CNIM Motor Evoked Potentials (MEP)

Question 1

Transcranial electrical motor evoked potentials (tcMEPs) primarily monitor the integrity of which neural pathway?

Accepted Answer

Corticospinal tract

Answer

tcMEPs monitor the corticospinal tract (anterior and lateral funiculi of the spinal cord), which is responsible for voluntary motor control.

Question 2

The D-wave in tcMEP monitoring is generated by:

Accepted Answer

Direct activation of corticospinal tract axons at the cortex

Answer

The D-wave results from direct (D) electrical activation of corticospinal axons at the initial segment, producing a fast-conducting descending volley recorded epidurally.

Question 3

What is the standard alarm criterion for tcMEP amplitude change during intraoperative monitoring?

Accepted Answer

50% amplitude decrease or complete loss

Answer

A 50% or greater decrease in tcMEP amplitude from baseline or complete loss is the widely accepted alarm criterion requiring surgical team notification.

Question 4

Which muscle group is most commonly recorded for lower extremity tcMEP monitoring?

Accepted Answer

Tibialis anterior and abductor hallucis

Answer

The tibialis anterior and abductor hallucis are the most commonly recorded lower extremity muscles for tcMEP monitoring due to their reliable cortical representation.

Question 5

Why is total intravenous anesthesia (TIVA) preferred over volatile anesthetics for tcMEP monitoring?

Accepted Answer

Volatile agents cause dose-dependent suppression of tcMEP amplitudes

Answer

Volatile anesthetic agents cause dose-dependent suppression of tcMEP amplitudes by inhibiting corticospinal tract activity and synaptic transmission in the spinal cord interneurons.

CNIM - Certification for Neurophysiological Intraoperative Monitoring Practice Test

CNIM - Certification for Neurophysiological Intraoperative Monitoring Practice Test

CNIM Motor Evoked Potentials (MEP)