Bispectral Index (BIS) monitoring of anaesthetic depth is based on processing of which signal?

• A Evoked auditory potential latency from midbrain auditory nuclei
• B Near-infrared spectroscopy of cerebral oxyhaemoglobin
• C Spontaneous electromyographic activity from the frontalis muscle
• D Raw EEG signal from frontal electrodes, analysing frequency, amplitude and phase coupling between frequency bands ✓

Explanation

BIS is derived from processing the frontal EEG by analysing three domains: time domain (burst suppression ratio), frequency domain (spectral edge frequency), and bispectral domain (phase coupling between frequency bands — the 'bispectrum' which detects higher-order statistical relationships between frequency components). The resulting dimensionless index (0–100) correlates with depth of anaesthesia: 100 = fully awake; 40–60 = general anaesthesia; <40 = deep anaesthesia with burst suppression. Awareness under anaesthesia is most likely when BIS >60. EMG artefact from frontalis can falsely elevate the BIS reading.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.