Bispectral index values, sedation-agitation scores, and plasma Lorazepam concentrations in critically ill surgical patients.

Background: Publications on the use of the bispectral index for sedation monitoring in the intensive care unit are increasing. However, few studies have involved correlation of bispectral index with serum drug concentrations.

Objectives: To assess the degree of correlation between bispectral index values, scores on the Sedation-Agitation Scale, and steady-state serum concentrations of lorazepam.

Methods: A prospective open-label study of patients in a surgical intensive care unit who were receiving mechanical ventilation and continuous infusions of lorazepam for more than 24 hours. Bispectral index was measured (BIS-XP, Aspect Medical, Norwood, Massachusetts) to assess patients' sedation. Sensors were applied and values recorded before and after stimulation (endotracheal suctioning). Concomitant plasma samples were obtained to measure lorazepam concentration and scores on the Sedation-Agitation Scale were recorded.

Results: Sixteen patients were studied. Correlations between plasma concentrations of lorazepam and measurements of bispectral index for 1, 2, and 3 minutes before endotracheal stimulation were poor (0.21, 0.29, and 0.25, respectively). Correlation of peak values for bispectral index (after stimulation) with plasma concentrations of lorazepam was 0.29. Correlations of scores on the Sedation-Agitation Scale with the aforementioned values for bispectral index were similarly poor. Area under the curve for bispectral index values also correlated poorly with plasma concentration of lorazepam (0.19) and score on the Sedation-Agitation Scale (0.10).

Conclusions: The correlation between bispectral index and score on the Sedation-Agitation Scale was poor. Correlation between bispectral index and plasma concentration of lorazepam was modestly better, but insufficient for clinical utility.