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IONM Training + CNIM Board Prep > SSEPs > Flashcards

SSEPs Flashcards

1
Q

Name the muscle activated with stim of the MN at the wrist

A

Thenar muscle group : Abductor Pollicis Brevis (APB)

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2
Q

Name the muscle activated with stim of the UN at the wrist

A

Hypothenar group : Abductor Digiti Minimi (ADM)

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3
Q

Define Orthodromic

A

The direction a signal normally travels

e.g. SSEPs afferent (up), tcMEPs efferent (down)

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4
Q

Define Antidromic

A

The direction opposite to which a signal normally travels

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5
Q

What happens when Stimulus Intensity is reduced?

A

Amplitude decreases

Most pronounced in Erb’s Point and Pop Fossa (peripheral responses)

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6
Q

What happens when Patient’s body temperature drops?

A

Latency increases, amplitude stays the same

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7
Q

What happens to an the Erb’s Point response during ischemia (positional, BP cuff, weighting of the head, taping of the shoulders)?

A

Both latency and amplitude decrease

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8
Q

What is the function of Erb’s Point/Pop Fossa according to the guidelines?

A

To verify adequate stimulation

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9
Q

What type of montage is best for recording subcortical or far field SSEP responses?

A

Referential

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10
Q

What type of montage is best for recording SSEP cortical responses?

A

Bipolar

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11
Q

Which peak is most susceptible to anesthesia effects?

A

N20

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12
Q

What time does EP to N20 define?

A

the conduction time between the brachial plexus and the primary sensory cortex

(aka central conduction)

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13
Q

What time does the EP latency define?

A

Peripheral conduction

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14
Q

What does EP to P14 define?

A

The conduction time between the brachial plexus and the lower brainstem

(central conduction)

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15
Q

What does P14 to N20 define?

A

The conduction time between the lower brainstem and the cortex

(central conduction)

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16
Q

Define Lumbar Potential

A

Stationary/non-propagated potential reflecting mainly postsynaptic activity in the lumbar cord from internuncial neurons (relay neurons)

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17
Q

What metal is best for Epidural Spine electrodes?

A

Platinum iridium-guards against neurotoxicity

Alternate electrodes are stainless steel or platinum

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18
Q

What is the most common technical problem with epidural electrodes?

A

Shunting from fluid over the electrode

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19
Q

What type of stimulation is best for SSEPs?

A

Constant current

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20
Q

What does an increase in stimulus intensity do to the SSEP?

A

Does not change latency, increases amplitude to a maximum

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21
Q

What is asynchronous stimulation?

A

Stimulation with delay

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22
Q

Define false positive data

A

significant changes in data, but no deficits post-operatively

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23
Q

Define false negative data

A

No changes in data, but patient has post-operative deficits

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24
Q

During upper extremity SSEP recording, the Erb’s Point electrode records data from where?

A

Brachial Plexus

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25
Q

Hypothermia of the lower extremities will result in

A

prolonged peripheral conduction time

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26
Q

What’s the most common injury during an ALIF?

A

left iliac artery injury

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27
Q

What are the dorsal column tracts for Lower Extremity SSEPs?

A

Fasciculus Gracilis, Nucleus Gracilis

Think “G” for Ground (Which is LOW)

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28
Q

What are the dorsal column tracts for Upper Extremity SSEPs?

A

Fasciculus Cuneatus, Nucleus Cuneatus

Think “C” for Clouds (which are UP)

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29
Q

What is the lumbar potential and which artery supplies the area?

A

Lower Extremity SSEP Obligate Waveform
(not commonly recorded in OR)

Stationary, post-synaptic potential generated by the Spinal Cord, Near Field Potential

Supplied by the Artery of Adamkiewicz

30
Q

What is N34 and which artery supplies the area?

A

Lower Extremity SSEP Obligate Waveform
Subcortical Response, generated by the Brainstem/Thalamus, Far Field Potential

Supplied by Basilar Artery

31
Q

What is the P37 and which artery supplies the area?

A

Lower Extremity SSEP Obligate Waveform
Cortical Response generated by the Somatosensory Cortex

Supplied by Anterior Cerebral Artery (ACA)

32
Q

What is the N9 and which artery supplies the area?

A

Upper Extremity SSEP Obligate Waveform
Peripheral Response generated by Brachial Plexus, Near Field Response

Supplied by Subclavian Artery

33
Q

What is the N13 and which artery supplies the area?

A

Upper Extremity SSEP Obligate Waveform
Stationary, post-synaptic potential generated by Upper Cervical Spinal Cord

Recorded from dorsal neck, Near Field Potential

Supplied by Posterior Spinal Arteries

34
Q

What is the N18 and which artery supplies the area?

A

Upper Extremity SSEP Obligate Waveform
Subcortical Response, Far Field response generated by Brainstem/Thalamus

Supplied by Basilar Artery

35
Q

What is the N20 and which artery supplies the area?

A

Upper Extremity SSEP Obligate Waveform
Cortical response, Near Field Potential generated by the Somatosensory Cortex

Supplied by Middle Cerebral Artery (MCA)

36
Q

What does “subcortical” mean?

A

SSEP response generated by the brainstem/thalamus

think “below cortical”

N18 Upper Extremity SSEP
N34 Lower Extremity SSEP

37
Q

N20 response recorded from CPc-Fpz

Is it a near field or far field potential?

A

Near field

38
Q

N34

Near field or far field?

A

Far field brainstem response

39
Q

Dermatomal SSEPs follow what pathway?

A

Dorsal column / Medial Lemniscus pathway

40
Q

Name the generator for the N18 waveform

A

Upper Brainstem/Thalamus

41
Q

Stimulation of what nerve(s) provides the most effective somatosensory monitoring of upper limb
positioning during prone spine surgery?

A

Ulnar & Median Nerve SSEP combined

42
Q

What is the anatomical generator of the P20 response recorded directly over the cortex during phase
reversal mapping?

A

somatosensory cortex

43
Q

Most appropriate nerve to stimulate for recording robust UE SSEPs during cerebrovascular
procedures?

A

Median nerve

44
Q

Which nucleus is the termination of the first order of the SSEP pathway for the upper extremities?

A

Nucleus Cuneatus

45
Q

The termination of the second order of the SSEP pathway is in the

A

Thalamus

46
Q

Cortical ischemia caused by the Middle cerebral artery (MCA) would cause what SSEP data changes?

A

Decrease (attenuation) of a unilateral cortical SSEP responses along with stable subcortical waveforms

(median nerve stimulation)

47
Q

If the surgeons clamps the left Internal Carotid Artery (ICA), which waveform is most likely to attenuate if the patient does not
have adequate collateral perfusion?

A

Right upper extremity (RUE) SSEP

48
Q

Injury to the SSEP pathway causes what symptoms?

A

Numbness, Loss of Vibration Sense, Loss of Conscious Proprioception

49
Q

Occlusion of which vessel is most likely to correlate with a decrease in left lower extremity cortical
SSEPs?

A

Right Anterior Cerebral Artery (ACA)

50
Q

Somatosensory evoked potentials would most likely be analyzed in the clinical diagnosis of which
condition?

  • Myasthenia Gravis
  • Multiple Sclerosis
  • Alzheimer’s Disease
  • Hydrocephalus
A

Multiple Sclerosis

Why? MS is a demyelinating disease. Demyelination causes a decrease (slowing) in the conduction velocity which would result in an INCREASE in the LATENCY of SSEP responses

51
Q

Generator for N9 Response

A

Peripheral Nerve

52
Q

Is the P37 a positive or negative response?

A

Positive

53
Q

Generator for N13

A

Spinal cord

54
Q

SSEP recordings of P37 and N45 waveforms are likely the result of stimulation to what nerve?

A

Posterior Tibial Nerve (PTN)

55
Q

SSEP recordings of N20 and P23 waveforms are likely the result of stimulation to what nerve?

A

Median or Ulnar Nerves

56
Q

During a posterior thoracic fusion, the spinal cord is injured and causes swelling. What SSEP response will remain stable despite injury to the cord?

A

The pop fossa (peripheral) response will remain unchanged following a spinal cord injury

57
Q

During a posterior thoracic fusion, the spinal cord is injured and causes swelling. What SSEP responses do you expect to observe changes from?

A

Decrease or loss of subcortical and cortical waveforms.

58
Q

Alert criteria for SSEP

A

50% decrease in amplitude

10% increase in latency

59
Q

65% nitrous oxide will cause the greatest amplitude decrease to what SSEP response?

  • N20
  • N13
  • N9
A

N20

60
Q

Ulnar nerve SSEPs can be used to detect ischemia (loss of perfusion) to what structures? (Name 3)

A
  • Limb ischemia
  • Spinal Cord ischemia
  • Cortical ischemia
61
Q

What would explain why cortical SSEP amplitudes are often smaller or less robust compared to subcortical SSEP amplitudes?

A

The thalamocortical projection adds an additional synapse before the signal reaches the
cortex, making the cortical signal more susceptible to anesthesia effects

62
Q

Following left ulnar nerve stimulation, which active electrode will produce an upward deflection at
approximately 20 milliseconds, when applied to the negative input of the amplifier?

A
63
Q

When stimulating a peripheral nerve to elicit an afferent response, the anode should be placed ___ to
the cathode

A

Anode should be placed distal to the cathode

64
Q

Erb’s point is valuable in monitoring. Give three reasons.

A
  • verify adequate stimulus
  • helps in detection of limb ischemia
  • aid in detection of brachial plexus injury
65
Q

You are obtaining baseline data from a patient with diabetic peripheral neuropathy. Your PTN SSEPs are unreliable. What efforts should you take to try obtaining reliable data?

A
  • Increase pulse width
  • Decrease the rep rate below 3Hz
  • Stimulate at the pop fossa location
66
Q

The Surgeon requests relaxant be given during your procedure. What effect will paralytics have on your SSEPs?

A

May improve artifact, otherwise no effect

67
Q

During a posterior thoracolumbar fusion, you observe a total loss of bilateral lower extremity SSEP waveforms. tcMEP CMAPs are robust and show no changes. Could a spinal cord injury be present?

A

Yes, with the posterior approach these SSEP changes may represent spinal cord injury, despite the unchanged tcMEP data.

Think about the approach of surgery and what structures are at risk. In this case, a posterior approach puts the dorsal column at most risk. Dorsal column is where the SSEP pathway is located. It is possible to have a partial spinal cord injury, leaving the anterior portion of the cord intact and fully functional.

68
Q

The first synapse in the dorsal column/medial lemniscus pathway takes place where?

A

Medulla

69
Q

A sensory response recorded at 9ms after ulnar nerve stimulation represents

A

A peripheral nerve action potential

70
Q

Increasing number of averages (trials) can help reduce what in the SSEP?

A

Electrical artifact/noise

71
Q
  1. In which type of evoked potential is the scalp position of recording electrodes most critical?
  • Electrocochleogram
  • BAEPs
  • Cognitive evoked potentials
  • Lower extremity SSEPs
A

Lower extremity SSEPs

Think of the homunculus and where lower extremities are located (midline). They have less cortical representation - thus its very important electrode placement is placed correctly.

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