[Technical problems in intraoperative monitoring of sensory evoked potentials]

Recent advances in both the equipment and the recording technique of sensory evoked potentials (EP) have brought high levels of versatility and reliability of objective measurement to the assessment of nervous system function. They have also allowed the use of intraoperative evoked potentials. The operating room, however, is usually considered a hostile environment, where various kinds of artifacts from surgical manipulation and generated by electrical armamentaria disturb electrophysiological recordings. Although several authors have reported on intraoperative EP monitoring, they have described few of the practical details of recording techniques. Having developed an intraoperative recording technique for evoked potentials over the past 3 years, we present the technical measures taken to overcome interference and obtain sufficiently stable and reliable EP recordings for intraoperative monitoring. All electrical equipment used in the operating rooms must, of course, be grounded securely. Even after grounding in the usual manner, however, artifacts appeared intermittently. The source was found to be a Mayfield-Kees three-pin head rest and a self-retaining retractor, both of which seemed to pick up electromagnetic radiation originating from electrocauteries and others. These artifacts could be minimized by grounding the head pins all each point of insertion into the patient's head and by use of a silicon-coated spatula rather than a metal one. In addition automatic artifact rejection by voltage overload sensing seems to be indispensable to eliminate the effect of extraneous mechanical and electrical interference which occur inevitably in surgical procedures.(ABSTRACT TRUNCATED AT 250 WORDS)