Changes in Alpha Frequency and Power of the Electroencephalogram during Volatile-Based General Anesthesia.

Darren Hight,Logan J Voss,Jamie Sleigh,Paul S Garcia

doi:10.3389/fnsys.2017.00036

Darren Hight, Logan J Voss + Show 2 more

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https://doi.org/10.3389/fnsys.2017.00036

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Abstract

Oscillations in the electroencephalogram (EEG) at the alpha frequency (8–12 Hz) are thought to be ubiquitous during surgical anesthesia, but the details of how this oscillation responds to ongoing changes in volatile anesthetic concentration have not been well characterized. It is not known how often alpha oscillations are absent in the clinical context, how sensitively alpha frequency and power respond to changes in anesthetic concentration, and what effect increased age has on alpha frequency. Bipolar EEG was recorded frontally from 305 patients undergoing surgery with sevoflurane or desflurane providing general anesthesia. A new method of detecting the presence of alpha oscillations based on the stability of the rate of change of the peak frequency in the alpha range was developed. Linear concentration-response curves were fitted to assess the sensitivity of alpha power and frequency measures to changing levels of anesthesia. Alpha oscillations were seen to be inexplicably absent in around 4% of patients. Maximal alpha power increased with increasing volatile anesthetic concentrations in half of the patients, and decreased in the remaining patients. Alpha frequency decreased with increasing anesthetic concentrations in near to 90% of patients. Increasing age was associated with decreased sensitivity to volatile anesthesia concentrations, and with decreased alpha frequency, which sometimes transitioned into the theta range (5–7 Hz). While peak alpha frequency shows a consistent slowing to increasing volatile concentrations, the peak power of the oscillation does not, suggesting that frequency might be more informative of depth of anesthesia than traditional power based measures during volatile-based anesthesia. The alpha oscillation becomes slower with increasing age, even when the decreased anesthetic needs of older patients were taken into account.

Highlights

Oscillations in the human electroencephalogram (EEG) in the alpha frequency band (8–12 Hz) were first reported by Berger (1929) in awake subjects
Despite much being known about alpha during anesthesia, some key questions that have import on our understanding of how anesthetics modulate cortical networks still remain unanswered; how often does alpha occur in the clinical context, how does alpha frequency and power respond to changes in anesthetic concentration, and what is the effect of increased age on alpha frequency and power?
A frontal alpha oscillation under anesthesia was inexplicably absent in around 4% of our patients

Summary

Introduction

Oscillations in the human electroencephalogram (EEG) in the alpha frequency band (8–12 Hz) were first reported by Berger (1929) in awake subjects. Alpha oscillations were observed during sedation, sleep and anesthesia (Gibbs et al, 1937). Much is known about the alpha oscillation during anesthesia The alpha oscillation of anesthesia is thought to have a similar biological origin as sleep-spindles, namely that it results from synchronized volleys of neural bursts in the thalamocortical system (Steriade et al, 1993). As the rate of neural volleys is dependent on the level of neuronal membrane hyperpolarization (Hughes and Crunelli, 2005), the frequency of an alpha oscillation is thought to represent the degree of inhibition in the thalamocortical system (Sleigh et al, 2011). Despite much being known about alpha during anesthesia, some key questions that have import on our understanding of how anesthetics modulate cortical networks still remain unanswered; how often does alpha occur in the clinical context, how does alpha frequency and power respond to changes in anesthetic concentration, and what is the effect of increased age on alpha frequency and power?

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