How Electroencephalography Serves the Anesthesiologist

Abstract

Major clinical endpoints of general anesthesia, such as the alteration of consciousness, are achieved through effects of anesthetic agents on the central nervous system, and, more precisely, on the brain. Historically, clinicians and researchers have always been interested in quantifying and characterizing those effects through recordings of surface brain electrical activity, namely electroencephalography (EEG). Over decades of research, the complex signal has been dissected to extract its core substance, with significant advances in the interpretation of the information it may contain. Methodological, engineering, statistical, mathematical, and computer progress now furnishes advanced tools that not only allow quantification of the effects of anesthesia, but also shed light on some aspects of anesthetic mechanisms. In this article, we will review how advanced EEG serves the anesthesiologist in that respect, but will not review other intraoperative utilities that have no direct relationship with consciousness, such as monitoring of brain and spinal cord integrity. We will start with a reminder of anesthestic effects on raw EEG and its time and frequency domain components, as well as a summary of the EEG analysis techniques of use for the anesthesiologist. This will introduce the description of the use of EEG to assess the depth of the hypnotic and anti-nociceptive components of anesthesia, and its clinical utility. The last part will describe the use of EEG for the understanding of mechanisms of anesthesia-induced alteration of consciousness. We will see how, eventually in association with transcranial magnetic stimulation, it allows exploring functional cerebral networks during anesthesia. We will also see how EEG recordings during anesthesia, and their sophisticated analysis, may help corroborate current theories of mental content generation.

Concealed, Unobtrusive Ear-Centered EEG Acquisition: cEEGrids for Transparent EEG

“…EEG is extensively used for clinical applications such as epilepsy diagnostics (Noachtar and Rémi, 2009), sleep staging (Campbell, 2009), diagnosis of hearing loss (Paulraj et al, 2015), anesthesia monitoring (Marchant et al, 2014), and brain-computer interfaces (Shih et al, 2012). Moreover, EEG serves as a fundamental research tool for understanding human brain function (Lopes da Silva, 2013).…”

Automation of anaesthesia: a review on multivariable control

“…These include influence of electromyographic (EMG) activity [5,14,18], electrical or mechanical artifacts from medical devices [23,38,81], time delay [113], specific clinical conditions such as hypovolaemia, hypotension, cerebral ischaemia, hypoglycaemia and hypothermia [23], inter-individual variability of baseline EEG characteristics [68,111] and types of drugs [44]. In addition, opioids may interfere with the EEG-signal during administration of the hypnotic agent [26,50,63,67,84,88] thus rendering the reliability of indices during multidrug administration questionable.…”

“…Each endpoint should be monitored separately and specifically [68]. Validation should be done based on specific drugs.…”

“…Other examples of advanced EEG analysis that may contribute to the problem include Granger causality [28,79], symbolic transfer entropy [52] and permutation entropy [46] [68]. Nonetheless, refinement is necessary for the techniques to be applied in daily practice.…”

MORPhA Scale: behavioral and electroencephalographic validation of a rodent anesthesia scale

“…Alternatively, blood pressure and heart rate evaluation can be considered as fine markers of animal reactivity (sympathetic response to stress) (Smith and Danneman, 2008); these require specific equipment and might be difficult or even impractical in small animals and in certain types of surgeries/interventions (Smith and Danneman, 2008). Electroencephalography (EEG) monitoring, provides the most direct readout of anesthesia effect (Marchant et al, 2014). Indeed, electrophysiological correlates of commonly used behavioral outcomes such as righting reflex (MacIver and Bland, 2014;Pal et al, 2015) or paw pinch (Kortelainen et al, 2012) have been described for some drugs.…”