Do Complexity Measures of Frontal EEG Distinguish Loss of Consciousness in Geriatric Patients Under Anesthesia?

Sarah L Eagleman,Nicholas T Ouellette,Mark S Cohen,David R Drover,M Bruce Maciver,Don A Vaughn,Caitlin M Drover

doi:10.3389/fnins.2018.00645

Abstract

While geriatric patients have a high likelihood of requiring anesthesia, they carry an increased risk for adverse cognitive outcomes from its use. Previous work suggests this could be mitigated by better intraoperative monitoring using indexes defined by several processed electroencephalogram (EEG) measures. Unfortunately, inconsistencies between patients and anesthetic agents in current analysis techniques have limited the adoption of EEG as standard of care. In attempts to identify new analyses that discriminate clinically-relevant anesthesia timepoints, we tested 1/f frequency scaling as well as measures of complexity from nonlinear dynamics. Specifically, we tested whether analyses that characterize time-delayed embeddings, correlation dimension (CD), phase-space geometric analysis, and multiscale entropy (MSE) capture loss-of-consciousness changes in EEG activity. We performed these analyses on EEG activity collected from a traditionally hard-to-monitor patient population: geriatric patients on beta-adrenergic blockade who were anesthetized using a combination of fentanyl and propofol. We compared these analyses to traditional frequency-derived measures to test how well they discriminated EEG states before and after loss of response to verbal stimuli. We found spectral changes similar to those reported previously during loss of response. We also found significant changes in 1/f frequency scaling. Additionally, we found that our phase-space geometric characterization of time-delayed embeddings showed significant differences before and after loss of response, as did measures of MSE. Our results suggest that our new spectral and complexity measures are capable of capturing subtle differences in EEG activity with anesthesia administration—differences which future work may reveal to improve geriatric patient monitoring.

Highlights

About 50% of geriatric patients aged 65 and older will require anesthesia for a surgical procedure at some time in their remaining years (Kim et al, 2015)
Several investigators have suggested that geriatric patients may benefit from maintenance at lighter anesthetic levels (Lindholm et al, 2009; Kalkman et al, 2011; Strøm et al, 2014; Petsiti et al, 2015), which may reduce the risks of developing dementia (Chen et al, 2014)
We have demonstrated the first observation of a change in 1/f frequency scaling in EEGs in an anesthesia protocol. 1/f frequency scaling was sensitive to before and after LOR

Summary

Introduction

About 50% of geriatric patients aged 65 and older will require anesthesia for a surgical procedure at some time in their remaining years (Kim et al, 2015). It has been suggested that geriatric patients have an increased risk of dementia, delirium, and neurocognitive dysfunction after exposure to anesthetic agents (Avidan and Evers, 2011; Chen et al, 2013; Strøm et al, 2014; Purdon et al, 2015a; Yang and Fuh, 2015). Given this potential risk, several investigators have suggested that geriatric patients may benefit from maintenance at lighter anesthetic levels (Lindholm et al, 2009; Kalkman et al, 2011; Strøm et al, 2014; Petsiti et al, 2015), which may reduce the risks of developing dementia (Chen et al, 2014). There would be tremendous advantage in the ability to titrate an anesthetic dose accurately to balance an improved medical outcome against the risk of intraoperative awareness

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Discussion

Conclusion