Somatosensory evoked potentials (SSEP)

1. What is the pathway of SSEPs?
2. How is the SSEP initiated and recorded?
3. What is SSEP used for?
4. How is SSEP used during spinal surgery?
5. What are the advantages and disadvantages of SSEP?

Answers:
1. The afferent potential travels from the peripheral nerve to the plexus, root, spinal cord (post column), contralateral medial lemniscus, thalamus, to the somatosensory cortex.
2. SSEPs are initiated by repetitive submaximal stimulation of a sensory nerve, mixed nerve, or dermatome. It is recorded from the spine or scalp.
3. SSEP is used to monitor peripheral nerve injuries, CNS lesions (multiple sclerosis), or intra-operative monitoring during a spinal surgery.
4. During spinal surgery, the loss of tibial nerve potentials with preservation of the median nerve indicates an injury.
5. The advantage is that abnormal results occur immediately. Disadvantages include: only evaluates nerve fibers sensing vibration and proprioception, focal lesions can be diluted, adversely affected by sleep and high dose general anesthesia.