Why Does Threshold Level Change in Transcranial Motor-evoked Potentials During Surgery for Supratentorial Lesions?

Abstract

Pneumocephalus was the only factor associated with increase in threshold level during MEP monitoring without damaging motor pathway. Threshold level on the affected side can rise up to 48% without being predictive of postoperative paresis, as long as the difference between the increased threshold of the affected and unaffected side is within 20%. Changes in systolic or mean blood pressure within a range of 20 mm Hg do not seem to influence intraoperative MEP.