Auditory evoked potentials index versus bispectral index during propofol sedation in spinal anesthesia

It is still controversial whether an electroencephalogram could be a useful monitor of sedation levels. The present study was performed to compare the bispectral index (BIS) and the auditory evoked potentials index (AAI) during light sedation with propofol infusion in spinal anesthesia.

Eighty patients, aged 20 to 70 years, scheduled for surgery of the lower extremities under spinal anesthesia were assigned to one of four groups (20 patients each). Patients in the AAI propofol and BIS propofol groups were sedated with propofol infusion at an initial rate of 2 mg x kg(-1) x h(-1). Propofol infusion was controlled to try to keep the observer's assessment of alertness/sedation (OAAS) scale at 3 or 4. Patients in the AAI control and BIS control groups did not receive propofol.

The OAAS scales and the AAI or BIS decreased significantly in all groups during surgery, while the decrease was larger in the AAI propofol and BIS propofol groups. The AAI was significantly lower along with lower OAAS scales. There was no overlap in the AAI between OAAS scale 3 and scale 5 in the AAI propofol group, while in the BIS propofol group, no difference was observed in the BIS among OAAS scales 2, 3, 4, and 5.

The AAI, but not the BIS, could discriminate slight changes of consciousness during light sedation with propofol infusion in patients with spinal anesthesia.