title: Intraoperative evoked potential monitoring of the spinal cord: enhanced stability of cortical recordings.
abstract: Intraoperative EP monitoring of spinal cord function depends upon a quickly obtained, reproducible EP. The records must be obtained in a hostile environment where artifacts and other sources of electrical noise cannot easily be eliminated: records are obtained continuously without interrupting the surgery. We studied EP reproducibility by measuring cortical EP amplitude range and latency range within individual patients. Reproducibility was enhanced by several changes in the stimulus and recording parameters: (1) Bipolar recording near the vertex (Cz-Pz, E1-E2) eliminated a significant amount of the artifacts and random variations seen in referential recordings. Bipolar recordings sacrifice some amplitude but the improved reproducibility is worthwhile. (2) Restricted filters (especially 30-3000 Hz) improve reproducibility still further, compared to the traditional open filters (1-1000 Hz). (3) Fast stimulation rates improve monitoring up to rates of about 5 stimuli/sec. At even faster rates too much amplitude attenuation usually occurs. Using these techniques stable intraoperative EPs were recorded from all 115 patients except those in whom EPs were abnormal even before surgery. Advantages and disadvantages compared to epidural recording techniques were discussed. Several further observations were made, including (1) monitoring could be done equally as well with stimulation either at the peroneal or at the posterior tibial nerve; (2) balanced nitrous oxide and narcotic anesthesia did attenuate EPs by about 60%, although this is not so much as to interfere seriously with monitoring.
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D004569:Electroencephalography; D005071:Evoked Potentials; D006801:Humans; D007430:Intraoperative Care; D008875:Middle Aged; D013116:Spinal Cord / Q000503:physiopathology*; D013118:Spinal Cord Diseases / Q000601:surgery*