• Bertram C A Scheller, Michael Daunderer, and Gordon Pipa.
• Clinic for Anesthesiology, Intensive Care Medicine and Pain Therapy, Johann Wolfgang Goethe University, Frankfurt am Main, Germany. scheller@em.uni-frankfurt.de
• Anesthesiology. 2009 Aug 1; 111 (2): 340-55.

BackgroundBrainstem auditory-evoked responses (BAEP) have been reported to be unchanged in the presence of drugs used for induction and maintenance of general anesthesia. The aim of this study was to investigate if the signal segments after the auditory stimulus that are used to average the evoked response change under the influence of general anesthesia.MethodsBAEPs of 156 patients scheduled for elective surgery under general anesthesia were investigated. Anesthetic regimen was randomized as a combination of one of four hypnotic drugs supplemented by one of four opioids. Signal segments after the auditory stimulus were obtained at six different periods of anesthesia. Power and phase properties of wavelet-filtered single-sweep auditory-evoked activity accounting for the waveform of the averaged BAEP wave V and the stability of amplitude and latency of the averaged BAEP wave V over periods were analyzed.ResultsAmplitude and latency of wave V change slightly with no significant difference between the periods. During anesthesia, however, the power of single sweeps is significantly reduced, whereas phase-locking properties of the according signal segments are significantly enhanced. This effect is independent of the anesthetic or opioid used.ConclusionsGeneral anesthesia affects phase and power of the segments of the electroencephalogram related to BAEP wave V. This study's results support the idea that temporally precise responses from a large number of neurons in the brainstem might play a crucial role in encoding and passing sensory information to higher subcortical and cortical areas of the brain.

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