Bispectral Index (BIS) monitoring is being used during TIVA with propofol. The BIS value suddenly increases from 40 to 72 despite an unchanged propofol infusion rate. Which is the MOST likely explanation?

• A Propofol infusion rate is too high, causing deep anaesthesia
• B The rise in BIS reflects increased surgical stimulation and is a normal response
• C BIS probe failure; the value cannot be trusted at levels above 60
• D Patient may be becoming aware; check propofol infusion integrity and consider increasing dose ✓

Explanation

A BIS value of 40–60 indicates an adequate depth of anaesthesia for surgery. A sudden rise to 72 (awake range 90–100; sedation 60–80; general anaesthesia 40–60) suggests lightening of anaesthesia and potential risk of intraoperative awareness. The anaesthesiologist should immediately check for propofol pump disconnection, occlusion, or syringe error; check TIVA infusion line patency; and consider bolusing additional propofol and increasing the infusion rate. BIS-guided TIVA has been shown to reduce the incidence of awareness (B-Aware trial). BIS is unreliable with ketamine (may show low BIS despite consciousness) but valid for propofol TIVA.

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

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Written and medically reviewed by the StethoPrep medical team.