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