[Falsely elevated-bispectral index]

Area of Science:

• Anesthesiology
• Neurophysiology
• Medical Device Technology

Background:

• The Bispectral Index (BIS) is commonly used to monitor anesthetic depth.
• Accurate BIS monitoring is crucial for patient safety during general anesthesia.
• Factors such as electromyographic (EMG) activity and electrical artifacts can interfere with BIS readings.

Observation:

• A case of falsely elevated BIS values (around 70) was observed during isolated-limb chemotherapy under general anesthesia.
• The anesthesia regimen included remifentanil Target Controlled Infusion (TCI), desflurane, and nitrous oxide.
• No residual neuromuscular blockade or clinical signs of awareness were present despite the high BIS.

Findings:

• High BIS values were attributed to significant electromyographic activity and electrical artifacts from extracorporeal circulation machines and tourniquets.
• BIS values returned to expected levels (around 50) post-operatively.
• The patient reported no intraoperative recall, indicating no actual awareness.

Implications:

• This case underscores the limitations of BIS monitoring, particularly its sensitivity to EMG activity and environmental electrical artifacts.
• It emphasizes the importance of identifying and eliminating artifacts before adjusting anesthetic depth.
• A proposed decision algorithm can aid clinicians in managing surprising high BIS readings by considering neuromuscular blockade, clinical response, and potential artifact sources.