Impact of Interscalene Block Combined With General Anesthesia on Burst Suppression in Shoulder Surgery Patients

Burst Suppression Ratio (BSR): The main quantitative indicator of deep cortical suppression, calculated as the percentage of time the EEG signal remained in a suppression state (defined as amplitude <±10 μV for ≥0.5 seconds) during surgery. BSR was recorded continuously and analyzed across four perioperative phases (Phase 0-3).

The average spectral power (μV²) of EEG signals was analyzed for four conventional frequency bands-delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), and beta (13-30 Hz)-using FFT-based spectral analysis. These values were calculated from frontal electrodes (Fp1, Fp2, F7, F8), and comparisons were made between Group B (ISB group) and Group K (control group) at each phase.

The Patient State Index (PSI), a proprietary quantitative measure ranging from 0 to 100, is derived from multichannel electroencephalogram (EEG) signals using the SedLine® brain function monitoring system. Higher PSI values indicate lighter levels of anesthesia or increased cortical activity, whereas lower values correspond to deeper anesthetic states. In this study, PSI values were utilized to monitor the level of consciousness and cortical stability during the intraoperative period. Particular emphasis was placed on PSI trends observed during Phase 1 (following the administration of the interscalene block but prior to the induction of general anesthesia), in order to investigate any pre-anesthetic central nervous system effects attributable to the regional block.

Intraoperative mean arterial pressure (MAP) was continuously monitored and recorded at predefined intervals throughout the procedure. Particular attention was paid to measurements taken during anesthesia induction, surgical positioning in the beach chair position, and skin incision. These data were analyzed to evaluate hemodynamic stability and to investigate the potential sympatholytic effects of the interscalene brachial plexus block (ISB).

Total doses of intraoperative sevoflurane, remifentanil, and propofol were recorded for each patient. Volatile anesthetic consumption was quantified in minimum alveolar concentration-hours (MAC-h). The aim was to evaluate whether ISB reduced the requirement for hypnotic and opioid agents during surgery.

Postoperative pain intensity was assessed using the Numerical Rating Scale (NRS), which ranges from 0 (no pain) to 10 (worst imaginable pain). Higher scores indicate greater pain severity. Pain scores were recorded during the post-anesthesia care unit (PACU) stay, specifically within the first two hours following surgery, to evaluate early postoperative analgesia.

The Nursing Delirium Screening Scale (NU-DESC) is a validated, nurse-administered tool used to detect signs of postoperative delirium. It assesses five domains: disorientation, inappropriate behavior, inappropriate communication, illusions/hallucinations, and psychomotor retardation. Each domain is scored from 0 to 2, resulting in a total score ranging from 0 to 10. A total score of ≥2 indicates a high probability of delirium. In this study, NU-DESC scores were recorded during the early postoperative period to identify any acute cognitive changes.

Heart rate (HR) was continuously monitored intraoperatively and recorded at specified time points, with focused analysis during key phases such as anesthesia induction, patient positioning (beach chair position), and surgical incision. Group comparisons were made to assess ISB-associated modulation of cardiac autonomic response.

Peripheral oxygen saturation (SpO₂) was monitored continuously during surgery and recorded at predetermined intervals. Measurements during critical phases, including induction, positioning, and incision, were evaluated to ensure adequate oxygenation and assess any indirect effects of ISB on respiratory function.