Correlation of Bispectral Index with Glasgow Coma Score in mild and moderate head injuries.

BACKGROUND

Bispectral Index (BIS) derived from electroencephalogram (EEG) is primarily developed to monitor the depth of unconsciousness. Recent evidence suggests that BIS may also help in the detection of cerebral ischemia and prognostication of outcome of traumatic brain injury (TBI). The present study was designed to investigate the correlation between Glasgow Coma Score (GCS) and BIS in mild and moderate head injury.

METHODS

In 29 patients with mild (GCS 13-15) and moderate (GCS 9-12) head injuries who underwent craniotomy, GCS and BIS were measured before surgery, after surgery and once a day for the first 10 days.

RESULTS

A significant correlation was found between GCS and BIS in the data sets from all the patients (r = 0.67; p < 0.001). Mean BIS values increased with increasing GCS scores. However, the scatter of BIS values for any GCS score was high limiting the value of BIS in predicting GCS. Mean BIS values were significantly different between mild and moderate head injuries [65.7 +/- 16.1 vs. 85.7 +/- 6.1, p = 0.006].

CONCLUSION

In patients with mild and moderate head injury, significant correlation exists between GCS and BIS. But the high degree of scatter of BIS values for any given GCS score limits its use as a monitor of depth of coma in TBI. Further studies are required to understand the relation between BIS algorithm and cerebral electrical activity following TBI to define the role of BIS as an electrophysiological correlate of consciousness in TBI.