IONM/Spine

Question 1

purpose of IONM

Answer 1

-protect integrity of peripheral and central nervous systems during surgical manipulation

Question 2

What is the order of most to least sensitive IONM modalities (from anesthetic impacts)

Answer 2

MEP>EEG/SSEP>BAEP

Question 3

what are evoked potentials (EPs)/purpose

Answer 3

-electrical potentials that are measures in response to a particular stimuli
-used to guide surgical strategy and warn team of neurologic deficits
-can prevent irreversible damage

Question 4

4 types of stimuli used for EP studies

Answer 4

auditory, visual, motor, somatosensory

Question 5

4 surgical factors that can impact EPs (not anesthetics)

Answer 5

1. electrocautery (heat) injury to neural structures
2. mechanical stress/retraction
3. ischemia (ligation, edema, vessel damage)
4. loss of functional integrity (transection)

Question 6

what is the elastic limit of nerves and what does this mean

Answer 6

20%, further stretching can cause irreversible damage

Question 7

amplitude

Answer 7

-measurement of the intensity of evoked response to the signal
-measured in micro or millivolts (MEP)
-height of the waveform relative to baseline voltage

Question 8

latency

Answer 8

-indicative of the time necessary for the evoked response to be measured in the brain
-measured in milliseconds
-represents the delay in response to stimulus, indicated how long it takes for the signal and response to travel along the neural pathway

Question 9

what % changes in latency and amplitude suggest ischemia

Answer 9

50% decrease in amplitude or 10% increase in latency

Question 10

type of anesthetic agents that depress EP waveforms in a dose dependent manner

Answer 10

-inhalation
-IV also does but to a lesser extent
(when IA and IV are used together, the depressant effect is synergistic on SSEPs)

Question 11

what pathway does SSEP monitor

Answer 11

sensory pathway through DRG and posterior column

Question 12

Effect of each on SSEP…
Inhalationals
IV
Ketamine
Etomidate

Answer 12

-senstiive to all IA
-less affected by IV
-ket and etomidate increase amplitude

Question 13

4 common types of surgeries SSEP is used for

Answer 13

spine (wide variety), CEA, some intracranial tumors, some CV surgeries

Question 14

SSEP: drugs that decrease amplitude and increase latency (5)

Answer 14

1. halogenated agents
2. N2O
3. barbiturates (ok w/ burst suppression on EEG)
4. propofol (least pronounced, still the best IV agent to use with SSEP)
5. opioids (mild, occurs more with bolus vs gtt, still ok to use)

Question 15

how does ketamine affect SSEP

Answer 15

inc amplitude, no change in latency

Question 16

how does etomidate affect SSEP

Answer 16

increased amplitude and increased latency

Question 17

do benzos affect SSEP

Answer 17

minimally

Question 18

what pathway does MEP monitor

Answer 18

motor pathway…motor cortex, corticospinal tract, nerve root, peripheral nerve

Question 19

should you use NMBDs with MEP

Answer 19

no

Question 20

can you use inhalationals with MEP

Answer 20

over 0.5 MAC signals are suppressed –> Use TIVA

Question 21

who should not undergo MEP via magnetic stimulation?

Answer 21

patients with spinal or bladder stimulators, metallic foreign bodies, pacemakers, previous craniotomy

Question 22

what part of the spinal cord would MEP signal reflect poor perfusion of

Answer 22

anterior spinal cord

(bolded in the slides)

Question 23

2 drugs contraindicated with MEP

Answer 23

Magnesium and NMBDs

(MMNM: MEP, mag, neuromuscular)

Question 24

What type of anesthesia is contraindicated with IONM

Answer 24

Regional: spinal AND epidural

Question 25

4 patient related factors that can affect EPs

Answer 25

Hypothermia
Hypotension
Anemia
Positioning