SSEP

Question 1

The patient with a severe PN will likely have preservation of what waveform as opposed to other subcortical waves?

Answer 1

N20

Question 2

What are the different waveforms of the upper extremities?

Answer 2

• EP (Erbs Point) (N9): brachial plexus
• N13: cervical spinal cord
• P14: nucleus cuneatus
• N18: thalamus
• N20: somatosensory cortex

Question 3

What nerves are stimulated in the upper extremities(SSEP)?

Answer 3

Median and Ulnar nerves

Question 4

What are the nerves stimulated in a SSEP of the lower extremities?

Answer 4

Tibial and peroneal nerves

Question 5

Stimulation of the posterior tibial nerve activates the mesial segment of ______?

Answer 5

Posterior paracentral gyrus

Question 6

The lower extremity SSEP tibial stimulation electrodes correspond to what waveforms?

Answer 6

• T12S - IC = LP (N22): cauda equina/lower spinal cord
• Fpz - C5S = P31 and N34: nucleus gracilis and thalamus
• CPz - Fpz = P37: somatosensory cortex
• CPi - Fpz = P37

Question 7

What is the generator for:

EP

Answer 7

Brachial plexus

Question 8

What is the generator for:

N13

Answer 8

Cervical spinal cord

Question 9

What is the generator for:

P14

Answer 9

Nucleus cuneatus

Question 10

What is the generator for:

N13

Answer 10

Cervical cord

Question 11

What is the generator for:

N20

Answer 11

Somatosensory cortex

Question 12

What is the generator for:

PF

Answer 12

Peripheral nerve

Question 13

What is the generator for:

LP

Answer 13

Cauda equina/lower spinal cord

Question 14

What is the generator for:

P31

Answer 14

Nucleus gracilis

Question 15

What is the generator for:

N34

Answer 15

Thalamus

Question 16

What is the generator for:

P37

Answer 16

Somatosensory cortex

Question 17

How are SSEPs most clinically useful?

Answer 17

In detecting abnormalities of joint position, touch, vibration and stereognosis involving the spinal cord, brainstem and cortex

Question 18

Draw out the SSEP sites for Upper and Lower

Answer 18

Upper

• N9: Brachial plexus
• N13: Cervical cord (posterior)
• P14: Nucleus cuneatus (above medulla)
• N18: Thalamus
• N20: Somatosensory cortex

Lower

• N22: Cauda equina
• P31: Nucleus gracillis
• N34: Thalamus
• P37: Somatosensory cortex

Question 19

Where is P22 generated from?

Answer 19

Central or frontal cortex

Question 20

What effect will anesthesia, sleep or sedation have on cortical waveforms (N20, P37/38)?

Answer 20

They will be prolonged or diminished

Question 21

What effect will etomidate have on cortical waveforms?

Answer 21

It will increase amplitude

Question 22

What are the findings of median nerve SSEP in brain death?

Answer 22

• Intact N9 and N13
• Absent P14, N18 and N20
• This pattern could also be seen with a cervicomedullary junction lesion

Question 23

Patient is being evaluated for anoxic brain injury. SSEP at the median nerve shows a normal N20 response. What does this mean?

Answer 23

N20 = somatosensory cortex

This is a hopeful response but does not guarantee a good functional recovery

Conversly, an absent N20 is bad

Question 24

Brain death evaluation. What clinical scenarios can cause an absent N20 besides severe anoxic injury?

Answer 24

Severe bilateral supratentorial lesions

Drug intoxication

Severe cerebral edema (but no clear signs of brain death)