Abstract
Electroencephalographic (EEG) Burst Suppression (BSUPP) is a discontinuous pattern characterized by episodes of low voltage disrupted by bursts of cortical synaptic activity. It can occur while delivering high-dose anesthesia. Current research suggests an association between BSUPP and the occurrence of postoperative delirium in the post-anesthesia care unit (PACU) and beyond. We investigated burst micro-architecture to further understand how age influences the neurophysiology of this pharmacologically-induced state. We analyzed a subset of EEG recordings (n = 102) taken from a larger data set previously published. We selected the initial burst that followed a visually identified “silent second,” i.e., at least 1 s of iso-electricity of the EEG during propofol induction. We derived the (normalized) power spectral density [(n)PSD], the alpha band power, the maximum amplitude, the maximum slope of the EEG as well as the permutation entropy (PeEn) for the first 1.5 s of the initial burst of each patient. In the old patients >65 years, we observed significantly lower (p < 0.001) EEG power in the 1–15 Hz range. In general, their EEG contained a significantly higher amount of faster oscillations (>15 Hz). Alpha band power (p < 0.001), EEG amplitude (p = 0.001), and maximum EEG slope (p = 0.045) all significantly decreased with age, whereas PeEn increased (p = 0.008). Hence, we can describe an age-related change in features during EEG burst suppression. Sub-group analysis revealed no change in results based on pre-medication. These EEG changes add knowledge to the impact of age on cortical synaptic activity. In addition to a reduction in EEG amplitude, age-associated burst features can complicate the identification of excessive anesthetic administration in patients under general anesthesia. Knowledge of these neurophysiologic changes may not only improve anesthesia care through improved detection of burst suppression but might also provide insight into changes in neuronal network organization in patients at risk for age-related neurocognitive problems.
Highlights
Electroencephalographic (EEG) recordings during the perioperative period can help assess a patient’s brain under anesthesia
We present our results as medians with minimum and maximum values or for the power spectral density (PSD) as median and the median absolute deviation
We found no effect of age when comparing YOUNG and premedicated OLD for the relative alpha power [area under the receiver operating curve (AUC) = 0.63 (0.42 0.82)] and spectral entropy (SpEnt) [AUC = 0.39 (0.19 0.61)], but in premedicated OLD, maximum EEG amplitudes were lower [AUC = 0.89 (0.75 1), ‘‘excellent’’ effect] and the maximum slope was flatter [AUC = 0.77 (0.58 0.92), ‘‘acceptable’’ effect]
Summary
Electroencephalographic (EEG) recordings during the perioperative period can help assess a patient’s brain under anesthesia. If exposed to even higher concentrations of the hypnotic agent (i.e., propofol or sevoflurane), the electrical activity of the brain switches from being dominated by slow and moderate frequency oscillations to a discontinuous state characterized by alternating episodes of cortical activity interrupted by epochs of voltage attenuation without oscillations This state is often referred to as burst suppression (BSUPP; Swank and Watson, 1949). The controversy on the subject persists (Shortal et al, 2019; Wildes et al, 2019), as it does for the general relation between EEG-based monitoring and outcome (Berger et al, 2020; García, 2020) This may in part be related to the difficulty in identifying classic burst suppression patterns in vulnerable patients and because the surgical population most affected by postoperative neurocognitive disorders overlap with the population more likely to develop BSUPP. With our findings we can add to the existing knowledge regarding the effects of age on the EEG described for general anesthesia without BSUPP (Schultz et al, 2004; Purdon et al, 2015; Kreuzer et al, 2020), sleep (Carrier et al, 2001), and (relaxed) awake states (Polich, 1997)
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