Learning Objective #1: Understand the difference between objective tools and subjective sedation scales for monitoring sedation level in ICU

Learning Objective #2: Understand how the new tools such as Heart Rate Variability and bispectral Index of EEG apply in ICU for monitoring the sedation level

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Anxiety and agitation of patient are common in the intensive care unit (ICU), thus sedation is required. The intensivists need a reliable tool as a guide to assess the sedation level. The aim of this study is to compare the power spectral analysis of heart rate variability (HRV) with the bispectral index (BIS), the subjective Sedation-Agitation Scale (SAS) and Ramsay Sedation Score (RSS) in assessing sedation level of the critically-ill patients. The changes of respiratory status and hemodynamic parameters of patients before and after continually sedated were also evaluated. 25 surgical ICU patients were enrolled in this study. Patients were divided into two groups under continuous sedation with propofol (1.5 mg/kg/hr) or midazolam (0.1 mg/kg/hr) for 24 hours. An hour of electrocardiogram(EKG) was recorded for heart rate signal analysis before sedation,12th and 24th hour after continuous sedation. The SAS, RSS scores and BIS index were measured simultaneously during EKG recording. The Acute Physiology And Chronic Health Evaluation (APACHE) II score and other routine parameters were also recorded. Under short-term sedation in the ICU, patients in midazolam group represented a deeper sedation level than propofol by both subjective scores and BIS index without significant change in the standard deviation of successive R-R intervals (SDNN) and very low frequency (VLF, 0.004~0.04Hz) power density after 24-hours continuous sedation. However, there were lower SDNN and VLF power density which correlated with the adverse effect of hypotension in the propofol group after 24-hours continuous sedation.. It's difficult to detect subtle decompensations of critically ill patients under continuous sedation. Objective tools provide additional messages for clinical intensivists, even the respiratory and hemodynamic status of the patients were well-maintained. Combination of HRV, BIS and subjective scores may be beneficial for comprehensive monitoring of the sedation level to avoid oversedation and suppression of autonomic modulation in critically-ill patients.