Motor-evoked potential monitoring

Several techniques for intraoperative monitoring of spinal cord motor tracts have been developed recently. The aim of this review is to describe the essentials of these techniques, recent advances and the indications and limitations of the various modalities. While transcranial cortical stimulation with recording of myogenic responses is entirely specific for motor tract conduction, it is also the most challenging motor tract monitoring technique in terms of anaesthetic management, because it is incompatible with high concentrations of volatile agents and requires careful titration of neuromuscular blocking drugs. Nerve action potentials recorded following high thoracic spinal cord stimulation are robust even in the presence of 1 minimal alveolar concentration of isoflurane or desflurane, but the recorded signal may not be entirely specific for motor tract conduction. Multi-pulse stimulation paradigms appear to improve the amplitude and reproducibility of motor-evoked potentials in response to both transcranial and spinal cord stimulation. The use of these techniques will probably improve the success rate and reliability of intraoperative motor-evoked potential monitoring.