Monitoring Evoked Potentials

Question 1

What is a diminutive human being without any deformity of physiology?

Answer 1

homunculus

Question 2

Where do the sensory and motor locations reside?

Answer 2

cortex

Question 3

What is the arrow pointing to?

Label the shaded areas and describe its location relative to the brain.

Answer 3

cerebral longitudinal fissure

Central sulci
Motor area is more frontal than the sensory area.

Question 4

What does SSEP represent?

Answer 4

somatosensory evoked potential

Question 5

If want to monitor SSEP for the feet and legs, what electrodes would be used?

Answer 5

C2, C3, and C4

(C = central sulci)

Question 6

What defines the somatosensory pathway? (2)

Answer 6

Dorsal (posterior) horns = sensory pathway

Ventral (anterior) horns = motor pathway

Question 7

Which field will generate an impulse first for SSEP? Far or near field?

What do we try to minimize affecting regarding SSEP monitoring?

What could “P” and “N” possibly represent in an SSEP graph?

Answer 7

Far field occurs earlier (Note: Near field would be considered the cortex.)

Latency and increase amplitude of evoked responses

P = positive excursion, N = negative excursion

Question 8

Monitoring evoked potentials from the ______ will generate an increased amplitude and decreased latency waveform.

Answer 8

arms rather than the legs

There is less resistance from the arms to the head than from the legs to the head.

Question 9

What nerves are monitored in SSEP? (2)

Answer 9

Left median nerve

Left tibial nerve

Question 10

Random activity is generated from an evoked response. How is this activity suppressed?

Answer 10

by averaging the potentials

Question 11

What can anesthetic drugs do to produce a change in sensory and motor evoked potentials?

Answer 11

Can be mistaken for a surgically induced change

Question 12

What anesthetic drugs do NOT affect SSEPs? (5)

Answer 12

Etomidate
Droperidol
Ketamine
Opiates
Dexmedetomidine

Question 13

What anesthetic drugs do NOT affect transcranial MEPs? (4)

Answer 13

Etomidate
Ketamine
Opiates
Dexmedetomidine

Question 14

What anesthetic drugs DO affect transcranial MEPs? (4)

Answer 14

Barbiturates
Diazepam
Midazolam
Volatile agents

Question 15

What affect do volatile agents have on latency and amplitude?

Answer 15

Dose dependent increase, volatiles have the greatest effect of all drugs.

It causes the greatest increase on latency and greatest decrease in amplitude.

Question 16

How will N2O affect latency and amplitude?

Answer 16

Increases latency slightly, greater decrease in amplitude

Question 17

What effect does etomidate have on latency and amplitude?

Answer 17

Increases latency slightly with a pronounced increase in amplitude.

Question 18

What effect do narcotics have on SSEPs?

Answer 18

MAY increase latency with no effect on amplitude.

Bolus transiently increases latency. Continuous has little effect.

Question 19

What drug may have been infused to produce the changes in amplitude?

Answer 19

Etomidate which increases amplitude if its puny.

Question 20

How can you remove ECG interference from SSEPs?

Answer 20

The tachycardia alarm can be fixed by turning on the pacer detect mode.

Question 21

What is BAEP/BAER/BSER?

What nerve is stimulated?

Answer 21

Brainstem auditory evoked potential/response)

CN 8, auditory

Question 22

What anesthetics should not be used during BAEPs?

Answer 22

We can use all of them.

Question 23

What are the guidelines for choosing anesthetics during BAEPs?

Answer 23

IV agents have significantly less effect than “equipotent” doses of inhaled agents

Combinations of drugs produce additive effects

Subcortical (spinal/brainstem) sensory evoked responses are very resistant to effects of anesthetic drugs.

Question 24

______ responses, because they are entirely cortical suffer the greatest sensitivity to changes in anesthetic drug levels.

Answer 24

VEP (visual evoked potentials)

Question 25

What spinal horns do motor evoked potentials (MEPs) ellicit?

Answer 25

ventral (anterior) horns

Question 26

Motor deficits after _______ or _______ may occur without changes in SSEPs.

So, what do you do?

Answer 26

spinal surgery

aortic cross clamping

Motor evoked potentials allow monitoring of pathways not involved in sensory transmission.

Question 27

What IV agents produce less depression effect on MEPs? (5)

Answer 27

Propofol
Ketamine
Etomidate
Opiates
Dexmedetomidine

Question 28

What muscles are monitored during MEPs if working around the ear for example?

Answer 28

Orbicularis

Orbicularis oris

Question 29

What facial nerves are monitored?

Answer 29

Trigeminal (CN V)

Facial (CN VII)

Question 30

What is the name of the test for neurologic monitoring?

Answer 30

Wake-up test

Question 31

Monitors of the nervous system can monitor function or adequacy of blood flow, or both. True or false?

Answer 31

True

Question 32

Most anesthetic drugs have a typical effect on the EEG: small doses produce activation, moderate doses produce slowing with maintenance or increase in amplitude, and large doses produce burst suppression. True or false?

Answer 32

True

Question 33

EEG changes associated with inadequate CBF are similar to increasing doses of most anesthetic drugs. True or false?

Answer 33

True

Question 34

Anesthetic effects on cortical SERs are significant and render monitoring difficult. True or false?

Answer 34

True

Question 35

Subcortical responses (auditory, somatosensory) are resistant to effects of anesthetics. True or false?

Answer 35

True

Question 36

What may help detect significant risk of stroke at any time during the perioperative period?

Answer 36

transcranial doppler

Question 37

Cerebral oximetry is a new technology designed to measure the adequacy of CBF. However use of the device remains controversial. True or false?

Answer 37

True, since there is no universal agreement about normal perioperative changes.