Intraoperative spinal cord monitoring with spino-spinal evoked potentials

Abstract

During the past eight years we have conducted intraoperative spinal monitoring in 56 cases of spinal or spinal cord surgery to prevent postoperative neurological complications using spino-spinal evoked potentials with electrical stimulation. This paper describes our experience with intraoperative changes of the evoked potentials. To detect changes of spinal cord function during spine or spinal cord surgery many investigators had reported different experimental or clinical methods. In 1972, Vauzelle described the useful intraoperative wake-up test for patients operated upon for severe spinal deformity¹. Anaesthesia was adjusted for the wake-up test which allowed sufficient dissociation of pain and consciousness to permit spontaneous motion of the extremities in partial or temporary awakening during the course of anaesthesia. In 1984 Brown² reported the intraoperative use of somatosensory cortical evoked potentials to monitor spinal cord function during 300 orthopaedic surgical procedures. Brown described disadvantages of this method in which the wave-forms were frequently affected by medications and anaesthetic agents. Spino-spinal evoked potentials (S-SEPs) which are observed following direct stimulation of the spinal cord, from recording electrodes placed on the dura, has been developed mainly in Japan since 1972. These potentials are characterized by a high amplitude and sharply shaped wave-forms and changes in the potentials can be more easily evaluated. In 1983 Jones³ reported 115 patients who underwent Harrington instrumentation and were monitored by spinal SEPS from the epidural space. Jones concluded that spinal somatosensory evoked potentials are sensitive to minor spinal cord impairment. Recently in order to monitor descending pathways during surgery, motor evoked potentials have been recorded from thenar muscles and from the epidural space. Recently, noninvasive motor cortex magnetic stimulation has become popular in Japan.