SSEP Flashcards
The patient with a severe PN will likely have preservation of what waveform as opposed to other subcortical waves?
N20
What are the different waveforms of the upper extremities?
- EP (Erbs Point) (N9): brachial plexus
- N13: cervical spinal cord
- P14: nucleus cuneatus
- N18: thalamus
- N20: somatosensory cortex
What nerves are stimulated in the upper extremities(SSEP)?
Median and Ulnar nerves
What are the nerves stimulated in a SSEP of the lower extremities?
Tibial and peroneal nerves
Stimulation of the posterior tibial nerve activates the mesial segment of ______?
Posterior paracentral gyrus
The lower extremity SSEP tibial stimulation electrodes correspond to what waveforms?
- 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
What is the generator for:
EP
Brachial plexus
What is the generator for:
N13
Cervical spinal cord
What is the generator for:
P14
Nucleus cuneatus
What is the generator for:
N13
Cervical cord
What is the generator for:
N20
Somatosensory cortex
What is the generator for:
PF
Peripheral nerve
What is the generator for:
LP
Cauda equina/lower spinal cord
What is the generator for:
P31
Nucleus gracilis
What is the generator for:
N34
Thalamus
What is the generator for:
P37
Somatosensory cortex
How are SSEPs most clinically useful?
In detecting abnormalities of joint position, touch, vibration and stereognosis involving the spinal cord, brainstem and cortex
Draw out the SSEP sites for Upper and Lower
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
Where is P22 generated from?
Central or frontal cortex
What effect will anesthesia, sleep or sedation have on cortical waveforms (N20, P37/38)?
They will be prolonged or diminished
What effect will etomidate have on cortical waveforms?
It will increase amplitude
What are the findings of median nerve SSEP in brain death?
- Intact N9 and N13
- Absent P14, N18 and N20
- This pattern could also be seen with a cervicomedullary junction lesion
Patient is being evaluated for anoxic brain injury. SSEP at the median nerve shows a normal N20 response. What does this mean?
N20 = somatosensory cortex
This is a hopeful response but does not guarantee a good functional recovery
Conversly, an absent N20 is bad
Brain death evaluation. What clinical scenarios can cause an absent N20 besides severe anoxic injury?
Severe bilateral supratentorial lesions
Drug intoxication
Severe cerebral edema (but no clear signs of brain death)
