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Abstract Background Beach chair positioning during general anesthesia is associated with a high incidence of cerebral desaturation; poor neurological outcome is a growing concern. There are no published data pertaining to changes in cerebral oxygenation seen with increases in the inspired oxygen fraction or end-tidal carbon dioxide in patients anesthetized in the beach chair position. Furthermore, the effect anesthetic agents have has not been thoroughly investigated in this context. We plan to test the hypothesis that changes in inspired oxygen fraction or end-tidal carbon dioxide correlate to a significant change in regional cerebral oxygenation in anesthetized patients in beach chair position. We will also compare the effects that inhaled and intravenous anesthetics have on this process. Methods/design This is a prospective within-group study of patients undergoing shoulder arthroscopy in the beach chair position which incorporates a randomized comparison between two anesthetics, approved by the Institutional Review Board of the University of Michigan, Ann Arbor. The primary outcome measure is the change in regional cerebral oxygenation due to sequential changes in oxygenation and ventilation. A sample size of 48 will have greater than 80% power to detect an absolute 4-5% difference in regional cerebral oxygenation caused by changes in ventilation strategy. The secondary outcome is the effect of anesthetic choice on cerebral desaturation in the beach chair position or response to changes in ventilation strategy. Fifty-four patients will be recruited, allowing for drop out, targeting 24 patients in each group randomized to an anesthetic. Regional cerebral oxygenation will be measured using the INVOS 5100C monitor (Covidien, Boulder, CO). Following induction of anesthesia, intubation and positioning, inspired oxygen fraction and minute ventilation will be sequentially adjusted. At each set point, regional cerebral oxygenation will be recorded and venous blood gas analysis performed. The overall statistical analysis will use a repeated measures analysis of variance with Tukey’s HSD procedure for post hoc contrasts. Discussion If simple maneuvers of ventilation or anesthetic technique can prevent cerebral hypoxia, patient outcome may be improved. This is the first study to investigate the effects of ventilation strategies on cerebral oxygenation in patients anesthetized in beach chair position. Trial registration NCT01535274

Abstract Background Videolaryngoscopy presents a new approach for the management of the difficult and rescue airway. There is little available evidence to compare the performance features of these devices in true difficult laryngoscopy. Methods A prospective randomized crossover study was performed comparing the performance features of the Macintosh Laryngoscope, Glidescope, Storz CMAC and Storz DCI videolaryngoscope. Thirty anesthesia providers attempted intubation with each of the 4 laryngoscopes in a high fidelity difficult laryngoscopy manikin. The time to successful intubation (TTSI) was recorded for each device, along with failure rate, and the best view of the glottis obtained. Results Use of the Glidescope, CMAC and Storz videolaryngoscopes improved the view of the glottis compared with use of the Macintosh blade (GEE, p = 0.000, p = 0.002, p = 0.000 respectively). Use of the CMAC resulted in an improved view compared with use of the Storz VL (Fishers, p = 0.05). Use of the Glidescope or Storz videolaryngoscope blade resulted in a longer TTSI compared with either the Macintosh (GLM, p = 0.000, p = 0.029 respectively) or CMAC blades (GLM, p = 0.000, p = 0.033 respectively). Conclusions Unsurprisingly, when used in a simulated difficult laryngoscopy, all the videolaryngoscopes resulted in a better view of the glottis than the Macintosh blade. However, interestingly the CMAC was found to provide a better laryngoscopic view that the Storz DCI Videolaryngoscope. Additionally, use of either the Glidescope or Storz DCI Videolaryngoscope resulted in a prolonged time to successful intubation compared with use of the CMAC or Macintosh blade. The use of the CMAC during manikin simulated difficult laryngoscopy combined the efficacy of attainment of laryngoscopic view with the expediency of successful intubation. Use of the Macintosh blade combined expedience with success, despite a limited laryngoscopic view. The limitations of a manikin model of difficult laryngoscopy limits the conclusions for extrapolation into clinical practice.

The integrated information theory (IIT) proposes a quantitative measure, denoted as Φ, of the amount of integrated information in a physical system, which is postulated to have an identity relationship with consciousness. IIT predicts that the value of Φ estimated from brain activities represents the level of consciousness across phylogeny and functional states. Practical limitations, such as the explosive computational demands required to estimate Φ for real systems, have hindered its application to the brain and raised questions about the utility of IIT in general. To achieve practical relevance for studying the human brain, it will be beneficial to establish the reliable estimation of Φ from multichannel electroencephalogram (EEG) and define the relationship of Φ to EEG properties conventionally used to define states of consciousness. In this study, we introduce a practical method to estimate Φ from high-density (128-channel) EEG and determine the contribution of each channel to Φ. We examine the correlation of power, frequency, functional connectivity, and modularity of EEG with regional Φ in various states of consciousness as modulated by diverse anesthetics. We find that our approximation of Φ alone is insufficient to discriminate certain states of anesthesia. However, amulti-dimensional parameter space extended by four parameters related to Φ and EEG connectivity is able to differentiate all states of consciousness. The association of Φ with EEG connectivity during clinically defined anesthetic states represents a new practical approach to the application of IIT, which may be used to characterize various physiological (sleep), pharmacological (anesthesia), and pathological (coma) states of consciousness in the human brain. [ABSTRACT FROM AUTHOR]