The ability of Mid Latency Auditory Evoked Potentials for a routine monitoring of sensory suppression should be evaluated during a wide spectrum of clinically common forms general anesthesia.

Up to now there is no fully functional and precise technique for accurate assessment for monitoring the degree of unconsciousness during general anaesthesia. Previous studies and results obtained during the project regarding the effect of anaesthetics on single neurons and small neuronal networks indicate that it would be most promising to use a method directly correlating to the integrity of the relevant functional systems. As one goal of the project it was formulated to develop and test a new system for recording and analysis of mid latency auditory evoked potentials (MLAEP), suitable to be used in the clinical surrounding of an operation theatre. Step by step an investigational system was developed, that after obtaining legal approvement was functional in a broad spectrum of cases. In a multicenter study the including 4 clinical centres and 426 patients the reliability of the system was proved. Even under the hard conditions of the OR the apparatus was able to record the signals with sufficient reliability and precision. A clear correlation of MLAEP parameters with clinically defined states of consciousness could be identified. Differences in the effect of the used combinations of general anaesthetics and opioids were identified. An algorithm for automatic analysis of the signals was developed, to allow users with limited knowledge of interpretation of MLAEP signals to use them for monitoring anaesthesia.

Inclusion Criteria:

• Male and female patients
• Scheduled for elective urological, gynaecological or general surgery
• ASA status I or II
• Age 18 to 65

Exclusion Criteria:

• ASA status above II
• Operative procedures involving the neurocranium, neck or require other neurophysiologic monitoring
• Inability to communicate freely in the german language
• Major hearing deficit
• Regular centrally acting medication including drug abuse within 3 months prior to the investigation
• Participant of an other clinical investigation
• Lacking or withdrawal of written informed consent