Question

A 40 year old female underwent surgery. Postoperatively she told the anaesthetist that she was aware of operative events and was very uncomfortable about it. Intraoperative awareness is best evaluated (to prevent such instances) by?

• A. Pulse oximetry
• B. Colour Doppler
• C. Bispectral index
• D. End tidal carbon dioxide

Hint:

You need a processed-EEG monitor of depth of anaesthesia, not oxygenation or ventilation.

Answer 1

The Correct Option is C

Step 1: The clinical problem is intraoperative awareness, i.e. inadequate depth of anaesthesia letting the patient perceive and recall events. We need a monitor of depth of anaesthesia (level of consciousness).
Step 2: The Bispectral index (BIS) is a processed EEG-derived number from 0 to 100 that reflects the hypnotic component / depth of anaesthesia. A target of roughly 40 to 60 indicates adequate general anaesthesia and reduces the risk of awareness.
Step 3: Reviewing the alternatives: pulse oximetry measures oxygen saturation and pulse, not depth; colour Doppler is a vascular/blood-flow imaging tool unrelated to anaesthetic depth; end tidal carbon dioxide monitors ventilation and circuit integrity, not consciousness.
Step 4: Hence the appropriate monitor to detect and prevent intraoperative awareness is the Bispectral index.
Conclusion: The correct answer is Bispectral index (option 3), matching the printed key.