Role of the Bispectral Index in Sedation Monitoring in the ICU

Validation of the patient State Index for monitoring sedation state in critically ill patients: a prospective observational study

PURPOSE

The Patient State Index (PSI) is a newly introduced electroencephalogram-based tool for objective and continuous monitoring of sedation levels of patients under general anesthesia. This study investigated the potential correlation between the PSI and the Richmond Agitation‒Sedation Scale (RASS) score in intensive care unit (ICU) patients and established the utility of the PSI in assessing sedation levels.

METHODS

In this prospective observational study, PSI values were continuously monitored via SedLine® (Masimo, Irvine, CA, USA); the RASS score was recorded every 2 h for patients on mechanical ventilation. Physicians and nurses were blinded to the PSI values. Overall, 382 PSI and RASS score sets were recorded for 50 patients.

RESULTS

The PSI score correlated positively with RASS scores, and Spearman's rank correlation coefficient between the PSI and RASS was 0.79 (95% confidence interval [CI]: 0.75‒0.83). The PSI showed statistically significant difference among the RASS scores (Kruskal‒Wallis chi-square test: 242, df = 6, P < 2.2-e16). The PSI threshold for distinguishing light (RASS score ≥ - 2) sedation from deep sedation (RASS score ≤ - 3) was 54 (95% CI: 50-65; area under the curve, 0.92 [95% CI: 0.89‒0.95]; sensitivity, 0.91 [95% CI: 0.86‒0.95]; specificity, 0.81 [95% CI: 0.77-0.86]).

CONCLUSIONS

The PSI correlated positively with RASS scores, which represented a widely used tool for assessing sedation levels, and the values were significantly different among RASS scores. Additionally, the PSI had a high sensitivity and specificity for distinguishing light from deep sedation. The PSI could be useful for assessing sedation levels in ICU patients. University Hospital Medical Information Network (UMIN000035199, December 10, 2018).

Novel insights on association and reactivity of Bispectral Index, frontal electromyogram, and autonomic responses in nociception-sedation monitoring of critical care patients

Background

Assessing nociception and sedation in mechanically ventilated patients in the ICU is challenging, with few reliable methods available for continuous monitoring. Measurable cardiovascular and neurophysiological signals, such as frontal EEG, frontal EMG, heart rate, and blood pressure, have potential in sedation and nociception monitoring. The hypothesis of this explorative study is that derived variables from the aforementioned signals predict the level of sedation, as described by the Richmond Agitation-Sedation score (RASS), and respond to painful stimuli during critical care.

Methods

Thirty adult postoperative ICU patients on mechanical ventilation and receiving intravenous sedation, excluding patients with primary neurological disorders, head injury, or need for continuous neuromuscular blockage. Bispectral Index (BIS), EMG power (EMG), EMG-derived Responsiveness Index (RI), and averaged blood pressure variability (ARV) were tested against RASS measurements. The aforementioned variables together with blood pressure and Surgical Pleth Index (SPI) were explored before and after painful stimuli (for example bronchoscopy, or pleural puncture) at varying RASS levels, to test variable responsiveness.

Results

BIS, EMG, and RI predicted RASS levels with a prediction probability (PK) of 0.776 for BIS, 0.761 for EMG, and 0.763 for RI. In addition, BIS, EMG, and ARV demonstrated responsiveness to painful stimuli during deep sedation (RASS score ≤ -3).

Conclusion

Variables derived from EEG and EMG are associated with sedation levels, as described by the RASS score. Furthermore, these variables, along with ARV, react with consistency to painful stimuli during deep sedation (RASS -5 to -3), offering novel tools for nociception-sedation monitoring of mechanically ventilated ICU patients requiring deep sedation.

Adaptive Sedation Monitoring From EEG in ICU Patients With Online Learning

Sedative medications are routinely administered to provide comfort and facilitate clinical care in critically ill ICU patients. Prior work shows that brain monitoring using electroencephalography (EEG) to track sedation levels may help medical personnel to optimize drug dosing and avoid the adverse effects of oversedation and undersedation. However, the performance of sedation monitoring methods proposed to date deal poorly with individual variability across patients, leading to inconsistent performance. To address this challenge we develop an online learning approach based on Adaptive Regularization of Weight Vectors (AROW). Our approach adaptively updates a sedation level prediction algorithm under a continuously evolving data distribution. The prediction model is gradually calibrated for individual patients in response to EEG observations and routine clinical assessments over time. The evaluations are performed on a population of 172 sedated ICU patients whose sedation levels were assessed using the Richmond Agitation-Sedation Scale (scores between -5 = comatose and 0 = awake). The proposed adaptive model achieves better performance than the same model without adaptation (average accuracies with tolerance of one level difference: 68.76% vs. 61.10%). Moreover, our approach is shown to be robust to sudden changes caused by label noise. Medication administrations have different effects on model performance. We find that the model performs best in patients receiving only propofol, compared to patients receiving no sedation or multiple simultaneous sedative medications.

Minimal alveolar concentration for deep sedation (MAC-DS) in intensive care unit patients sedated with sevoflurane: A physiological study

BACKGROUND

Volatile anaesthetic agents, especially sevoflurane, could be an alternative for sedating ICU patients. In the operating theatre, volatile anaesthetic agents are monitored using minimal alveolar concentration (MAC). In ICU, MAC may be used to assess sedation level and may replace clinical scale especially when they are unusable. Therefore, we sought to investigate the minimal sevoflurane end-tidal concentration to achieved deep sedation in critical ill patients: MAC-deep sedation (MAC-DS).

METHODS

In a prospective interventional study, we included patients with a Richmond Assessment Sedation Score (RASS) of 0 without any sedation. We stepwise increased sevoflurane concentration level before assessing for deep sedation (RASS≤-3). MAC-DS was defined as the minimal sevoflurane MAC fraction or sevoflurane expiratory fraction (FeSevo) to get 90% and 95% of patients in deep sedation (MAC-DS 90 and MAC-DS 95, respectively).

RESULTS

Between June and November 2014, 30 patients were included (median age=60 years [interquartile range: 47-69]). Increasing sevoflurane MAC was correlated with a decrease in RASS values (r=-0.83, P<0.001). MAC-DS 90 and MAC-DS 95 were achieved at 0.42 MAC (CI 95 [0.38-0.46]) and 0.46 MAC (CI 95 [0.42-0.51]), respectively. FeSevo to achieve MAC-DS 90 and MAC-DS 95 was 0.72 (CI 95 [0.65-0.79]) and 0.80 (CI 95 [0.72-0.89]), respectively.

CONCLUSION

In this physiological study involving 30 ICU patients, MAC-DS, end-tidal sevoflurane concentration to get 95% of patients in deep sedation determined over more than 500 observations, is achieved at 0.8% of expired fraction of sevoflurane or at 0.5 age-adjusted MAC.

Breakthrough Medication in Unresponsive Palliative Care Patients: Indications, Practice, and Efficacy

CONTEXT

An unresponsive patient's need and their response to breakthrough medication is determined by clinical assessment and/or observational measures. How closely these methods match the patient's experience is unknown.

OBJECTIVES

Determine the efficacy and effectiveness of breakthrough medication in unresponsive patients and the perception of patient comfort made by nurses and family.

METHODS

A prospective study of breakthrough medication in unresponsive patients. The Richmond Agitation-Sedation Scale (RASS) and Patient Comfort Score (PCS) were compared with time-matched Bispectral Index (BIS) Scores. The effects of opioid vs. opioid + benzodiazepine breakthroughs and the relation between synchronous nurse and family measurements of the PCS were evaluated. Analysis of variance and paired t-tests were used for BIS analyses and nonparametric Mann-Whitney tests for RASS and PCS.

RESULTS

Significant reductions at 30 and 60 minutes after breakthrough medication were noted for BIS (P < 0.0004), RASS (P = 0.043 and 0.004, respectively), and PCS (P < 0.0004). A direct comparison of the effect of opioid breakthrough medication vs. opioid plus benzodiazepine revealed no significant difference (BIS, P = 0.512; RASS, P = 0.195; PCS, P = 0.119). Of the 157 synchronous nurse and family measures of patient comfort, families rated patient discomfort significantly higher than nurses (P < 0.0004).

CONCLUSION

This study provides additional evidence for the efficacy and effectiveness of breakthrough medication and the merit of observational measures in determining a patient's response. The onset of action is evident at 30 minutes after injection. Family assessment of patient comfort may be more nuanced than that of nurses, and they not uncommonly rate patient discomfort higher than nurses.

Monitoring of sedation depth in intensive care unit by therapeutic drug monitoring? A prospective observation study of medical intensive care patients

Background

Analgosedation is a cornerstone therapy for mechanically ventilated patients in intensive care units (ICU). To avoid inadequate sedation and its complications, monitoring of analgosedation is of great importance. The aim of this study was to investigate whether monitoring of analgosedative drug concentrations (midazolam and sufentanil) might be beneficial to optimize analgosedation and whether drug serum concentrations correlate with the results of subjective (Richmond Agitation-Sedation Scale [RASS]/Ramsay Sedation Scale) and objective (bispectral (BIS) index) monitoring procedures.

Methods

Forty-nine intubated, ventilated, and analgosedated critically ill patients treated in ICU were clinically evaluated concerning the depth of sedation using RASS Score, Ramsay Score, and BIS index twice a day. Serum concentrations of midazolam and sufentanil were determined in blood samples drawn at the same time. Clinical and laboratory data were statistically analyzed for correlations using the Spearman’s rank correlation coefficient rho (ρ).

Results

Average age of the population was 57.8 ± 16.0 years, 61% of the patients were males. Most frequent causes for ICU treatments were sepsis (22%), pneumonia (22%), or a combination of both (25%). Serum concentrations of midazolam correlated weakly with RASS (ρ = − 0.467) and Ramsay Scores (ρ = 0.476). Serum concentrations of sufentanil correlated weakly with RASS (ρ = − 0.312) and Ramsay Scores (ρ = 0.295). Correlations between BIS index and serum concentrations of midazolam (ρ = − 0.252) and sufentanil (ρ = − 0.166) were low.

Conclusion

Correlations between drug serum concentrations and clinical or neurophysiological monitoring procedures were weak. This might be due to intersubject variability, polypharmacy with drug-drug interactions, and complex metabolism, which can be altered in critically ill patients. Therapeutic drug monitoring is not beneficial to determine depth of sedation in ICU patients.

Electronic supplementary material

The online version of this article (10.1186/s40560-018-0331-7) contains supplementary material, which is available to authorized users.

BIS monitoring versus clinical assessment for sedation in mechanically ventilated adults in the intensive care unit and its impact on clinical outcomes and resource utilization

BACKGROUND

Patients admitted to intensive care and on mechanical ventilation, are administered sedative and analgesic drugs to improve both their comfort and interaction with the ventilator. Optimizing sedation practice may reduce mortality, improve patient comfort and reduce cost. Current practice is to use scales or scores to assess depth of sedation based on clinical criteria such as consciousness, understanding and response to commands. However these are perceived as subjective assessment tools. Bispectral index (BIS) monitors, which are based on the processing of electroencephalographic signals, may overcome the restraints of the sedation scales and provide a more reliable and consistent guidance for the titration of sedation depth.The benefits of BIS monitoring of patients under general anaesthesia for surgical procedures have already been confirmed by another Cochrane review. By undertaking a well-conducted systematic review our aim was to find out if BIS monitoring improves outcomes in mechanically ventilated adult intensive care unit (ICU) patients.

OBJECTIVES

To assess the effects of BIS monitoring compared with clinical sedation assessment on ICU length of stay (LOS), duration of mechanical ventilation, any cause mortality, risk of ventilator-associated pneumonia (VAP), risk of adverse events (e.g. self-extubation, unplanned disconnection of indwelling catheters), hospital LOS, amount of sedative agents used, cost, longer-term functional outcomes and quality of life as reported by authors for mechanically ventilated adults in the ICU.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, CINAHL, ProQuest, OpenGrey and SciSearch up to May 2017 and checked references citation searching and contacted study authors to identify additional studies. We searched trial registries, which included clinicaltrials.gov and controlled-trials.com.

SELECTION CRITERIA

We included all randomized controlled trials comparing BIS versus clinical assessment (CA) for the management of sedation in mechanically ventilated critically ill adults.

DATA COLLECTION AND ANALYSIS

We used Cochrane's standard methodological procedures. We undertook analysis using Revman 5.3 software.

MAIN RESULTS

We identified 4245 possible studies from the initial search. Of those studies, four studies (256 participants) met the inclusion criteria. One more study is awaiting classification. Studies were, conducted in single-centre surgical and mixed medical-surgical ICUs. BIS monitor was used to assess the level of sedation in the intervention arm in all the studies. In the control arm, the sedation assessment tools for CA included the Sedation-Agitation Scale (SAS), Ramsay Sedation Scale (RSS) or subjective CA utilizing traditional clinical signs (heart rate, blood pressure, conscious level and pupillary size). Only one study was classified as low risk of bias, the other three studies were classified as high risk.There was no evidence of a difference in one study (N = 50) that measured ICU LOS (Median (Interquartile Range IQR) 8 (4 to 14) in the CA group; 12 (6 to 18) in the BIS group; low-quality evidence).There was little or no effect on the duration of mechanical ventilation (MD -0.02 days (95% CI -0.13 to 0.09; 2 studies; N = 155; I² = 0%; low-quality evidence)). Adverse events were reported in one study (N = 105) and the effects on restlessness after suction, endotracheal tube resistance, pain tolerance during sedation or delirium after extubation were uncertain due to very low-quality evidence. Clinically relevant adverse events such as self-extubation were not reported in any study. Three studies reported the amount of sedative agents used. We could not measure combined difference in the amount of sedative agents used because of different sedation protocols and sedative agents used in the studies. GRADE quality of evidence was very low. No study reported other secondary outcomes of interest for the review.

AUTHORS' CONCLUSIONS

We found insufficient evidence about the effects of BIS monitoring for sedation in critically ill mechanically ventilated adults on clinical outcomes or resource utilization. The findings are uncertain due to the low- and very low-quality evidence derived from a limited number of studies.

Bispectral Index Can Reliably Detect Deep Sedation in Mechanically Ventilated Patients: A Prospective Multicenter Validation Study

BACKGROUND

Excessively deep sedation is prevalent in mechanically ventilated patients and often considered suboptimal. We hypothesized that the bispectral index (BIS), a quantified electroencephalogram instrument, would accurately detect deep levels of sedation.

METHODS

We prospectively enrolled 90 critically ill mechanically ventilated patients who were receiving sedation. The BIS was monitored for 24 hours and compared with the Richmond Agitation Sedation Scale (RASS) evaluated every 4 hours. Deep sedation was defined as a RASS of -3 to -5. Threshold values of baseline BIS (the lowest value before RASS assessment) and stimulated BIS (the highest value after standardized assessment) for detecting deep sedation were determined in a training set (45 patients, 262 RASS assessments). Diagnostic accuracy was then analyzed in a validation set (45 patients, 264 RASS assessments).

RESULTS

Deep sedation was only prescribed in 6 (6.7%) patients, but 76 patients (84.4%) had at least 1 episode of deep sedation. Thresholds for detecting deep sedation of 50 for baseline and 80 for stimulated BIS were identified, with respective areas under the receiver-operating characteristic curve of 0.771 (95% confidence interval, 0.714-0.828) and 0.805 (0.752-0.857). The sensitivity and specificity of baseline BIS were 94.0% and 66.5% and of stimulated BIS were 91.0% and 66.5%. When baseline and stimulated BIS were combined, the sensitivity, specificity, and clinical utility index were 85.0% (76.1%-91.1%), 85.9% (79.5%-90.7%), and 66.9% (57.8%-76.0%), respectively.

CONCLUSIONS

Combining baseline and stimulated BIS may help detect deep sedation in mechanically ventilated patients.

Correlation Between Observational Scales of Sedation and Comfort and Bispectral Index Scores

CONTEXT

When palliative care patients enter the phase of unconsciousness preceding death, it is standard practice to initiate or continue a subcutaneous infusion of an opioid plus or minus a sedative. The doses are determined somewhat empirically and adjustments are based on clinical assessment and observational measures of sedation and comfort. Following reports that these observational measures could be misleading, this study assesses their validity by comparing them with an objective measure of sedation, the Bispectral Index Score (BIS).

OBJECTIVE

The objective of this study was to determine the validity of the Richmond Agitation and Sedation Scale (RASS) and the Patient Comfort Score (PCS) in assessing sedation and comfort in unconscious patients.

METHODS

Forty eligible and consenting patients were monitored from the onset of unconsciousness (unresponsiveness) until death. Measures of sedation (RASS) and comfort (PCS) were made by the attending nurse every four hours. Correlation coefficients examined the relationship between fourth hourly RASS and PCS and time-matched BISs.

RESULTS

A significant correlation was found between RASS and BIS and PCS and BIS. Sedation and comfort scores were concentrated at the lower end of the respective scales, whereas time-matched BISs were widely scattered with scores ranging from near full awareness to deep sedation.

CONCLUSIONS

Compared with BIS, both RASS and PCS appear to be relatively blunt instruments at the lower end of their respective scales. Due caution should be taken interpreting and making clinical decisions based solely on the RASS and PCS and, by extension, other observational measures of patient comfort and sedation.

Neurophysiological assessment of brain dysfunction in critically ill patients: an update

The aim of this review was to provide up-to-date information about the usefulness of clinical neurophysiology testing in the management of critically ill patients. Evoked potentials (EPs) and electroencephalogram (EEG) are non-invasive clinical neurophysiology tools that allow an objective assessment of the central nervous system's function at the bedside in intensive care unit (ICU). These tests are quite useful in diagnosing cerebral complications, and establishing the vital and functional prognosis in ICU. EEG keeps a particularly privileged importance in detecting seizures phenomena such as subclinical seizures and non-convulsive status epilepticus. Quantitative EEG (QEEG) analysis techniques commonly called EEG Brain mapping can provide obvious topographic displays of digital EEG signals characteristics, showing the potential distribution over the entire scalp including filtering, frequency, and amplitude analysis and color mapping. Evidences of usefulness of QEEG for seizures detection in ICU are provided by several recent studies. Furthermore, beyond detection of epileptic phenomena, changes of some QEEG panels are early warning indicators of sedation level as well as brain damage or dysfunction in ICU. EPs offer the opportunity for assessing brainstem's functional integrity, as well as subcortical and cortical brain areas. A multimodal use, combining EEG and various modalities of EPs is recommended since this allows a more accurate functional exploration of the brain and helps caregivers to tailor therapeutic measures according to neurological worsening trends and to anticipate the prognosis in ICU.

Evidence and consensus based guideline for the management of delirium, analgesia, and sedation in intensive care medicine. Revision 2015 (DAS-Guideline 2015) - short version

In 2010, under the guidance of the DGAI (German Society of Anaesthesiology and Intensive Care Medicine) and DIVI (German Interdisciplinary Association for Intensive Care and Emergency Medicine), twelve German medical societies published the “Evidence- and Consensus-based Guidelines on the Management of Analgesia, Sedation and Delirium in Intensive Care”. Since then, several new studies and publications have considerably increased the body of evidence, including the new recommendations from the American College of Critical Care Medicine (ACCM) in conjunction with Society of Critical Care Medicine (SCCM) and American Society of Health-System Pharmacists (ASHP) from 2013. For this update, a major restructuring and extension of the guidelines were needed in order to cover new aspects of treatment, such as sleep and anxiety management. The literature was systematically searched and evaluated using the criteria of the Oxford Center of Evidence Based Medicine. The body of evidence used to formulate these recommendations was reviewed and approved by representatives of 17 national societies. Three grades of recommendation were used as follows: Grade “A” (strong recommendation), Grade “B” (recommendation) and Grade “0” (open recommendation). The result is a comprehensive, interdisciplinary, evidence and consensus-based set of level 3 guidelines. This publication was designed for all ICU professionals, and takes into account all critically ill patient populations. It represents a guide to symptom-oriented prevention, diagnosis, and treatment of delirium, anxiety, stress, and protocol-based analgesia, sedation, and sleep-management in intensive care medicine.

A randomized controlled proof-of-concept trial of early sedation management using Responsiveness Index monitoring in mechanically ventilated critically ill patients

INTRODUCTION

Deep sedation is associated with adverse patient outcomes. We recently described a novel sedation-monitoring technology, the Responsiveness Index (RI), which quantifies patient arousal using processed frontal facial EMG data. We explored the potential effectiveness and safety of continuous RI monitoring during early intensive care unit (ICU) care as a nurse decision-support tool.

METHODS

In a parallel-group controlled single centre proof of concept trial, patients requiring mechanical ventilation and sedation were randomized via sequential sealed envelopes following ICU admission. Control group patients received hourly clinical sedation assessment and daily sedation holds; the RI monitor was connected but data were concealed from clinical staff. The intervention group received control group care, but RI monitoring was visible and nurses were asked to adjust sedation to maintain patients with an RI>20 whenever possible. Traffic-light colour coding (RI<20, Red; 20-40, Amber; >40, Green) simplified decision-making. The intervention lasted up to 48 hours. Sixteen nurses were interviewed to explore their views of the novel technology.

RESULTS

We analysed 74 patients treated per protocol (36 intervention; 38 control). The proportion of patients with RI<20 was identical at the start of monitoring (54% both groups). Overall, the proportion of time with RI<20 trended to lower values for the intervention group (median 16% (1-3rd quartile 8-30%) versus 33% (10-54%); P = 0.08); sedation and analgesic use was similar. A post hoc analysis restricted to patients with RI<20 when monitoring started, found intervention patients spent less time with low RI value (16% (11-45%) versus 51% (33-72%); P = 0.02), cumulative propofol use trended to lower values (median 1090 mg versus 2390 mg; P = 0.14), and cumulative alfentanil use was lower (21.2 mg versus 32.3 mg; P = 0.01). RASS scores were similar for both groups. Sedation related adverse event rates were similar (7/36 versus 5/38). Similar proportions of patients had sedation holds (83% versus 87 %) and were extubated (47% versus 44%) during the intervention period. Nurses valued the objective visible data trends and simple colour prompts, and found RI monitoring a useful adjunct to existing practice.

CONCLUSIONS

RI monitoring was safe and acceptable. Data suggested potential to modify sedation decision-making. Larger trials are justified to explore effects on patient-centred outcomes.

TRIAL REGISTRATION

NCT01361230 (registered April 19, 2010).

Utility of bispectral index in the management of multiple trauma patients

Background:

Bispectral index (BIS) monitoring in multiple trauma patients has become a common practice in monitoring the sedation levels. We aimed to assess the utility of BIS in the trauma intensive care unit (ICU).

Methods:

A prospective observational study was conducted in the trauma ICU at Hamad General Hospital in Qatar between 2011 and 2012. Patients were divided in two groups: Group I (without BIS monitoring) and Group II (with BIS monitoring). The depth of sedation was clinically evaluated with Ramsey Sedation Scale, changes in vital signs and Glasgow Coma Scale (GCS) level. Use of sedatives, analgesics, and muscle relaxants were also recorded. Data were compared using Chi-square and Student t-tests.

Results:

A total of 110 mechanically ventilated trauma patients were enrolled with a mean age of 36 ± 14 years. The rate of head injury was greater in Group I when compared with Group II (94% vs. 81%, P = 0.04). In comparison to Group I, patients in Group II had lower GCS and higher mean Injury Severity Score (ISS) (6.3 ± 2.5 vs. 7.4 ± 2.7 and 25.5 ± 8.5 vs. 21.2 ± 4.7, respectively, P = 0.03). The used midazolam dose was less in Group II in comparison to Group I (5.2 ± 2.3 vs. 6.1 ± 2.1, P = 0.03). Also, fentanyl dose was less in Group II (152 ± 58 vs. 187 ± 59, P = 0.004). The rate of agitation, failure of extubation and tracheostomy in Group II were lower than those in Group I, P = 0.001. The length of stay for patients Group I was longer (14.6 ± 7.1 vs. 10.2 ± 5.9 days) in comparison to group II, P = 0.001.

Conclusion:

Management of multiple trauma patients in the trauma ICU with BIS monitoring was found to be associated with better outcomes. BIS monitoring is a guide for adjusting the dosage of sedative agents. It can also minimize agitation, failure of extubation, and length of stay in ICU.

The use of the bispectral index in the detection of pain in mechanically ventilated adults in the intensive care unit: a review of the literature

The bispectral index is a technique that involves assessing brain activity (through electroencephalography as well as electromyography), and has been proposed to be useful for the detection of pain among patients who are unable to communicate verbally. This review aimed to clarify whether the bispectral index is an appropriate tool to assess pain in the intensive care unit.

BACKGROUND:

Pain assessment is an immense challenge for clinicians, especially in the context of the intensive care unit, where the patient is often unable to communicate verbally. Several methods of pain assessment have been proposed to assess pain in this environment. These include both behavioural observation scales and evaluation of physiological measurements such as heart rate and blood pressure. Although numerous validation studies pertaining to behavioural observation scales have been published, several limitations associated with using these measures for pain assessment remain. Over the past few years, researchers have been interested in the use of the bispectral index monitoring system as a proxy for the evaluation of encephalography readings to assess the level of anesthesia and, potentially, analgesia.

OBJECTIVES:

To synthesize the main studies exploring the use of the bispectral index monitoring system for pain assessment, to guide future research in adults under sedation in the intensive care unit.

METHOD:

The EMBASE, Medline, CINAHL and PsycINFO databases were searched for studies published between 1996 and 2013 that evaluated the use of the bispectral index in assessing pain.

RESULTS:

Most studies conclude that nociceptive stimulation causes a significant increase in the bispectral index and revealed the importance of controlling certain confounding variables such as the level of sedation.

DISCUSSION:

Further studies are needed to clearly demonstrate the relationship between nociceptive stimuli and the bispectral index, as well as the specificity of the bispectral index in detecting pain.

Sleep disturbance in older ICU patients

Maintaining a stable and adequate sleeping pattern is associated with good health and disease prevention. As a restorative process, sleep is important for supporting immune function and aiding the body in healing and recovery. Aging is associated with characteristic changes to sleep quantity and quality, which make it more difficult to adjust sleep–wake rhythms to changing environmental conditions. Sleep disturbance and abnormal sleep–wake cycles are commonly reported in seriously ill older patients in the intensive care unit (ICU). A combination of intrinsic and extrinsic factors appears to contribute to these disruptions. Little is known regarding the effect that sleep disturbance has on health status in the oldest of old (80+), a group, who with diminishing physiological reserve and increasing prevalence of frailty, is at a greater risk of adverse health outcomes, such as cognitive decline and mortality. Here we review how sleep is altered in the ICU, with particular attention to older patients, especially those aged ≥80 years. Further work is required to understand what impact sleep disturbance has on frailty levels and poor outcomes in older critically ill patients.

An evaluation of the validity and potential utility of facial electromyelogram Responsiveness Index for sedation monitoring in critically ill patients

PURPOSE

The purpose of this study is to explore the validity of a novel sedation monitoring technology based on facial electromyelography (EMG) in sedated critically ill patients.

MATERIALS AND METHODS

The Responsiveness Index (RI) integrates the preceding 60 minutes of facial EMG data. An existing data set was used to derive traffic light cut-offs for low (red), intermediate (amber), and higher (green) states of patient arousal. The validity of these was prospectively evaluated in 30 sedated critically ill patients against hourly Richmond Agitation Sedation Scale (RASS) assessments with concealment of RI data from clinical staff.

RESULTS

With derivation data, an RI less than or equal to 35 had best discrimination for a Ramsay score of 5/6 (sensitivity, 90%; specificity, 79%). For traffic lights, we chose RI less than or equal to 20 as red, 20 to 40 as amber, and more than 40 as green. In the prospective study, RI values were red/amber for 76% of RASS -5/-4 assessments, but RI varied dynamically over time in many patients, and discordance with RASS may have resulted from the use of 1 hour of data for RI calculations. We also noted that red/amber values resulted from sleep, encephalopathy, and low levels of stimulation.

CONCLUSIONS

Responsiveness Index is not directly comparable with clinical sedation scores but is a potential continuous alert to possible deep sedation in critically ill patients.

Sedation in neurological intensive care unit

Analgesia and sedation has been widely used in intensive care units where iatrogenic discomfort often complicates patient management. In neurological patients maximal comfort without diminishing patient responsiveness is desirable. In these patients successful management of sedation and analgesia incorporates a patient based approach that includes detection and management of predisposing and causative factors, including delirium, monitoring using sedation scales, proper medication selection, emphasis on analgesia based drugs and incorporation of protocols or algorithms. So, to optimize care clinician should be familiar with the pharmacokinetic and pharmacodynamic variables that can affect the safety and efficacy of analgesics and sedatives.

Prognostic evaluation of bispectral index in patients following cardiopulmonary resuscitation

The aim of this study was to evaluate the prognosis of patients following cardiopulmonary resuscitation in an intensive care unit (ICU) using bispectral index (BIS) monitoring. The study was a prospective comparative study performed at the academic department of an ICU. A total of 33 adults who received cardiopulmonary resuscitation were enrolled and divided into the surviving and non-surviving groups according to their 7-day survival status. During their stay in the ICU, the BIS and arterial oxygen saturation (SaO₂) levels of all the patients were continuously monitored. The neurological condition of the patients was measured according to the Glasgow coma scale (GCS). Acute physiological and chronic diseases were measured according to the acute physiology and chronic health evaluation II (APACHE II). SaO₂ was monitored in all patients. The jugular bulb venous oxygen saturation (SjO₂) levels were continuously monitored in 23 patients and the difference between the SaO₂ and SjO₂ values was used to indicate oxygen metabolism in the brain. The variables in the present study were compared between the 2 groups. The correlations between BIS values and GCS or APACHE II scores were analyzed. The BIS values were significantly higher in the surviving group than in the non-surviving group (P<0.01). The difference between the SaO₂ and SjO₂ was significant (P<0.01). There was a positive correlation between BIS values and GCS scores (r=0.821, P<0.01) and between BIS values and APACHE II scores (r=0.434, P<0.05). BIS values may be used to predict the post-resuscitative outcome of patients following cardiopulmonary resuscitation.

The use of observational scales to monitor symptom control and depth of sedation in patients requiring palliative sedation: a systematic review

BACKGROUND

Palliative sedation is the intentional lowering of consciousness of a patient in the last phase of life to relieve suffering from refractory symptoms such as pain, delirium and dyspnoea.

AIM

In this systematic review, we evaluated the use of monitoring scales to assess the degree of control of refractory symptoms and/or the depth of the sedation.

DESIGN

A database search of PubMed and Embase was performed up to January 2010 using the search terms 'palliative sedation' OR 'terminal sedation'.

DATA SOURCES

Retro- and prospective studies as well as reviews and guidelines containing information about monitoring of palliative sedation, written in the English, German or Dutch language were included.

RESULTS

The search yielded 264 articles of which 30 were considered relevant. Most studies focused on monitoring refractory symptoms (pain, fatigue or delirium) or the level of awareness to control the level of sedation. Four prospective and one retrospective study used scales validated in other settings: the Numeric Pain Rating Scale, the Visual Analogue Scale, the Memorial Delirium Assessment Scale, the Communication Capacity Scale and Agitation Distress Scale. Only the Community Capacity Scale was partially validated for use in a palliative sedation setting. One guideline described the use of a scale validated in another setting.

CONCLUSIONS

A minority of studies reported the use of observational scales to monitor the effect of palliative sedation. Future studies should be focused on establishing proper instruments, most adequate frequency and timing of assessment, and interdisciplinary evaluation of sedation depth and symptom control for palliative sedation.

Sedation for critically ill or injured adults in the intensive care unit: a shifting paradigm

As most critically ill or injured patients will require some degree of sedation, the goal of this paper was to comprehensively review the literature associated with use of sedative agents in the intensive care unit (ICU). The first and selected latter portions of this article present a narrative overview of the shifting paradigm in ICU sedation practices, indications for uninterrupted or prolonged ICU sedation, and the pharmacology of sedative agents. In the second portion, we conducted a structured, although not entirely systematic, review of the available evidence associated with use of alternative sedative agents in critically ill or injured adults. Data sources for this review were derived by searching OVID MEDLINE and PubMed from their first available date until May 2012 for relevant randomized controlled trials (RCTs), systematic reviews and/or meta-analyses and economic evaluations. Advances in the technology of mechanical ventilation have permitted clinicians to limit the use of sedation among the critically ill through daily sedative interruptions or other means. These practices have been reported to result in improved mortality, a decreased length of ICU and hospital stay and a lower risk of drug-associated delirium. However, in some cases, prolonged or uninterrupted sedation may still be indicated, such as when patients develop intracranial hypertension following traumatic brain injury. The pharmacokinetics of sedative agents have clinical importance and may be altered by critical illness or injury, co-morbid conditions and/or drug-drug interactions. Although use of validated sedation scales to monitor depth of sedation is likely to reduce adverse events, they have no utility for patients receiving neuromuscular receptor blocking agents. Depth of sedation monitoring devices such as the Bispectral Index (BIS©) also have limitations. Among existing RCTs, no sedative agent has been reported to improve the risk of mortality among the critically ill or injured. Moreover, although propofol may be associated with a shorter time to tracheal extubation and recovery from sedation than midazolam, the risk of hypertriglyceridaemia and hypotension is higher with propofol. Despite dexmedetomidine being linked with a lower risk of drug-associated delirium than alternative sedative agents, this drug increases risk of bradycardia and hypotension. Among adults with severe traumatic brain injury, there are insufficient data to suggest that any single sedative agent decreases the risk of subsequent poor neurological outcomes or mortality. The lack of examination of confounders, including the type of healthcare system in which the investigation was conducted, is a major limitation of existing pharmacoeconomic analyses, which likely limits generalizability of their results.

Increased sedation requirements in patients receiving extracorporeal membrane oxygenation for respiratory and cardiorespiratory failure

Critically ill patients receiving extracorporeal membrane oxygenation (ECMO) are often noted to have increased sedation requirements. However, data related to sedation in this complex group of patients is limited. The aim of our study was to characterise the sedation requirements in adult patients receiving ECMO for cardiorespiratory failure. A retrospective chart review was performed to collect sedation data for 30 consecutive patients who received venovenous or venoarterial ECMO between April 2009 and March 2011. To test for a difference in doses over time we used a regression model. The dose of midazolam received on ECMO support increased by an average of 18 mg per day (95% confidence interval 8, 29 mg, P=0.001), while the dose of morphine increased by 29 mg per day (95% confidence interval 4, 53 mg, P=0.021) The venovenous group received a daily midazolam dose that was 157 mg higher than the venoarterial group (95% confidence interval 53, 261 mg, P=0.005). We did not observe any significant increase in fentanyl doses over time (95% confidence interval 1269, 4337 µg, P=0.94). There is a significant increase in dose requirement for morphine and midazolam during ECMO. Patients on venovenous ECMO received higher sedative doses as compared to patients on venoarterial ECMO. Future research should focus on mechanisms behind these changes and also identify drugs that are most suitable for sedation during ECMO.

Influence of progressive hemorrhage and subsequent cardiopulmonary resuscitation on the bispectral index during isoflurane anesthesia in a swine model

BACKGROUND

The bispectral index for measurement of anesthetic depth may be modified by extreme hypotension during hemorrhagic shock. In this study, the influence of progressive hemorrhage and subsequent cardiopulmonary resuscitation on the bispectral index was investigated under controlled anesthetic depth.

METHODS

Fifteen swine were anesthetized through inhalation of isoflurane under bispectral index monitoring. Hemorrhagic shock was induced using a stepwise hemorrhage model in which 20%, 10%, and 10% of estimated blood volume were removed over three 30-minute periods and then 5% was removed every 30 minutes until the mean arterial pressure was less than 10 mm Hg. After reaching this criterion, chest compression with 0.2-mg/kg epinephrine and hydroxyethyl starch infusion was performed for 20 minutes or until the mean arterial pressure exceeded 50 mm Hg. The pharmacodynamics of the isoflurane effect was examined before hemorrhage, after 40% bleeding, and after resuscitation.

RESULTS

A mean (SD) volume of 836 (78) mL of blood was drained before resuscitation. The bispectral index suddenly decreased at a mean (SD) arterial pressure of 22 (3) mm Hg and showed isoelectric activity in most animals before resuscitation. Eight pigs were resuscitated, and the bispectral index recovered during a range of periods after recovery of the mean arterial pressure. The pharmacodynamic effect of isoflurane did not change after 40% bleeding but increased after resuscitation, with the alteration correlated with the time for resuscitation.

CONCLUSION

In hemorrhagic shock, the bispectral index merely reflects the anesthetic depth until development of lethal hypotension at which brain electrical activity cannot be sustained. After recovery from depression, the potency of isoflurane can increase depending on the cerebral hypoperfusion time. The increased bispectral index for anesthetics after resuscitation might reflect the degree of cerebral damage due to hypoperfusion.

The utility of bispectral index monitoring for sedated patients treated with low-dose remifentanil

The aim of the present study was to determine the effect of low-dose remifentanil on the monitoring quality of the Bispectral index for mechanically ventilated patients. Twelve patients who underwent elective surgery and required mechanical ventilation post-operatively were enrolled in this study with written informed consent. Eligible patients were divided into two groups. Patients in the remifentanil group received low-dose remifentanil (0.05-0.125 μg/kg/min) and propofol (1-3 mg/kg/h). Patients in the control group received propofol (1-3 mg/kg/h). Levels of sedation were evaluated by both the Richmond Agitation Sedation Scale (RASS) and BIS monitor (A2000-XP, version 4.0, Aspect Medical Systems, Newton, USA). Monitoring quality was assessed by a correlation between RASS and BIS values. These values were assessed by single regression analysis and a P value of <0.05 was considered significant. There was a significant correlation between RASS and BIS values (P = 3 × 10(-12), R (2) = 0.67) in the remifentanil group, but not in the control group (P = 0.50, R (2) = 0.057). The administration of low-dose remifentanil makes BIS a more precise tool for sedated patients under mechanical ventilation in the ICU.

Electroencephalogram-based pharmacodynamic measures: a review

Pharmacokinetics and pharmacodynamics can provide a useful modeling framework for predicting drug activity and can serve as a basis for dose optimization. Determining a suitable biomarker or surrogate measure of drug effect for pharmacodynamic models can be challenging. The electroencephalograph is a widely-available and non-invasive tool for recording brainwave activity simultaneously from multiple brain regions. Certain drug classes (such as drugs that act on the central nervous system) also generate a reproducible electroencephalogram (EEG) effect. Characterization of such a drug-induced EEG effect can produce pharmacokinetic/pharmacodynamic models useful for titrating drug levels and expediting development of chemically-similar drug analogs. This paper reviews the relevant concepts involved in pharmacokinetic/pharmacodynamic modeling using EEG-based pharmacodynamic measures. In addition, examples of such models for various drugs are organized by drug activity as well as chemical structure and presented.

Spectral entropy for assessing the depth of propofol sedation

Background

For patients in the intensive care unit (ICU) or under monitored anesthetic care (MAC), the precise monitoring of sedation depth facilitates the optimization of dosage and prevents adverse complications from underor over-sedation. For this purpose, conventional subjective sedation scales, such as the Observer's Assessment of Alertness/Sedation (OAA/S) or the Ramsay scale, have been widely utilized. Current procedures frequently disturb the patient's comfort and compromise the already well-established sedation. Therefore, reliable objective sedation scales that do not cause disturbances would be beneficial. We aimed to determine whether spectral entropy can be used as a sedation monitor as well as determine its ability to discriminate all levels of propofol-induced sedation during gradual increments of propofol dosage.

Methods

In 25 healthy volunteers undergoing general anesthesia, the values of response entropy (RE) and state entropy (SE) corresponding to each OAA/S (5 to 1) were determined. The scores were then analyzed during each 0.5 mcg/ml- incremental increase of a propofol dose.

Results

We observed a reduction of both RE and SE values that correlated with the OAA/S (correlation coefficient of 0.819 in RE-OAA/S and 0.753 in SE-OAA/S). The RE and SE values corresponding to awake (OAA/S score 5), light sedation (OAA/S 3-4) and deep sedation (OAA/S 1-2) displayed differences (P < 0.05).

Conclusions

The results indicate that spectral entropy can be utilized as a reliable objective monitor to determine the depth of propofol-induced sedation.

Sleep deprivation in critical illness: its role in physical and psychological recovery

Critically ill patients frequently experience poor sleep, characterized by frequent disruptions, loss of circadian rhythms, and a paucity of time spent in restorative sleep stages. Factors that are associated with sleep disruption in the intensive care unit (ICU) include patient-ventilator dysynchrony, medications, patient care interactions, and environmental noise and light. As the field of critical care increasingly focuses on patients' physical and psychological outcomes following critical illness, understanding the potential contribution of ICU-related sleep disruption on patient recovery is an important area of investigation. This review article summarizes the literature regarding sleep architecture and measurement in the critically ill, causes of ICU sleep fragmentation, and potential implications of ICU-related sleep disruption on patients' recovery from critical illness. With this background information, strategies to optimize sleep in the ICU are also discussed.

Bispectral index to monitor propofol sedation in trauma patients

BACKGROUND

This study tested the hypothesis that the bispectral index (BIS) is reliable relative to clinical judgment for estimating sedation level during daily propofol spontaneous awakening trials (SATs) in trauma patients.

METHODS

This was a prospective observational trial with waiver of consent conducted in the intensive care unit of Level I trauma center in 94 mechanically ventilated trauma patients sedated with propofol alone or in combination with midazolam. BIS, Richmond Agitation Sedation Scale (RASS), electromyography, and heart rate variability, as a test of autonomic function, were measured for 45 minutes during daily SATs. Data were evaluated with analysis of variance, linear regression, and nonparametric tests.

RESULTS

The BIS wave form coincided almost exactly with propofol on/off. Steady-state BIS correlated with RASS (p < 0.0001) and with propofol dose (p < 0.0001), but the strengths of association were relatively low (all r(2) < 0.5). BIS wave form was not altered by age, heart rate, or heart rate variability and was similar with propofol alone or propofol plus midazolam, but the presence of brain injury or the use of paralytics shifted the curve downward (both p < 0.001). The overall test characteristics for BIS versus RASS without neuromuscular blockade were sensitivity: 90% versus 77% (p = 0.034); specificity: 90% versus 75% (p = 0.021); positive predictive value: 90% versus 76% (p = 0.021), and negative predictive value: 90% versus 76% (p = 0.021).

CONCLUSIONS

In the first trial in trauma patients and largest trial in any surgical population, the (1) BIS was reliable and has advantages over RASS of being continuous and objective, at least during a propofol SAT; (2) BIS interpretation remains somewhat subjective in patients receiving paralytic agents or with traumatic brain injury.

Pharmacoeconomics of sedation in the ICU

Despite considerable information on the pharmacotherapy of sedation in the ICU, there is little published on the pharmacoeconomics of sedation in patients who are critically ill. The purpose of this article is to discuss the various components that contribute to the cost of treating the agitated ICU patient and to critically review the articles published since 2000 that evaluated costs and cost-effectiveness in ICU patients receiving drugs for agitation and/or pain. Clinicians should look beyond the acquisition cost of a sedative and include the effect of sedatives on the cost of care when selecting the most appropriate sedative.

Sedation and analgesia in the mechanically ventilated patient

Sedation and analgesia are important components of care for the mechanically ventilated patient in the intensive care unit (ICU). An understanding of commonly used medications is essential to formulate a sedation plan for individual patients. The specific physiological changes that a critically ill patient undergoes can have direct effects on the pharmacology of drugs, potentially leading to interpatient differences in response. Objective assessments of pain, sedation, and agitation have been validated for use in the ICU for assessment and titration of medications. An evidence-based strategy for administering these drugs can lead to improvements in short- and long-term outcomes for patients. In this article, we review advances in the field of ICU sedation to provide an up-to-date perspective on management of the mechanically ventilated ICU patient.

Analytic reviews: managing the agitated patient in the ICU: sedation, analgesia, and neuromuscular blockade

Physical and psychological distress is exceedingly common among critically ill patients and manifests generically as agitation. The dangers of over- and undertreatment of agitation have been well described, and the intensive care unit (ICU) physician must strike a balance in the fast-paced, dynamic ICU environment. Identification of common reversible etiologies for distress may obviate the need for pharmacologic therapy, but most patients receive some combination of sedative, analgesic, and neuroleptic medications during the course of their critical illness. As such, understanding key pharmacologic features of commonly used agents is critical. Structured protocols and objective assessment tools can optimize drug delivery and may ultimately improve patient outcomes by reducing ventilator days, ICU length of stay, and by reducing cognitive dysfunction.

[Sedation and analgesia in intensive care: physiology and application]

Many therapeutic and diagnostic procedures in intensive care medicine are perceived as painful by most patients. As a consequence analgesia and sedation represent two of the main pillars in the treatment of the critically ill. Adaptation to the individual needs of the patients poses one of the biggest challenges that we are confronted with. Both morbidity and mortality can be positively influenced by adequate treatment. In the first part of this review we will discuss the physiology of sleep patterns and pain. Furthermore modes of action and side effects of the most common anesthetics and analgetics will be presented. Finally, the last part of the manuscript deals with the practical application of these therapeutics and their monitoring in intensive care medicine.

A comparison of SNAP II and bispectral index monitoring in patients undergoing sedation

Clinical signs and patients' verbal responses have traditionally been used to assess patients' comfort and the depth of sedation. Recently, level-of-consciousness monitors have been used to guide sedation. The SNAP II(c) is a single-lead electroencephalogram device that displays a SNAP(c) Index - a derived value based on both high and low frequency electroencephalogram signals. Much of the current clinical research on monitoring during sedation involves the bispectral index monitor. We compared simultaneous readings recorded by the SNAP II and bispectral index during sedation in 51 consecutive patients undergoing surgery. The anaesthesia team was blinded to the SNAP II and bispectal index values. Concurrent SNAP II and bispectral index readings displayed similarly-shaped trajectories during sedation, but further studies are needed to establish the routine clinical utility of both these monitors.

Evidence and consensus-based German guidelines for the management of analgesia, sedation and delirium in intensive care--short version

Targeted monitoring of analgesia, sedation and delirium, as well as their appropriate management in critically ill patients is a standard of care in intensive care medicine. With the undisputed advantages of goal-oriented therapy established, there was a need to develop our own guidelines on analgesia and sedation in intensive care in Germany and these were published as 2(nd) Generation Guidelines in 2005. Through the dissemination of these guidelines in 2006, use of monitoring was shown to have improved from 8 to 51% and the use of protocol-based approaches increased to 46% (from 21%). Between 2006-2009, the existing guidelines from the DGAI (Deutsche Gesellschaft für Anästhesiologie und Intensivmedizin) and DIVI (Deutsche Interdisziplinäre Vereinigung für Intensiv- und Notfallmedizin) were developed into 3(rd) Generation Guidelines for the securing and optimization of quality of analgesia, sedation and delirium management in the intensive care unit (ICU). In collaboration with another 10 professional societies, the literature has been reviewed using the criteria of the Oxford Center of Evidence Based Medicine. Using data from 671 reference works, text, diagrams and recommendations were drawn up. In the recommendations, Grade "A" (very strong recommendation), Grade "B" (strong recommendation) and Grade "0" (open recommendation) were agreed. As a result of this process we now have an interdisciplinary and consensus-based set of 3(rd) Generation Guidelines that take into account all critically illness patient populations. The use of protocols for analgesia, sedation and treatment of delirium are repeatedly demonstrated. These guidelines offer treatment recommendations for the ICU team. The implementation of scores and protocols into routine ICU practice is necessary for their success.

Continuous EEG monitoring: is it ready for prime time?

PURPOSE OF REVIEW

Continuous electroencephalography (cEEG) is being used more frequently in intensive care units to detect epileptic activity and ischemia. This review analyzes clinical applications and limitations of cEEG as a routine neuromonitoring tool.

RECENT FINDINGS

cEEG is primarily used to detect nonconvulsive seizures, which are frequent and possibly associated with harm. Cerebral ischemia, such as that from vasospasm after subarachnoid hemorrhage, can be detected earlier by EEG and quantitative EEG (qEEG). Highly skilled technicians and subspecialty-trained physicians are needed to generate good quality EEG and to interpret these data. qEEG allows more efficient interpretation of large amounts of EEG and may trigger prespecified alarms. Currently, there is little high-quality data on cEEG to define indications, cost-saving potential, and impact on outcome. A few studies have demonstrated how cEEG can be integrated into multimodality brain monitoring of severely brain-injured patients.

SUMMARY

cEEG should be considered as an integral part of multimodality monitoring of the injured brain, particularly in patients at risk for nonconvulsive seizure or ischemia. Automated alarms may help establish cEEG monitoring as an integral part of brain monitoring. All neurological ICUs that routinely care for patients with refractory status epilepticus should have the capability to perform cEEG monitoring. Further research determining the impact on outcome and making EEG monitoring more user friendly may help move this technique out of the subspecialized ICU setting into the general ICU environment. In the future, it may be possible to use specific EEG parameters as endpoints for therapeutic interventions.

Pharmacoeconomics of sedation in the ICU

Despite considerable information on the pharmacotherapy of sedation in the ICU, there is little published on the pharmacoeconomics of sedation in patients who are critically ill. The purpose of this article is to discuss the various components that contribute to the cost of treating the agitated ICU patient and to critically review the articles published since 2000 that evaluated costs and cost-effectiveness in ICU patients receiving drugs for agitation and/or pain. Clinicians should look beyond the acquisition cost of a sedative and include the effect of sedatives on the cost of care when selecting the most appropriate sedative.

Auditory event-related potentials, bispectral index, and entropy for the discrimination of different levels of sedation in intensive care unit patients

BACKGROUND

Sedation protocols, including the use of sedation scales and regular sedation stops, help to reduce the length of mechanical ventilation and intensive care unit stay. Because clinical assessment of depth of sedation is labor-intensive, performed only intermittently, and interferes with sedation and sleep, processed electrophysiological signals from the brain have gained interest as surrogates. We hypothesized that auditory event-related potentials (ERPs), Bispectral Index (BIS), and Entropy can discriminate among clinically relevant sedation levels.

METHODS

We studied 10 patients after elective thoracic or abdominal surgery with general anesthesia. Electroencephalogram, BIS, state entropy (SE), response entropy (RE), and ERPs were recorded immediately after surgery in the intensive care unit at Richmond Agitation-Sedation Scale (RASS) scores of -5 (very deep sedation), -4 (deep sedation), -3 to -1 (moderate sedation), and 0 (awake) during decreasing target-controlled sedation with propofol and remifentanil. Reference measurements for baseline levels were performed before or several days after the operation.

RESULTS

At baseline, RASS -5, RASS -4, RASS -3 to -1, and RASS 0, BIS was 94 [4] (median, IQR), 47 [15], 68 [9], 75 [10], and 88 [6]; SE was 87 [3], 46 [10], 60 [22], 74 [21], and 87 [5]; and RE was 97 [4], 48 [9], 71 [25], 81 [18], and 96 [3], respectively (all P < 0.05, Friedman Test). Both BIS and Entropy had high variabilities. When ERP N100 amplitudes were considered alone, ERPs did not differ significantly among sedation levels. Nevertheless, discriminant ERP analysis including two parameters of principal component analysis revealed a prediction probability PK value of 0.89 for differentiating deep sedation, moderate sedation, and awake state. The corresponding PK for RE, SE, and BIS was 0.88, 0.89, and 0.85, respectively.

CONCLUSIONS

Neither ERPs nor BIS or Entropy can replace clinical sedation assessment with standard scoring systems. Discrimination among very deep, deep to moderate, and no sedation after general anesthesia can be provided by ERPs and processed electroencephalograms, with similar P(K)s. The high inter- and intraindividual variability of Entropy and BIS precludes defining a target range of values to predict the sedation level in critically ill patients using these parameters. The variability of ERPs is unknown.