Effect of interscalene brachial plexus block on eeg dynamics and burst suppression during general anaesthesia for shoulder surgery

Objective: This study aimed to evaluate the effects of combining general anesthesia with an interscalene brachial plexus block (ISB) on electroencephalogram (EEG) parameters and burst suppression ratio (BSR) in patients undergoing shoulder surgery. Methods: Fifty patients scheduled for elective shoulder surgery were enrolled in the study and randomly assigned to either the ISB group (Group B) or the control group without ISB (Group K). All patients received a standardized general anesthesia protocol. Intraoperative EEG recordings were obtained using the SedLine® monitor from Fp1, Fp2, F7, and F8 electrodes. Power spectral densities for delta (0.5–4 Hz), theta (4–8 Hz), alpha (8–12 Hz), and beta (13–30 Hz) frequency bands, along with PSI and BSR values, were analyzed. Results: A statistically significant reduction in delta band power was observed in the ISB group (p < 0.01). Theta power also showed a decreasing trend in this group. Conversely, alpha and beta band powers were elevated, suggesting preserved cortical reactivity. While PSI values were similar between groups, SEF values demonstrated greater stability in the ISB group. Although BSR did not significantly differ, the reduction in delta power and increase in beta activity indicate the preservation of a more physiological EEG pattern. Conclusion: In addition to providing peripheral analgesia, ISB appears to exert central effects on EEG activity by suppressing afferent nociceptive input. These effects are reflected in reduced delta power and preserved alpha-beta activity. The analgesia achieved through ISB may contribute to a more stable cortical activity pattern and potentially offer neurocognitive protection through reduced anesthetic requirements.