights developed to understand bursting at the cellular (“microscopic”) level would enable insights into the dynamical genesis of bursting at the level of the whole brain (“macroscopic”). In general action potential bursting is the result of the interplay of two time scales: a fast time scale responsible for spiking, and a slow time scale that modulates such activity. We therefore hypothesize that such fast-slow systems dynamically underpin electroencephalographic bursting. Here we show that a well-known mean field dynamical model of the electroencephalogram, the Liley model, while unable to produce burst suppression unmodified, is able to give rise to a wide variety of burst-like activity by the addition of one or more slow systems modulating model parameters speculated to be major “targets” for anesthetic action. The development of a physiologically plausible theoretical framework to account for burst suppression will lead to a more complete physiological understanding of the EEG and the mechanisms that serve to modify ongoing brain activity necessary for purposeful behavior and consciousness.

Concepts: Brain, Action potential, Electrophysiology, Neuroscience, Electroencephalography, Evoked potential, EEG measures during anesthesia

0

Processed electroencephalogram (EEG) monitors help assess the hypnotic state during general anesthesia or sedation. Maintaining the bispectral index (BIS) or state entropy (SE) between 40 and 60 has been recommended to mitigate anesthesia awareness. Nonetheless, SEs > 70 were frequently observed at end-tidal sevoflurane concentrations unlikely to allow awareness. We sought to determine the prevalence of elevated discordant measurements during BIS and SE monitoring.

Concepts: Cognitive science, Anesthesia, Harshad number, General anaesthesia, Amnesia, Hypnotic, Hypnosis, EEG measures during anesthesia

0

Objective. Significant spectral characteristics of electroencephalogram (EEG) patterns exist in individual patients during re-establishing consciousness after general anesthesia. However, these EEG patterns cannot be quantitatively identified using commercially available depth of anesthesia (DoA) monitors. This study proposed an effective classification method and indices to classify these patterns among patients. Approach. Four types of emergence EEG patterns were identified based on EEG data set from 52patients undergoing sevoflurane general anesthesia from two hospitals. Then, the relative power spectrum density (RPSD) of five frequency sub-bands of clinical interest (delta, theta, alpha, beta, and gamma) were selected for emergence state analysis. Finally, the genetic algorithm support vector machine (GA-SVM) was used to identify the emergence EEG patterns. Performance was reported in terms of sensitivity (SE), specificity (SP) and accuracy (AC). Main results. The combination of the mean and mode of RPSD in delta and alpha band (P (delta)/P (alpha) performed the best with the GA-SVM classification. AC indices obtained by GA-SVM across the four patterns were 90.64±7.61, 81.79±5.84, 82.14±7.99, and 72.86±11.11 respectively. Furthermore, the emergence time of the patients with EEG emergence pattern I and III increased with the increasing of patients' age. While for the patients with EEG emergence pattern IV, the emergence time positively correlates with the patients' age which less than 50, and negatively correlates with the patients' age which more than 50. Significance. The mean and mode of P (delta)/P (alpha) is a useful index to classify the different emergence EEG patterns. In addition, the EEG emergence patterns may correlate with underlying neural substrate which related with patients' age.

Concepts: Electroencephalography, Arithmetic mean, Pattern, Skewness, Binary classification, Delta wave, Pattern recognition, EEG measures during anesthesia

0

Although the National Institutes of Health (NIH) invests $30 billion in research annually, many funded studies fail to generate results that can inform practice. The National Institutes of Health introduced a phased funding mechanism as one potential solution. Study-specific milestones are established for an initial pilot phase. We assess the utility of this phased approach through the ongoing Electroencephalography (EEG) Guidance of Anesthesia to Alleviate Geriatric Syndromes (ENGAGES) pragmatic clinical trial. The hypothesis of the trial is that EEG guidance of general anesthesia, through prevention of EEG suppression, can decrease postoperative delirium and its downstream negative sequelae.

Concepts: Health care, Medicine, Clinical trial, The Canon of Medicine, Avicenna, Electroencephalography, Finance, EEG measures during anesthesia

0

Few studies have systematically described relationships between clinical-behavioural signs, electroencephalographic (EEG) patterns and age during emergence from anaesthesia in young children.

Concepts: Observational study, Electroencephalography, Cultural studies, EEG measures during anesthesia