Impact of age on the reliability of GE Entropy™ module indices for guidance of maintenance of anaesthesia in adult patients: a single-centre retrospective analysis

Background: The GE Entropy™ module uses frontal EEG to compute the processed indices state entropy (SE), response entropy (RE), and burst suppression ratio (BSR) to guide maintenance of anaesthesia by supposedly minimising overly ‘deep’ or ‘light’ anaesthesia. It remains unclear whether the manufacturer-recommended index ranges accurately reflect anaesthesia levels or prevent complications such as burst suppression or arousal reactions. Methods: We retrospectively analysed 15 608 patient records, evaluating 14 770 adult patients (18–90 yr old) undergoing general anaesthesia. Age-dependent effects on processed index values were assessed using linear regression and Spearman's correlation coefficients (rho). Results: During steady-state anaesthesia (BSR=0), only 38.4% (32.5–42.4%) of SE values were within the recommended range, with most values below the target. Age was positively associated with an increase in age-adjusted minimal alveolar concentration for volatile anaesthetics (adjusted [adj.] R²=0.18, P<0.001, rho=0.47 [0.20–0.70]). Despite this, SE paradoxically increased with age (adj. R²=0.45, P<0.001, rho=0.67 [0.51–0.79]). This trend persisted even during periods with positive BSR despite supposedly adequate SE values (adj. R²=0.73, P<0.001, rho=0.90 [0.80–0.95]). Maintaining anaesthesia within the recommended index range did not prevent positive BSR. Additionally, both frequency (adj. R²=0.70, P<0.001, rho=0.92 [0.85–0.95]) and duration (adj. R²=0.73, P<0.001, rho=0.89 [0.82–0.93]) of ΔRE-SE≥10, indicating arousal, increased with age. Conclusions: Despite their intuitive appeal, the processed EEG index values SE, RE, ΔRE-SE, and BSR showed limited reliability in guiding maintenance of anaesthesia, especially in older patients. Anaesthesiologists should not rely exclusively on the recommended index value range, as it is often unattainable and does not prevent burst suppression or arousal indicators.