ACNS TceMEP Guidelines

MEPs or TceMEPs stand for _____ _____ stimulation motor evoked potentials

transcranial electrical

MEPs monitor the _____ tract, which includes the pyramidal tract and (dorsal/ventral) portion of the spinal cord.

corticospinal, ventral

MEPs are defined as high intensity (direct/indirect) cortical stimulation through an intact skull, which means that electrodes are placed on the brain surface using LOW intensity

direct

transcranial magnetic stimulation (TMS) is used for clinical (awake/asleep) subjects.

awake

What is a positive Babinski sign?

upper motor neuron lesion, where the big toe dorsiflexes and other toes fan out from a noxious stimuli on the sole of the foot. normal reflex shows PLANTAR flexion (toes curling in) with the noxious stimuli. Can be unilateral or bilateral

A positive Babinski sign is (normal/abnormal) in infants due to incomplete myelination of the corticospinal tracts.

normal

lower motor neuron lesions can be noted from ____ (involuntary muscle contraction or twitch) of muscles, or ____ (no muscle tone and no movement). Deeper areas can be detected by ____ testing, though they can happen in any skeletal muscle in the body

fasciculations and flaccid paralysis. EMG

TMS is a practical technique for MEP studies in awake subjects. Induces electrical current within the brain tissue and therefore (does/does not) pass large amount of current through the scalp, using (D-waves/I-waves)

does not, I-waves

Since TMS uses I-waves, and anesthesia suppresses I-waves, it is not ideal for (clinical/intraoperative) settings where patients are asleep. Also, it is difficylt to maintain a constant position of the magnetic coil relative to patient’s head.

intraoperative

D-waves are ____ activation of the pyramidal cell axons that leave cortex and comprise corticospinal tract. Since D-waves don’t monitor neurons with ____, they are insensitive to anesthesia and great for intraoperative settings. I-waves are ____ activation of synaptic transmission from activated cortical interneurons. Both are recorded from (muscles/nervous system).

direct, synapses, indirect. nervous system

What are M-waves?

myogenic MEPs, also known as CMAPs, that are recorded from muscles.

Amplitude of D-waves are higher in the ____ region than the ____ region of the spinal cord because of the small number of corticospinal tract fibers, or white matter, that remains - many of the nerves have already exited to innervate their corresponding muscles! Because of this, it is not practical to monitor below the ___ level, where spinal cord begins tapering off.

cervical, thoracic. T10

Because I-waves involve synapses, there may be (one/multiple) I-wave(s), which reflect the number of synapses between the interneurons that are initially activated by the stimulus and the pyramidal neurons that give rise to the corticospinal tract. Since I-waves are mediated by (cortical/corticospinal) synaptic activity, they are markedly (reduced/increased) by anesthesia.

multiple, cortical, reduced

Epidural electrodes can be placed at the (rostral/caudal) site relative to the region at risk, while an additional electrode may be placed (rostral/caudal) to the surgical field as a control. If only ONE electrode is used, it is critical to place it (rostral/caudal) to the surgical field, since MEPs monitor a (ascending/descending) pathway.

caudal, rostral, caudal, descending

A normal response involves both rostral/control and caudal/below surgical field responses present, while a surgical problem involves the (rostral/caudal) wave being absent and a technical problem involves the (rostral/caudal) wave being absent, or both waves being absent

caudal, rostral

A spacing of 2-3 cm between epidural electrodes (rostral and caudal) is recommended to avoid ____

noise

The most common technical issue with epidural electrodes is ____ from fluid over the electrode, which will require draining.

shunting

CMAPs stand for (complex/compound) muscle action potentals

compound

What is a train?

repetitive succession of impulses used to stimulate motor cortex

Trains are required to ____ excitatory postsynaptic potentials in the anterior horn cells in order to bring them to threshold.

summate

larged amplitude CMAPs are typically displayed by the most (distal/proximal) muscle group, and proximal muscles tend to give (more/less) reliable MEPs.

distal, less

For the upper limb, MEPs are optimally recorded from hand muscles (thenar and ADM), while for the lower limb MEPs are optimally recorted from tibialis anterior and abductor hallucis - true or false

true

when thoracic or lumbar spinal cord is at risk, upper limb MEPs may be used as a ____

control

if thoracic spine is at risk, lower limb MEPs are (recommended/not recommended)

recommended

if lower spinal cord/cauda equina is at risk, an*l sphincter MEP (should/should not) be recorded

should

Transcranial electrical stimulation predominantly generate myogenic MEPs (ipsilateral/contralateral) to the stimulating anode.

contralateral

M Wave responses are a combination of direct and indirect waves, but are not called this, since they are not recorded over neural tissue. true or false?

true

Patients with rare congenital motor tract NON-decussation produce predominantly (anode/cathode) ipsilateral myogenic MEPs

anode

M-waves may also be elicited by stimulation of cortex under the TceMEP cathode, but such responses are (more/less) stable.

less

D-waves are (large/small) and require signal averaging, but do not require (single pulse/multi pulse) activation. In contrast, myogenic MEPs are (large/small) and thus do NOT require signal averaging. They require a ____ of stimulus pulses, and because they are affected by NMBAs, they are (sensitive/insensitive) to anesthesia.

small, multipulse (D-waves are single-pulse). large, train, sensitive.

D-waves record muscle responses from both sides, which we said can lead to a false negative or failure to detect (unilateral/bilateral) compromise.

unilateral

Myogenic MEPs record responses from muscles on each side separately, so are less prone to false negatives than D-waves. They assess (gray/white) matter which may be more sensitive to ischemia, and may also demonstrate nerve root/peripheral nerve dysfunction. As a result, the myogenic MEPs may be lost while D-waves remain.

gray

D-waves are (consistent/inconsistent) run to run, while myogenic MEPs are (consistent/inconsistent) run to run.

consistent, inconsistent

Are MEPs more sensitive to inhalational agents (subpar anesthetic regimen) than SSEPs?

yes - they can be lost (or we see significant decrease in amplitude) if the anesthetic regimen is changed

Posterior myelotomies to remove intramedullary tumors that develop in (neurons/glial cells) within spinal cord may result in impairment of (SSEPs/MEPs), leading (SSEPs/MEPs) to become more important

glial cells, SSEPs, MEPs.

For posterior myelotomies, we monitor which three moedalities?

SSEPs, MEPs, EMG

For MEPs, we use (needle/corkscrew/both) needles to monitor, but prefer (needle/corkscrew) electrodes since they have lower impedances and are less likely to become dislodged. Also less likely to lead to patient injury (tissue burns).

both, corkscrew

C1/C2 or C3/C4 electrodes can both be used, but which one is preferred over the other due to the fact that it causes less facial/jaw movement? Hint: Remember, upper extremities are more lateral!

C1/C2

If no responses are elicited, the recommended relocation of the C1 and C2 stimulating electrodes is to move them more laterally, but this runs the risk of increased ____/____ movement.

face/jaw

Cz (anode) - Fz (cathode) looks at (upper/lower) limb responses only.

lower

Optimal electrode arrangement for stimulation may vary between patients and surgical circumstances - true or false?

true

Stimulation equipment for TES should be able to deliver (brief/prolonged) trains of high intensity stimuli, where the intensity of the stimulus pulses, the number of pulses per train, and the interpulse interval within the train can be adjusted by the operator.

brief

Constant ____ or ____ stimulators can be used

voltage or current

A display of the delivered current is (desirable/not desirable) and the equipment should include circuitry to limit total current delivered during stimulus train to a safe level.

desirable

What are the parameters for MEP in terms of pulse number (ACNS guidelines)?

3+ pulses

What should the interstimulus interval be, according to ACNS guidelines?

2-4 msec, or 400 Hz

• too long, and the temporal summation is lost

• too short, and the stimuli after the first pulse is not effective due to the absolute refractory period

What does sensitivity have to be, according to ACNS guidelines?

10-200 microvolts per division

What does bandpass have to be, according to ACNS guidelines?

10-2,000 Hz

What does analysis time have to be, according to ACNS guidelines?

1000 msec

What does pulse width have to be, according to ACNS guidelines?

50-75 usec, or 0.05-0.075 msec

TceMEP: great variability so a certain threshold for amplitude decrease would likely lead to false alarms, so a significant change is categorized as an (absence/presence) of response, hence the “all or nothing” name. A D-wave significant change is categorized as a 50% drop in (amplitude/latency)

absence, amplitude

• you should still notify the team if the myogenic MEP significantly decreases by around 50-90% rather than waiting until it completely disappears

opioids have (minor/major) effects on myogenic MEPs

minor

nitrous oxide produces marked changes in myogenic MEPs, but can be successfully recorded using a “nitrous/narcotic” technique. true or false?

true - as long as the nitrous is kept low

(infusion/bolus) doses should be avoided during critical periods with the aim of keeping anesthesia as steady as possible, and muscle relaxants should also be avoided

bolus

most common complication with TceMEP stimulation is (an*l/oral) injury, hence the use of padding or soft bite blocks to prevent mouth injury

oral

patient movement can interfere with surgery, so partial NMB (can/cannot) be administered. Surgeon consent is needed before running any motors, to avoid producing movement at times during the surgery where it may be hazardous.

can

electrical stimulation of the brain (can/cannot) trigger seizures, but the incidence of seizures during TES is very low

can

What are MEP contraindications, which are up to IP and surgeon discretion?

• pacemakers

• inter-cardiac defibrillators

• previous skull openings or trauma

• presence of metallic foreign bodies

• presence of indwelling neurostimulators

• history of epilepsy or seizures

Do SSEPs and MEPs predict adverse surgical outcomes?

IOM is established as an effective way to predict an increased risk of the adverse outcomes of paraparesis, paraplegia, and quadriplegia (radiculopathy not included)

What is the Stagnara wake up test? What does it run the risk of (causing to happen to the patient)?

patient is woken up during the surgery to determine functional integrity of the spinal cord, but runs the risk of extubation.