• S Zandieh, R Hopf, H Redl, and M G Schlag.
• Ludwig Boltzmann Institute for Experimental and Clinical Traumatology, A-1200, Vienna, Austria.
• Spinal Cord. 2003 Jan 1; 41 (1): 16-22.

Study DesignExperimental laboratory investigation of the effect of anesthesia on evoked potentials in rats.ObjectivesTo define the optimal ketamine/xylazine anesthesia levels for the recording of different evoked potentials.SettingBioSurgery Preclinical Department, Baxter BioScience, Vienna, Austria.MethodsRats were implanted with cranial screws that allow stimulation and recording of evoked potentials. Somatosensory evoked potentials (SEPs), brainstem-derived motor evoked potentials (BMEPs) and corticomotor evoked potential (CMEPs) were recorded under different levels of anesthesia. The recorded signals were evaluated by measuring their latencies and amplitudes. The level of anesthesia was assessed by scoring the hind limb withdrawal reflex.ResultsAll three signals showed a strong dependency on the level of anesthesia. The observed effects, however, differed between the three signals. SEP amplitudes and latencies declined as animals slowly transgressed from deep to light anesthesia. In contrast, BMEP amplitudes were larger and latencies shorter in light anesthesia than in deep anesthesia. CMEPs finally were hard to record under deep anesthesia, but were easily recorded in light anesthesia. BMEPs that were recorded during light anesthesia also showed a significant change in configuration that was coupled with a notable increase in the variability of its amplitudes.ConclusionsThe level of ketamine/xylazine anesthesia affects evoked potentials and thus should be controlled during electrophysiological recording. Our results suggest that SEPs should be best recorded during deep anesthesia, while BMEPs and CMEPs are best recorded during intermediate and light anesthesia.

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