Elsevier

Heart & Lung

Volume 38, Issue 4, July–August 2009, Pages 336-345
Heart & Lung

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

https://doi.org/10.1016/j.hrtlng.2008.10.010Get rights and content

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.

Section snippets

Background and Literature Review

The BIS monitor was developed in the 1990s to monitor the effects of anesthetics and other drugs on the brain during surgery.2, 3 Early studies of BIS monitoring in the operating room setting suggested that BIS identified patients at risk of awareness during surgery, improved drug therapy, lowered costs, and shortened recovery times.4, 5, 6, 7, 8 In more recent studies, however, some researchers have concluded that BIS monitoring is not sensitive enough to accurately monitor depth of sedation

Study Objectives and Rationale

The overall aim of this study was to evaluate the use of the Bispectral Index (BIS) in monitoring sedation in ventilated ICU patients. The specific aim of this study was reflected in the following research question: What is the relationship between BIS monitor (objective measure) and the SAS (subjective measure) assessment of sedation in mechanically ventilated patients?

Setting and sample

A prospective, descriptive correlation design study was conducted in a 12-bed medical intensive care unit (MICU) in a 780-bed acute care facility. This study was approved by the health care system's institutional review board, and formal written consent was waived.

Adult critical care patients admitted to the MICU were selected by convenience sampling. Inclusion criteria included patients 18 years or older who required mechanical ventilation and sedation with a baseline intact brain function.

Results

Data were collected from 40 subjects with ages ranging from 25 to 86 years, with a mean of 62 years. Approximately 53% were female, and more than 87% were Caucasian. The most common medical diagnoses for the subjects were acute respiratory failure, septicemia, pneumonia, cerebral artery occlusion, myocardial infarction, and acute renal failure. The mean APACHE II score for subjects was 24.5, with a range from 8 to 37 (Table III). All subjects received sedation, and approximately one third

Discussion

In this study yielding 209 paired readings, a moderate positive correlation between BIS and SAS was found. The mean BIS scores for SAS levels 4 and 5 were clearly higher than those for SAS levels 1, 2, and 3. Our mean BIS score for SAS level 4 (calm) was 80.4, similar to the BIS 79 for SAS level 4 reported by Simmons et al,21 and somewhat lower than the BIS 87 found by Riker et al.23

The correlations between BIS and SAS scores in previous studies have ranged between r = .26 and r = .85.31, 34

Limitations

Potential limitations to the internal validity of this study relate to reliability of measures and sampling. First, the assessment of the level of patient sedation using the SAS was performed by different staff nurses with varying degrees of clinical experience. Determination of the SAS score is itself subjective and potentially limited by interrater variability. In addition, documentation of the SAS was not consistently recorded per guideline recommendations. Second, data from the BIS monitors

Conclusions

A reliable, valid, and easy-to-use objective measure of sedation in ICU patients would unquestionably decrease errors in sedation assessment and therefore improve patient care. The BIS-XP has been proposed as such a measure, but correlations with subjective sedation assessment measures have been less than optimal in most studies. The results of this study contribute further evidence that BIS scores are not effective as the sole measure of sedation in ventilated ICU patients.

On the basis of

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  • Cited by (0)

    This research was funded by the American Association of Critical Care Nurses/Sigma Theta Tau Critical Care Research Grant.

    This research was performed at Christiana Care Health System in Newark, Delaware.

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