Changes in topographic electroencephalogram during deepening levels of propofol sedation based on alertness/sedation scale under bispectral index guidance

Background
Sedation has been associated with numerous changes on electroencephalogram (EEG) but there is a need to clarify specific alterations in relation to deepening levels of sedation with different agents. We aimed to evaluate the effect of deepening levels of sedation induced by propofol and how they compare to natural sleep.

Methods
Fifty consecutive neurologically normal patients who underwent upper gastrointestinal endoscopy while sedated with propofol were included. Topographic EEG spectral maps and the bispectral index (BIS) values were obtained at four time points: wakefulness, mild sedation, deep sedation and recovery. Observer’s Assessment of Alertness and Sedation (OAA/S) score was used to assess sedation levels.

Results
Propofol induced increased delta (0.5–3.5 Hz) and gamma (25–40 Hz) power throughout sedation. In addition, there was decreased alpha power (9–11.5 Hz) in the occipital area and increased global beta (12–25 Hz)/gamma (25–40 Hz) power during mild sedation. Deep sedation was associated with increased theta (4–7 Hz)/alpha (9–11.5 Hz)/beta (12–25 Hz) power, which was maximal frontally.

Conclusion
There are distinct changes associated with deepening levels of propofol induced sedation that distinguish it from natural sleep. This suggests that different mechanisms are involved in them and warrants further investigations to clarify the nature of these changes.