Comorbidity-dependent changes in alpha and broadband electroencephalogram power during general anaesthesia for cardiac surgery

Abstract

Background: Age and comorbidities are reported to induce neurobiological transformations in the brain. Whilst the influence of ageing on anaesthesia-induced electroencephalogram (EEG) changes has been investigated, the effect of comorbidities has not yet been explored. We hypothesised that certain diseases significantly affect frontal EEG alpha and broadband power in cardiac surgical patients. Methods: We analysed the frontal EEGs of 589 patients undergoing isoflurane general anaesthesia from a prospective observational study. We used multi-and uni-variable regression to analyse the relationships between comorbidities and age as independent with peak and oscillatory alpha, and broadband power as dependent variables. A score of comorbidities and minimum alveolar concentration (MAC) was built to interrogate the combined effect of age and score on alpha and broadband power. Results: At the univariable level, many comorbidities were associated with lower EEG alpha or broadband power. Multivariable regression indicated the independent association of numerous comorbidities and MAC with peak alpha (R 2 ¼0.19) and broadband power (R 2 ¼0.31). The association with peak alpha power is markedly reduced when the underlying broadband effect is subtracted (R 2 ¼0.09). Broadband measures themselves are more strongly correlated with comorbidities and MAC (R 2 ¼0.31) than age (R 2 ¼0.15). Conclusions: Comorbidities and age are independently associated with decreasing frontal EEG alpha and broadband power during general anaesthesia. For alpha power, the association is highly dependent on the underlying broadband effect. These findings might have significant clinical consequences for automated computation for depth of anaesthesia in comorbid patients, because misclassification might pose the risk of under-or over-dosing of anaesthetics. Clinical trial registration: NCT02976584.

Brain activity complexity has a nonlinear relation to the level of propofol sedation

“…1,2 However, spectral modulations of the EEG signal are strongly dependent on the anaesthetic used 3,4 and patient age, 5,6 among other factors. 7 In contrast, current theories of consciousness, such as the integrated information theory 8,9 and the global neuronal workspace theory, 10,11 emphasise information as a key aspect of the neural basis of consciousness. Be it the amount of integrated information in cortical circuits or the global availability of information, these theories propose that the causal informational relations between neuronal elements, rather than specific oscillations, are the key biological aspect of brain functioning that define states of consciousness such as wakefulness or anaesthesia.…”

Neuromonitoring and Neurocognitive Outcomes in Cardiac Surgery: A Narrative Review

“…174 However, alpha power can be altered by comorbid conditions in cardiac surgical patients under general anesthesia, with profound implications for its use in guiding depth of hypnosis. 175 Similarly, elderly patients, who represent a sizeable proportion of cardiac surgical patients, often display reduced frontal alpha power under anesthesia, which can lead to misinterpretation of depth of anesthesia. 141…”

Peri‐operative neurological monitoring with electroencephalography and cerebral oximetry: a narrative review

“…Lower alpha power under anaesthesia is seen in patients with more comorbidities and impaired pre-operative neurocognitive function [25,26]. To take this relationship further, it has also been shown that patients with lower alpha power are more prone to developing burst suppression during anaesthesia [27].…”

“…The EEG response under anaesthesia has been proposed as a marker of brain health as other age‐independent factors also affect the size of the alpha power. Lower alpha power under anaesthesia is seen in patients with more comorbidities and impaired pre‐operative neurocognitive function [25, 26]. To take this relationship further, it has also been shown that patients with lower alpha power are more prone to developing burst suppression during anaesthesia [27].…”