Effects of the auditory stimuli of an auditory evoked potential system on levels of consciousness, and on the bispectral index

Investigators in the field of depth of anaesthesia monitoring sometimes measure the auditory evoked potential (AEP) and the Bispectral Index (BIS) concurrently. However, the auditory stimuli required to generate an AEP may increase the level of consciousness, and cause an increase in the BIS. They may also alter the BIS by producing phase-locked harmonics in the surface electroencephalogram. The aim of this study was to determine if AEP stimuli have clinically significant effects on levels of consciousness and BIS values during sedation and general anaesthesia. Ten healthy adult patients were studied by measuring and recording the BIS for 6 epochs of 5 min each. The first 3 epochs took place during steady-state sedation, during which time the Observer's Assessment of Awareness/Sedation (OAA/S) score was also measured. The second 3 epochs took place during steady-state anaesthesia. During alternate epochs, patients were subjected to the auditory stimuli generated by an AEP system. The auditory stimuli were not associated with a change in BIS values (during sedation and anaesthesia) or OAA/S scores (sedation).