Combining Observational and Physiologic Sedation Assessment Tools

Purpose: This study was designed to test the hypothesis that bispectral index (BIS) monitoring, when used as an adjunct to current sedation assessment, reduces the amount of sedation used. Background/Significance: ICU patients frequently experience episodes of oversedation. A wide array of sedation scales have been proposed and tested with varying results. There is some confusion about BIS monitoring both in literature and practice; BIS is neither adequate, nor designed, to replace observational assessments of the patient's response to sedation. This study is unique in that it explores how a specific outcome variable (the amount of sedation) is impacted by augmenting (not replacing) current methods of sedation assessment. Methods: This prospective randomized controlled trial blinded nurses to the primary purpose of the study. Following informed consent by the subject's legally authorized representative, for this institutional review board approved study, 51 subjects were randomized to receive sedation assessment with either the standard of care alone (Ramsay-alone group; n = 25), or the standard of care plus BIS (BIS-augmentation group; n = 26). The study period began at 8:00 a.m. on the day of study and lasted 12 hours. Nurses were instructed to adjust sedation to a Ramsay score of 4 (both groups) and a BIS value between 60 and 70 (BIS-augmentation group). Results: The results represent data from 51 subjects included in the interim analysis of a planned enrollment of 90 subjects. The interim analysis was performed using a significance level of .025 to explore the primary research question. Upon rejecting the null hypothesis for the primary research question, the remaining research questions were explored using a significance level of .05. Data were analyzed using SAS v9.1 (Cary, NC). The mean infused volumes for the Ramsay-alone group (175.36 ml) and the BIS-augmentation group (97.51 ml) were significantly different (F=6.00, p=.018, r2=.011). The mean infusion rates for the Ramsay-alone group (30.19 mcg/kg/min) and BIS-augmentation group (15.35 mcg/kg/min) were significantly different (F=8.63, p=.005, r2=.15). The length of time for subjects in the Ramsay-alone group (9.47 minutes) compared to the BIS-augmentation group (1.44 minutes) to awaken (recovery rate) when the sedation was discontinued was significantly different (F=24.48, p<.0001). There were no undersedation events reported in either group. Conclusions: BIS augmentation of current observational assessment resulted in a reduction in the sedation use and a shorter time to recovery from sedation; no increase in undersedation associated with the reduced use of sedation in the BIS augmented group. Physiologic sedation assessment tools with EEG-derived parameters such as BIS provide useful information that may decrease the incidence of oversedation in critically ill patients.