Bispectral index (BIS) monitoring is used to assess depth of anaesthesia. A BIS value of 40–60 during maintenance of general anaesthesia corresponds to:
- A Awake, fully conscious state
- B Light sedation/moderate sedation
- C General anaesthesia (low probability of consciousness and recall) ✓
- D Burst suppression/deep anaesthetic coma
Explanation
BIS scale: 100 = fully awake; 80–100 = light sedation; 60–80 = moderate sedation; 40–60 = general anaesthesia with low probability of consciousness/recall; 20–40 = deep hypnosis/burst suppression transition; <20 = burst suppression/isoelectric EEG. Maintaining BIS between 40–60 during surgery optimises the balance between adequate anaesthetic depth (preventing awareness) and excessive depth (prolonging recovery). BIS >60 during surgery correlates with increased risk of intraoperative awareness. BIS-guided anaesthesia has been shown in some trials to reduce volatile agent consumption and speed emergence.
Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.
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Written and medically reviewed by the StethoPrep medical team.