EVOZIERTE POTENTIALE UND INTRAVENOSE ANASTHETIKA

In contrast to the electroencephalogram, which is a collection of the spontaneous brain electrical potentials generated by the cerebral cortex, evoked potentials are the electrical signals generated by the nervous system in response to brief extrinsic sensory stimuli. They can be used to establish objective evidence of an abnormality when clinical signs and symptoms are equivocal. Moreover they prove useful to define the anatomical level of lesions in the afferent pathway tested. They have been successfully applied during anesthesia and operations when pathways amenable to evoked potential recording were at risk. The most practical techniques in common intraoperative evoked response monitoring involve stimulation of visual, auditory and somatosensory pathways. As could be clearly demonstrated alterations of evoked responses can not only be found with diminished regional blood flow but in a graded manner depend on the used anesthetics as well. The potential aplication of evoked responses to monitor depth of anesthesia has been demonstrated by several groups. In contrast to visual, auditory and somatosensory cortical evoked potentials which show a large inter- and intraindividual variance acoustical evoked brainstem and somatosensory evoked subcortical potentials are very robust under general anesthesia. Drug-induced effects on shape, amplitude and latencies of evoked responses during balanced anesthesia must be well documented in order to establish evoked responses as sensitive indicators of systemic problems that may threaten the viability of the central nervous system. There is evidence that the effects on evoked responses during deep anesthetic states can be mimicked by several life-threatening conditions (e.g.: hypoxia, ischemia). This review describes the effects of intravenously used anesthetic drugs on visual, auditory and somatosensory evoked potentials and the alterations in evoked responses by abnormal systemic conditions as seen under hypotension, hypoxia, ischemia.