Search

General anesthesia significantly alters brain network connectivity. Graph-theoretical analysis has been used extensively to study static brain networks but may be limited in the study of rapidly changing brain connectivity during induction of or recovery from general anesthesia. Here we introduce a novel method to study the temporal evolution of network modules in the brain. We recorded multichannel electroencephalograms (EEG) from 18 surgical patients who underwent general anesthesia with either propofol (n = 9) or sevoflurane (n = 9). Time series data were used to reconstruct networks; each electroencephalographic channel was defined as a node and correlated activity between the channels was defined as a link. We analyzed the frequency of subgraphs in the network with a defined number of links; subgraphs with a high probability of occurrence were deemed network "backbones." We analyzed the behavior of network backbones across consciousness, anesthetic induction, anesthetic maintenance, and two points of recovery. Constitutive, variable and state-specific backbones were identified across anesthetic state transitions. Brain networks derived from neurophysiologic data can be deconstructed into network backbones that change rapidly across states of consciousness. This technique enabled a granular description of network evolution over time. The concept of network backbones may facilitate graph-theoretical analysis of dynamically changing networks.

In a cerebral hypometabolic state, cortical neurons exhibit slow synchronous oscillatory activity with sparse firing. How such a synchronization spatially organizes as the cerebral metabolic rate decreases have not been systemically investigated. We developed a network model of leaky integrate-and-fire neurons with an additional dependency on ATP dynamics. Neurons were scattered in a 2D space, and their population activity patterns at varying ATP levels were simulated. The model predicted a decrease in firing activity as the ATP production rate was lowered. Under hypometabolic conditions, an oscillatory firing pattern, that is, an ON-OFF cycle arose through a failure of sustainable firing due to reduced excitatory positive feedback and rebound firing after the slow recovery of ATP concentration. The firing rate oscillation of distant neurons developed at first asynchronously that changed into burst suppression and global synchronization as ATP production further decreased. These changes resembled the experimental data obtained from anesthetized rats, as an example of a metabolically suppressed brain. Together, this study substantiates a novel biophysical mechanism of neuronal network synchronization under limited energy supply conditions. [ABSTRACT FROM AUTHOR]

Diversas complicações das vias aéreas podem ocorrer durante a artroscopia do ombro, incluindo obstrução das vias aéreas, punção pleural e enfisema subcutâneo. Levantou‐se a hipótese de que o fluido de irrigação utilizado durante artroscopia do ombro possa aumentar a pressão do balonete do tubo endotraqueal, podendo causar edema e lesão isquêmica na mucosa traqueal. Portanto, este estudo teve como objetivo avaliar a relação entre o fluido de irrigação e a pressão do balonete do tubo endotraqueal. Participaram do estudo 40 pacientes com idades entre 20 e 70 anos com classificação do estado físico I ou II da American Society of Anesthesiologists (ASA), programados para cirurgia artroscópica do ombro, eletiva e sob anestesia geral. Registramos as pressões do balonete do tubo endotraqueal e as circunferências do pescoço a cada hora, a partir do início da cirurgia. Também registramos a duração anestésica e cirúrgica, assim como o volume total de líquido de irrigação empregado. Foi encontrada correlação positiva entre a pressão do balonete do tubo endotraqueal e a quantidade de líquido de irrigação (r = 0,385; 95% IC 0,084 a 0,62; p = 0,0141). A pressão do balonete do tubo endotraqueal registrou aumento significante 2 e 3 horas após o início da cirurgia (p = 0,0368 e p = 0,0245, respectivamente). No entanto, a circunferência do pescoço não mostrou diferença significante. As pressões do balonete do tubo endotraqueal aumentaram com o tempo de cirurgia e com o aumento do volume de líquido de irrigação utilizado em pacientes submetidos a artroscopia do ombro. Recomendamos a monitorização rigorosa da pressão do balonete do tubo endotraqueal durante artroscopia do ombro, especialmente nos procedimentos longos em que grandes volumes de fluido de irrigação são empregados, para evitar complicações causadas por pressões elevadas do balonete. Several airway complications can occur during shoulder arthroscopy including airway obstruction, pleural puncture, and subcutaneous emphysema. It was hypothesized that the irrigation fluid used during a shoulder arthroscopic procedure might increase the cuff pressure of the endotracheal tube, which can cause edema and ischemic damage to the endotracheal mucosa. Therefore, this study aimed to evaluate the relationship between irrigation fluid and endotracheal tube cuff pressures. Forty patients aged 20 to 70 years with an American Society of Anesthesiologists (ASA) score I or II, scheduled for elective arthroscopic shoulder surgery under general anesthesia, participated in our study. We recorded endotracheal tube cuff pressures and neck circumferences every hour from the start of the operation. We also recorded the total duration of the anesthesia, operation, and the total volume of fluid used for irrigation. A positive correlation was shown between endotracheal tube cuff pressures and the amount of irrigation fluid (r = 0.385, 95% CI 0.084 to 0.62, p = 0.0141). The endotracheal tube cuff pressure significantly increased at 2 and 3 hours after starting the operation (p = 0.0368 and p = 0.0245, respectively). However, neck circumference showed no significant difference. Endotracheal tube cuff pressures increased with operation time and with increased volumes of irrigation fluid used in patients who underwent shoulder arthroscopy. We recommend close monitoring of endotracheal tube cuff pressures during shoulder arthroscopy, especially during long operations using a large amount of irrigation fluid, to prevent complications caused by raised cuff pressures. [ABSTRACT FROM AUTHOR]

Introduction Recent evidence suggests that the conscious brain is characterized by a diverse repertoire of functional connectivity patterns while the anesthetized brain shows stereotyped activity. However, classical time-averaged methods of connectivity dismiss dynamic and temporal characteristics of functional configurations. Here we demonstrate a new approach which characterizes time-varying patterns of functional connectivity at the subsecond time scale. Methods We introduce phase-lag entropy (PLE), a measure of the diversity of temporal patterns in the phase relationships between two signals. The proposed measure was applied to multichannel electroencephalogram (EEG), which were recorded from two distinct experimental settings: (1) propofol was administrated at a constant infusion rate for 60 min ( n = 96); (2) administration of propofol by a target effect-site concentration-controlled infusion with simultaneous assessment of the level of consciousness ( n = 10). Results From the first dataset, two substantial changes of the phase relationship during anesthesia was found: (1) the dynamics of the phase relationship between frontal channels became progressively less diverse and more stereotyped during unconsciousness, quantified as a reduction in PLE; and (2) the reduction in PLE was consistent across subjects. Furthermore, PLE provided better performance in the classification of states of consciousness than did phase-lag index, a classical time-averaged connectivity method. From the second dataset, PLE showed the highest agreement with the level of consciousness, compared to existing anesthetic depth indicators. Conclusions This study suggests that a scarcity of functional configurations is closely associated with anesthetically induced unconsciousness, and shows promise as a basis for a new consciousness monitoring system during general anesthesia. Hum Brain Mapp 38:4980-4995, 2017. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: In consciousness or anesthesia studies, pinpointing the precise moment of consciousness or anesthetic transition has been challenging because of the variable lag time between a treatment and its induced response. Here, we describe a novel behavioral method, a forced walking test, which pinpoints the moment of the anesthetic-induced loss of motion (LOM) without handling the animals manually. The mouse is forced to walk on a treadmill, and an anesthetic drug is administered into the peritoneum via a previously secured injection route. The physical activity and the angle of head posture are tracked using a motion sensor preinstalled on the animal''s head. The moments of LOM and recovery of motion (ROM) are identified from the physical activity parameters obtained by the sensor. Comparison of our method with the conventional loss-of-righting-reflex assay showed that the time point of LOM was not significantly different between the two methods when examined with two different types of anesthetic agents, propofol and ketamine/xylazine cocktail. In addition, the electrophysiological signals simultaneously acquired in the cortex and the thalamus of the mouse during the forced walking test showed that the brain rhythms induced by ketamine/xylazine anesthesia were generated and terminated in a time-locked manner with respect to LOM and ROM, respectively. In conclusion, the forced walking test allows an objective and precise detection of anesthetic-induced LOM, as well as ROM during awakening from anesthesia, in test animals. [Copyright &y& Elsevier]

Abstract: Frontoparietal connectivity has been suggested to be important in conscious processing and its interruption is thought to be one mechanism of general anesthesia. Data in animals demonstrate that feedforward processing of information may persist during the anesthetized state, while feedback processing is inhibited. We investigated the directionality and functional organization of frontoparietal connectivity in 10 human subjects anesthetized with propofol on two separate occasions. Multichannel electroencephalography and a computational method of assessing directed functional connectivity were employed. We demonstrate that directed feedback connectivity is diminished with loss of consciousness and returns with responsiveness to verbal command. We also applied the Dendrogram classification method to assess the global organization of directed functional connectivity during consciousness and anesthesia. We demonstrate a state-specific hierarchy and subject-specific subhierarchy in functional organization. These data support the hypothesis that specific states of human consciousness are defined by specific states of frontoparietal connectivity. [Copyright &y& Elsevier]

Abstract: The cognitive unbinding paradigm suggests that the synthesis of neural information is attenuated by general anesthesia. Here, we analyzed the functional organization of brain activities in the conscious and anesthetized states, based on functional segregation and integration. Electroencephalography (EEG) recordings were obtained from 14 subjects undergoing induction of general anesthesia with propofol. We quantified changes in mean information integration capacity in each band of the EEG. After induction with propofol, mean information integration capacity was reduced most prominently in the γ band of the EEG (p =.0001). Furthermore, we demonstrate that loss of consciousness is reflected by the breakdown of the spatiotemporal organization of γ waves. We conclude that induction of general anesthesia with propofol reduces the capacity for information integration in the brain. These data directly support the information integration theory of consciousness and the cognitive unbinding paradigm of general anesthesia. [Copyright &y& Elsevier]

Ketamine and propofol have distinctively different molecular mechanisms of action and neurophysiological features, although both induce loss of consciousness. Therefore, identifying a common feature of ketamine- and propofol-induced unconsciousness would provide insight into the underlying mechanism of losing consciousness. In this study we search for a common feature by applying the concept of type-II complexity, and argue that neural complexity is essential for a brain to maintain consciousness. To test this hypothesis, we show that complexity is suppressed during loss of consciousness induced by ketamine or propofol. We analyzed the randomness (type-I complexity) and complexity (type-II complexity) of electroencephalogram (EEG) signals before and after bolus injection of ketamine or propofol. For the analysis, we use Mean Information Gain (MIG) and Fluctuation Complexity (FC), which are information-theory-based measures that quantify disorder and complexity of dynamics respectively. Both ketamine and propofol reduced the complexity of the EEG signal, but ketamine increased the randomness of the signal and propofol decreased it. The finding supports our claim and suggests EEG complexity as a candidate for a consciousness indicator. [ABSTRACT FROM AUTHOR]