Can the bispectral index monitor quantify altered level of consciousness in emergency department patients?

OBJECTIVES

A daily part of emergency medicine practice includes assessing patients with altered levels of consciousness (ALOC). The authors hypothesized that a bispectral index monitor (BIS), a processed electroencephalographic monitor traditionally used to monitor patients under anesthesia, would represent an objective quantification of impairment of consciousness. They compared the BIS score with the Glasgow Coma Scale score (GCS) in emergency department (ED) patients with ALOC.

METHODS

The authors performed a convenience sampling of ED adults presenting with ALOC (GCS <or= 14). Patients with abnormal baseline mental status were excluded, as were those who were unable to tolerate the forehead BIS leads. The blinded BIS value was recorded after the treating physician assigned a GCS to the patient. The BIS and GCS measurements were then correlated.

RESULTS

Data were obtained for 38 patients (20 male, 18 female). The median age was 42 years (range 14 to 93 years). Despite being statistically significant (p = 0.0165), the correlation between the GCS and the BIS score was only moderate (Spearman's rho = 0.387) and displayed wide variability. For example, when the GCS was between 3 and 5, the corresponding BIS scores ranged from 47 to 98. When the GCS was between 12 and 14, the corresponding BIS scores ranged from 56 to 98. Receiver operating characteristic curves for BIS at each GCS threshold demonstrated low discriminatory power (areas under the curve range 0.61 to 0.73).

CONCLUSIONS

BIS monitoring does not reliably correlate with GCS in ED patients with ALOC, and does not appear to have potential to accurately quantify impairment of consciousness in this setting.