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

The Effect of Interscalene Brachial Plexus Block Combined With General Anesthesia on Burst Suppression Ratio in Patients Undergoing Shoulder Surgery

This prospective, randomized, double-blind clinical study aimed to investigate the effects of combining general anesthesia with an interscalene brachial plexus block (ISB) on burst suppression ratio (BSR) and electroencephalographic (EEG) activity in patients undergoing elective shoulder surgery. A total of 50 patients were allocated into two groups: those receiving general anesthesia with ISB (Group B) and those receiving general anesthesia alone (Group K). Intraoperative EEG recordings were obtained from frontal electrodes (Fp1, Fp2, F7, F8) using a SedLine® monitor. Power spectral analysis was conducted for delta, theta, alpha, and beta frequency bands, alongside assessment of Patient State Index (PSI) and BSR.

This prospective, randomized, double-blind clinical trial was conducted to evaluate the neurophysiological effects of combining interscalene brachial plexus block (ISB) with general anesthesia in patients undergoing elective shoulder surgery. The primary objective was to investigate how ISB influences intraoperative burst suppression ratio (BSR) and EEG-derived brain activity, using quantitative parameters such as power spectral densities of frequency bands and Patient State Index (PSI).

A total of 50 ASA I-III patients scheduled for shoulder surgery were randomly assigned into two groups: Group B (general anesthesia + ISB) and Group K (general anesthesia only). Standardized general anesthesia was maintained with sevoflurane in both groups. EEG data were recorded continuously using a SedLine® monitor from frontal electrodes (Fp1, Fp2, F7, F8) during four perioperative phases. Spectral analysis was performed using Fast Fourier Transform (FFT) and Welch's method to quantify power in the delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), and beta (13-30 Hz) bands. BSR was calculated based on the duration of EEG suppression epochs, while PSI and SEF (Spectral Edge Frequency) were recorded continuously.

Inclusion Criteria:

• Patients classified as ASA Physical Status I-III
• Aged between 18 and 65 years
• Scheduled for elective shoulder surgery under general anesthesia, with or without interscalene brachial plexus block

Exclusion Criteria:

• Advanced renal failure
• Advanced hepatic failure
• Body mass index (BMI) > 40 kg/m²
• History of central nervous system disorders
• Diagnosed psychiatric illness
• History of substance abuse
• Known allergy to any of the drugs used in the study
• Refusal to participate or to provide informed consent

Termination Criteria:

• Severe hypotension (mean arterial pressure < 50 mmHg despite treatment)
• Severe bradycardia (heart rate < 40 bpm requiring intervention)
• Profound hypoxia (SpO₂ < 90% despite oxygen support)
• Drug-related allergic reactions