The auditory steady state response during sufentanil anaesthesia.

The auditory steady state response (ASSR) is a sinusoidal evoked potential elicited by rapidly repeated auditory stimuli. The ASSR was recorded in eight patients during high-dose sufentanil anaesthesia for cardiac surgery in order to assess its usefulness as a measure of the level of consciousness. The electroencephalogram (EEG) was recorded for comparison. The ASSR was present before induction in all patients. It was attenuated severely or possibly abolished with loss of consciousness, and reappeared at low amplitude 5-10 min later and remained attenuated until the end of surgery. The amplitude increased with early signs of awakening in the Intensive Care Unit. With few exceptions, changes in the simultaneously recorded EEG were similar to those of the ASSR. The ASSR deserves further evaluation as a tool for monitoring level of consciousness during high-dose opioid anaesthesia.