Spinal cord monitoring: basic principles and experimental aspects.

Spinal cord monitoring, based on spinal cord potentials recorded close to the conus medullaris and evoked by stimulating rostral spinal cord, has been extensively used clinically in Japan. To understand how such spinal cord evoked potentials (SCEP) reflect injurious effects on the spinal cord, we carried out the following animal experiments. The effects of spinal cord distraction, compression, and combined compression and hypotension or hypoxia were examined. We found that there is a critical point of compression or distraction of the spinal cord at which SCEP amplitude decreases significantly. Acute hypotension concomitant with moderate compression increases the risk of insult to the cord. Accordingly, we believe that repetitive monitoring and rapid feedback to the surgeon are indispensable to intraoperative spinal cord monitoring. Furthermore, hypotension should be carefully avoided whenever symptoms of spinal cord compression occur. A comparative study of SCEP and spinal SEP indicates that both potentials can substitute for each other, although the sensitivity of the SCEP for detecting hazardous effects is higher.