Bispectral Index (BIS) monitoring converts complex EEG activity into a simplified numeric scale that reflects the level of cortical hypnosis during anesthesia. However, BIS must always be interpreted in context with its derived EEG parameters — Signal Quality Index (SQI), Spectral Edge Frequency (SEF), Suppression Ratio (SR), Total Power (TP), and Electromyography (EMG).
These parameters together illustrate whether a change in BIS arises from true cortical suppression or from technical or physiologic artifacts.
This case study examines BIS dynamics in a 36-year-old woman undergoing laparoscopic ovarian cystectomy, focusing on two key anesthetic phases:
Phase 1: Before CO₂ insufflation (baseline steady-state before incision)
Phase 2: After a 5 mL (≈ 50 mg) propofol bolus, followed by incision and pneumoperitoneum
Patient: 36-year-old female, previous thyroidectomy
Procedure: Laparoscopic ovarian cystectomy
Anesthetic technique: Balanced general anesthesia
Monitoring: ECG, NIBP, SpO₂, EtCO₂, anesthetic gas analysis, BIS with SQI, SEF, SR, TP, and EMG.
Timing: Baseline anesthetic depth prior to surgical incision and before propofol bolus administration.
This phase reflects the steady maintenance level of anesthesia before surgical stimulation and before additional hypnotic supplementation.
Although the BIS value of 24 appears low, it coincides with an SQI 72 % and EMG 29 dB, indicating moderate artifact contamination.
SEF 13.8 Hz (upper α–low β range) suggests that much of the recorded activity originates from high-frequency interference rather than cortical excitation.
TP 69 µV² shows preserved EEG energy, confirming that cortical function remains active rather than suppressed (since TP < 20 µV² would indicate isoelectric activity).
SR 0 % supports the absence of burst suppression.
Thus, the BIS reading primarily reflects signal artifact plus moderate hypnotic depth, not excessive anesthesia. The patient remained hemodynamically stable and ready for the subsequent deepening bolus.
References
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Timing: Three minutes after administration of a 5 mL (≈ 50 mg) propofol bolus given to deepen hypnosis before surgical incision and CO₂ insufflation.
