Associations between anaesthetic dose-adjusted intraoperative EEG alpha power, processing speed, and postoperative delirium: analysis of data from three prospective studies.

BACKGROUND: We previously have shown that low intraoperative EEG alpha power is associated with impaired preoperative cognition, a delirium risk factor, and that intraoperative anaesthetic-dose-adjusted EEG bispectral index values were associated with a four-fold increased risk of postoperative delirium (POD). Yet, associations between intraoperative anaesthetic-dose-adjusted alpha power and delirium or delirium risk factors have yet to be quantified. METHODS: We examined cerebrospinal fluid (CSF) Alzheimer's disease (AD)-related biomarkers, cognitive scores, EEG recordings, and delirium data from 82 noncardiac, non-neurologic surgical patients ≥60 yr in age. Based on prior work, each participant's intraoperative frontoparietal EEG alpha power was anaesthetic dose-adjusted by dividing it by (2.5 minus the age-adjusted end-tidal minimum alveolar concentration), and then analysed for its association with POD and delirium risk factors, preoperative CSF AD-related biomarkers, and preoperative cognition. RESULTS: Lower anaesthetic-dose-adjusted frontoparietal alpha power was associated with increased odds of POD (odds ratio [95% confidence interval (CI)]: 1.44 [1.09, 1.89], P=0.009) and moderate-to-severe delirium (odds ratio [95% CI]: 1.44 [1.04, 2.00], P=0.030). Anaesthetic-dose-adjusted frontoparietal alpha power was not associated with pathologic concentrations of CSF pTau-181, Aβ1-42, or pTau-181/Aβ1-42 (P>0.05). In multivariable cognitive models, anaesthetic-dose-adjusted frontoparietal alpha power was associated with preoperative timed processing speed/executive function performance (β [95% CI]: 0.27 [0.06, 0.49], P=0.014), but not with untimed attention/memory performance (β [95% CI]: 0.12 [-0.13, 0.37], P=0.349). CONCLUSIONS: Lower intraoperative anaesthetic-dose-adjusted frontoparietal alpha power was associated with delirium and delirium-predisposing factors (impaired preoperative processing speed/executive function in timed attention tasks). Larger studies are warranted to confirm these associations after further adjustment for covariates.

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