Bilateral measurement of bispectral index and mid-latency auditory evoked potentials in patients with unilateral brain lesions

Purpose

The impact of intracranial lesions on the results of bispectral index (BIS) and mid-latency auditory evoked potentials (MLAEP) remains unclear. We tested the hypothesis that MLAEP (latencies of wave Pa and wave Nb) obtained bilaterally from patients with unilateral brain lesions result in less bias than BIS values obtained from both sides.

Patients

Twenty patients with unilateral supratentorial lesions were included in the study.

Materials and Methods

Bispectral index and MLAEP were measured bilaterally using the BIS and AEP modules of the Monitor S/5 (GE, Helsinki, Finland). Significance of the difference in the number of patients with a clinically relevant bias (more than 10%) of BIS and MLAEP was calculated by Fisher exact test.

Results

Bispectral index was significantly in more patients different on the side of the lesion than latencies of wave Pa and Nb (18 patients for BIS, 1 patient for Pa, 3 patients for Nb, P < .0001). Mean bias was −18.8 ± 25.7 for BIS, 1.5 ± 3.4 milliseconds for wave Pa, and −1.5 ± 6.1 milliseconds for wave Nb (data given as mean ± SD).

Conclusions

Mid-latency auditory evoked potentials are less biased by intracranial lesions than BIS and seem to be superior to BIS for the monitoring of patients with intracranial lesions.