Motor Evoked Potentials: Issues in Safety and Operative Monitoring

Abstract

The monitoring of the motor system is an important goal for spinal cord evaluation. Ideally we need a safe procedure, easily used, reliable, and able to indicate problems with the upper or lower motor neuron pathways. Until a few years ago little was available in such a direction. However, the advent of both spinal cord stimulation and transcranial motor pathway stimulation has offered the opportunity to develop such testing. A particularly useful type of transcranial stimulation in the awake patient is the magnetic stimulator, first described in 1985 by Dr. Anthony Barker. This stimulator was initially limited by the large surface area of brain which it stimulated, and by the fact that it was just powerful enough to stimulate awake patients. Therefore it was often not reliable on an anesthetized patient with a higher stimulus threshold. The technology of these devices is evolving rapidly, and more powerful stimulators are being tested by Novametrix and Cadwell Labs, as well as some other groups. The one which has been initially evaluated for the operating room is the Cadwell MES-10. This can stimulate patients in the operating room under some conditions.