Bispectral Index (BIS): Interpreting Depth of Anesthesia

The Bispectral Index (BIS) is an electroencephalogram (EEG)-derived parameter used to assess the depth of sedation and anesthesia. It provides a numerical value that helps guide anesthetic dosing, minimize awareness, and avoid excessive anesthetic depth.

BIS values range from 0 to 100, with higher numbers reflecting greater levels of consciousness.

BIS Scale Interpretation

A BIS value of 100 represents a fully awake and alert patient with normal cortical activity.

A BIS value around 70 corresponds to moderate sedation, where the patient may be drowsy but can still respond to verbal stimulation.

A BIS range of 40 to 60 indicates an adequate hypnotic state for general anesthesia, associated with a low risk of intraoperative awareness and appropriate suppression of cortical activity.

Values below this range suggest excessively deep anesthesia and may be associated with delayed emergence and increased risk of hemodynamic instability.

Clinical Significance

BIS monitoring is commonly used to:

Titrate anesthetic agents during general anesthesia
Reduce the risk of intraoperative awareness
Avoid unnecessarily deep anesthesia
Guide sedation during monitored anesthesia care (MAC)

While BIS is a useful adjunct, it should always be interpreted in conjunction with clinical signs and hemodynamic parameters, rather than as a standalone measure.