Correlation between the Sedation-Agitation Scale and the Bispectral Index in ventilated patients in the intensive care unit

Background

Oversedation masks neurologic changes and increases mortality/morbidity, whereas undersedation risks prolonged stress mobilization and patient injury. In situations such as deep sedation/analgesia, the Bispectral Index (BIS) has potential use as an adjunct to clinical assessment of sedation to help determine depth of sedation. Determining the correlation between clinical and BIS measures of sedation will help to determine the correct role of BIS in intensive care unit (ICU) practice settings.

Objective

To evaluate the correlation between the clinical assessment of sedation using the Sedation-Agitation Scale (SAS) and the assessment using BIS in ventilated and sedated ICU patients.

Methods

ICU patients requiring mechanical ventilation and sedation were monitored using the SAS and BIS. Nurses initiated event markers with BIS at the time of SAS assessment but were blinded to BIS scores.

Results

Data were collected on 40 subjects generating 209 paired readings. Moderate positive correlation between BIS and SAS values was shown with a Spearman Rank coefficient r value of .502 and an r² of .252 (P < .0001). Wide ranges of BIS scores were observed, especially in very sedated patients. Strong positive correlation was noted between BIS and electromyography with an r value of .749 (P < .0001). Age and gender significantly influenced BIS/SAS correlations.

Conclusion

In situations in which the clinical assessment is equivocal, BIS monitoring may have an adjunctive role in sedation assessment. BIS values should be interpreted with caution, however, because electromyography activity and other factors seem to confound BIS scores. More research is necessary to determine the role of BIS monitoring in ICU practice.