Abstract
Introduction: Bispectral Index is an objective tool to assess electroencephalographic activity and measure the effect of certain sedatives and hypnotics on the brain. In addition, there are certain subjective tools such as the observer's assessment of alertness and sedation which are used. The correlation between BIS and the concentration of propofol in the brain, and the relationship between these subjective and objective tools in assessing sedation levels are the subject of this study.
Methods: Thirty healthy volunteers enrolled in this prospective observational study. They were sedated with a target controlled infusion of propofol with an initial target of 0.8 μg.mL-1 and an increase in target to 0.2 μg.mL-1 ten minutes after equilibration of the predicted and set target concentrations. In each sedation score, the Bispectral Index value and predicted effect site concentration of propofol were recorded and analyzed. Analysis of variance and significant differences between groups were analyzed by paired t-test. Correlations between Bispectral Index and effect site concentration of propofol at each sedation score and the relationship of BIS and effect site concentration of propofol to each sedation score were assessed and analyzed by nonparametric Spearman's rho (ρ).
Results: The means of Bispectral Index and effect site concentration of propofol at each sedation score showed a significant difference with the following score. Additionally, Bispectral Index and effect site concentration of propofol showed a significant negative correlation in sedation scores 3 and 2 when inducing sedation. In other sedation scores or when reversing the sedation, no strong correlation was noted.
Conclusion: Both Bispectral Index and effect site concentration of propofol indicate a good estimate of sedation levels; however their correlations are significant and negative only at moderate and deep sedation levels, and during the induction of sedation.