Clinical Electroencephalography for Anesthesiologists

Abstract

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.

Optogenetic activation of dopamine neurons in the ventral tegmental area induces reanimation from general anesthesia

“…The slow oscillations modulate the alpha oscillations (7) and phaselimited spiking activity (8). Propofol's simultaneous actions in the cortex, thalamus, and in several brainstem nuclei contribute to these dynamics (2,6,8,9). Less research has been done on the neurophysiology of emergence from general anesthesia.…”

“…Traditionally, studies of the mechanisms of general anesthesia have focused on characterizing the actions of anesthetic drugs at molecular targets (4). Recent studies have begun to characterize how anesthetics act at specific neural circuits to create altered states of arousal (2,3,5,6). For example, the anesthetic propofol impairs intracortical and thalamocortical communication by inducing coherent alpha and incoherent slow oscillations (7,8).…”

Monitoring the brain strikes a discordant note for anesthesiologists

“…• 20,21 Au fur et à mesure que nous en saurons plus sur l'anesthésie générale, du niveau moléculaire jusqu'au niveau des neurosciences sur le système, [22][23][24] nous pourrons concevoir une nouvelle génération de moniteurs cérébraux avec disposant de bases scientifiques toujours plus solides qui refléteront plus précisément les différents états neurologiques et les profondeurs de l'anesthésie.…”

“…3 To this end, there are useful online educational resources 18,19 and informative journal articles. 20,21 As we learn more about general anesthesia, from the molecular to the systems neuroscience level, [22][23][24] we will be able to design a new generation of brain monitors with everstronger scientific foundations that will accord more accurately with different neurological states and depths of anesthesia.…”

General Anesthesia and Sleep

“…Regarding the nature of unconsciousness at surgical level, different agents (i.e. propofol, sevoflurane, ketamine and dexmedetomidine), curiously, elicit unique EEG signatures, presumably attributed to pharmacological interruption of select neuronal circuits [3]. The circuits that are associated with sleep/arousal, which are photo-entrained, reveal rhythmicity and may continue to clock-on independently of the anesthesia-interrupted circuits.…”