Motor Evoked Potentials (MEP) Flashcards

Which tcMEP stimulation parameter is most commonly adjusted to optimize responses intraoperatively?

Answer: Stimulus intensity (voltage or current)

Stimulus intensity is most commonly adjusted to achieve supramaximal activation of the corticospinal tract while avoiding excessive patient movement or patient safety concerns.

Multi-pulse (train) stimulation is used for tcMEPs rather than single pulses because:

Answer: Multiple pulses summate to overcome the higher threshold of the spinal motor neurons under anesthesia

Under anesthesia, motor neurons have elevated thresholds, requiring temporal summation from a train of stimuli to reliably generate descending volleys sufficient to activate muscles.

An alarm for complete tcMEP loss in all four limbs simultaneously during thoracic spine surgery most likely indicates:

Answer: A systemic event such as hypotension, anesthetic bolus, or neuromuscular blockade administration

Simultaneous four-limb tcMEP loss suggests a systemic cause (blood pressure drop, NMB given, anesthetic change) rather than a focal surgical injury, which typically affects specific limbs.

The C3/C4 electrode positions are used for tcMEP stimulation to preferentially activate:

Answer: Upper extremity motor cortex

C3 and C4 electrode positions overlie the hand and upper extremity representation of the motor cortex, making them ideal for activating upper extremity corticospinal projections.

Relative contraindications to transcranial electrical MEP monitoring include:

Answer: Intracranial metal clips, cochlear implants, or cardiac pacemakers

Intracranial metal implants, cochlear implants, and certain cardiac pacemakers are contraindications because transcranial electrical stimulation can induce currents in these devices or cause tissue heating.

Which surgical procedure most commonly uses both SSEP and MEP monitoring together?

Answer: Thoracic and cervical spinal cord surgery

Thoracic and cervical spinal cord surgeries use combined SSEP and MEP monitoring because the two modalities provide complementary assessment of both dorsal and ventral spinal cord function.