The bispectral index (BIS) monitor measures processed EEG signals to assess depth of anaesthesia. A BIS value of 40–60 corresponds to which clinical state?
- A Awake, alert state
- B Light sedation/anxiolysis
- C General anaesthesia (low probability of recall) ✓
- D Deep anaesthesia approaching burst suppression
Correct answer: C. General anaesthesia (low probability of recall)
Explanation
The BIS scale runs from 0 (isoelectric EEG, brain death) to 100 (fully awake). A target of 40–60 represents an adequate depth for general anaesthesia, minimizing the probability of intraoperative awareness while avoiding excessive anaesthetic depth. Values of 60–80 indicate moderate sedation, 80–100 indicate an awake state, and values below 40 indicate deep anaesthesia with increasing risk of burst suppression. The BIS monitor has been shown to reduce intraoperative awareness and to guide anaesthetic agent titration effectively.
Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.