Comparing BIS monitoring with clinical assessment for determining the level of sedation of mechanically ventilated adults in intensive care units

Review question

We reviewed the evidence for benefits of bispectral index (BIS) monitoring compared to clinical assessment (CA) methods in adults connected to a breathing machine (ventilator) in the intensive care unit (ICU).


BIS monitoring follows brain electrical activity to produce scores. These scores may help hospital staff decide whether a person in ICU who is on a ventilator is receiving enough sedative to make them comfortable and accept the ventilator. Sedatives are drugs taken for their calming and sleep-inducing effects. Giving of too much, or too little, sedative could lead to harm. In the CA method, observing clinical factors such as consciousness, understanding and response to commands helps to assess the depth of sedation or sleep. The score provided by the BIS monitor is not dependent on a person. Monitoring by CA might vary between caregivers.

Our aim was to find out if BIS monitoring is beneficial compared to CA for critically ill adults on a ventilator.

Study characteristics

The evidence identified from our literature search is current to May 2017. Four randomized controlled studies met the inclusion criteria for this review (involving 256 adults). One more study is awaiting classification. These studies were conducted in adult surgical and mixed medical-surgical ICUs, and compared BIS monitoring with various measures for CA.

Study funding sources

For one study, the BIS monitoring devices manufacturer provided equipment. The company had no role in the conduct of the study. Another study was funded as part of a scientific and technological project. No funding information was available for the other two studies.

Key results

With BIS monitoring, we found no significant differences in ICU length of stay (one study, 50 adults), duration of ventilation (two studies, 155 adults) and the risk of adverse events (one study, 105 adults) compared with CA. Clinically relevant adverse events, for example, accidental self-removal of the breathing tube, were not reported. We could not measure combined difference in amount of sedative use because of the different sedation protocols and sedatives used. None of the other outcomes of interest for the review, for example, death, ventilator-associated pneumonia, quality of life etc. were reported in any of the studies.

Quality of evidence

The findings of our review are from a limited number of studies which provided 'low to very low' GRADE quality of evidence.


The authors of this review conclude that we found insufficient evidence about the effects of BIS monitoring compared with CA of sedation in critically ill adults who were on a ventilator.

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.

Read the full abstract...

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.


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 strategy: 

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 and

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.