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Volume 1

Evoked Potential Monitoring

QuestionAnswer
What two tracts make up the dorsal lemniscal sensory system? cuneatus and gracilis tracts
Where are the cuneatus and gracilis tracts of the dorsal lemniscal system located? in the posterior (dorsal) cord
What sensations do the cuneatus and gracilis tracts carry? sensations of touch, pressure and vibration
The integrity of the cuneatus and gracilis tracts is assessed by what? somatosensory evoked potentials: SSEP
Touch, pressure, and vibration sensations are carried into the spinal cord vie the __ __. dorsal horn
Touch, pressure, and vibration asend on the ipsilateral or contralateral side? ipsilateral
Where do the sensations of touch, pressure, and vibration cross over? the brain stem
The sensations of touch, pressure and vibration cross over in the brainstem to which two locations? contralateral thalamus and primary sensory cortex
In addition to traveling directly to the primary sensory cortex, sensory information is also transmitted into the __. Reticular activating system (RAS)
In the RAS what happens to sensory information? it percolates upward and spreads throughout the cerebral cortex
The RAS serves as an ___ route by which sensory information reaches the cerebral cortex indirect
The RAS functions to maintain the ____ state. alert/awake
What happens to the RAS when we go to sleep? shuts off
General Anesthethis produce sedation and hypnosis (sleep) by doing what? depressing the RAS
Complete loss of RAS activity is called __. coma
What is the purpose of SSEP monitoring? to evaluate the integrity of the brain or spinal cord during certain types of surdery
What operations are the gracilis and cuneatus tracts of the posterior spinal cord assessed during? spine operations, carotid endardarectomy, aortic surgery, or repair of intracranial aneurysms
What happens if there is posterior cord ischemia or brain ischemia? transmission of action potnetials through the posterior cord and/or brain is diminished, thereby reducing the intensity and delaying the arrival of action potentials reaching the cerebral cortex
What 3 nerves may be stimulated to elicit somatosensory evoked potentials? tibial, median, or ulnar nerves
Somatosensory evoked potentials are recorded from where? the scalp
The sciatic nerve branches into which two nerves? common peroneal nerve and the tibial nerve.
The tibial nerve at the level of the ___ is usually the site of stimulation for somatosensory evoked potential monitoring. ankle
Besides the tibial nerve, which other two nerves may also be stimulated for somatosensory evoked potential monitoring? ulnar or median nerves
The critical electrode for detecting the evoked potential after stimulation of the tibial nerve must be placed over the primary sensory cortex where on the scalp? at the midline of the scalp
If the median nerve or ulnar nerve is stimulated, the critical recording electrodes must be placed over the primary sensory cortex, where on the scalp? somewhat laterally from the midline
For sensory evoked potentials, the stimulating electrodes are placed ___ and the detecting electrodes are placed ____. (Peripherally or Centrally) stimulating- peripherally, detecting- centrally
List the pathway of action potentials from the right tibial nerve to the sensory cortex. right tibial nerve to spinal cord via dorsal horn -> right spinal cord (cuneatus and gracilis tracts) -> lef cerebral cortex -> evoked potential recorded from electrodes between ears near midline (over longitudinal fissure)
After mild electrical stimulation of the nerve occurs, the electrical information reaches the cortex and what occurs? a fluctuation in potential, an evoked potential
What does the early component or early peak of the evoked potential result from? action potentials that are carried via the direct route
What is the direct route? action potentials carried to the primary sensory cortex by the cuneatus and gracilis tracts of the dorsal lemniscal system.
How many neurons compose the dorsal lemniscal system? 3 neurons
What does the delayed or late peak result from? the arrival of action potentials that had traversed the reticular activating system
Where are electrodes located that receive the late peak? anywhere on the scalp
Which peak is larger is magnitude, the early or late peak? late peak
___ and ___ are measured in somatosensory evoked potential monitoring. Latency and amplitude
What is latency? the time it takes for the action potential to traverse the peripheral nerves, spinal cord, and inner brain structures before arriving at the cerebral cortex
What is amplitude? the magnitude or size of the evoked potential
What is somatosensory monitoring used to detect? dorsal spinal cord and brain ischemia
The waves that deflect downward are designated ____ and those that deflect upward ___. downward- P: positive; upward N: negative
The latency in milliseconds is indicated by the numbers placed where? after the P or N
An (increase/decrease) in amplitude during evoked potential monitoring suggests that damage is occurring in the neural pathway being monitored. decrease
An (increase/decrease) in latency during evoked potential monitoring suggests that damage is occurring in the neural pathway being monitored. increase
Which nerves are stimulated during spinal scoliosis surgery? tibial
What does increased latency and decreased amplitude of the SSEP with spinal scoliosis surgery indicate? ischemia of the posterior spinal cord
In thoracic and thoracolumbar aortic reconstruction, ____ is one major concern. spinal cord ischemia
During thoracolumbar aortic reconstruction, because ischemia of distal nerves, including posterior tibial nerves, alters conduction and the SSEP, spinal stimulation via a __ ___ electrode may be used. lumbar epidural
Increased latency or decreased amplitude during thoracolumbar surgery indicates what? ischemia of the posterior cord
The incidence of paraplegia following repair of thoracic or thoracolumbar aortic aneurysms varies from __-__%. 5-40%
Since SSEP monitoring assesses the integrity of the __ cord only, monitoring of the __ cord is useful. (Anterior/posterior) posterior, anterior
__ ___ potentials are used to monitor iscemia of the anterior (ventral) columns. motor evoked
What is the most commonly used technique for motor evoked potentials? Stimulation over the __ __ or ___ __ with sensing over the ___ ___. motor cortex or cervical spine; popliteal nerve
The motor cortex or cervical spine is ____ and popliteal nerve is ___. (central/peripheral) central, peripheral
In a carotid endardarterectomy, which nerves are stimulated? median nerves
What do increased latency and decreased amplitude indicated during SSEP of a carotid endarterectomy? ischemia of deep brain structures and the sensory cortex
Why is the usefulness of somatosensory evoked potential monitoring during carotid endarterectomy questionable? poor outcome changes in SSEP have been noted
Somatosensory evoked potentials can be modified by changes in what parameters? temperature, systemic blood pressure, paCO2, PaO2
SSEP are elicited by repetitive stimulation of what 3 nerves? tibial, median, or ulnar nerves
SSEP is useful for monitoring function of ___ or __ during surgery. dorsal spinal cord or brain
What surgeries is SSEP useful for monitoring? spinal cord surgery, endarterectomy, aortic surgery, or during repair of intracranial aneurysms
Brainstem Auditory Evoked Potentials are elicited by __ ___. auditory clicks
BAEP re useful during operations involving CN ___. CN VIII
Visual evoked potentials are elicited by what? flashes of light
When are visual evoked potentials useful? if surgery is near the optic nerve
Give an example of a surgery that may use visual evoked potentials. trans-sphenoidal approach to anterior pituitary tumor
Visual evoked potentials monitor the integrity of the __ nerve, CN __. optic nerve, CN II
GEneral intravenous anesthetics and volatile inhaltional agents have what effect on evoked potentials? increase the latency and decrease the amplitude
Rank visual, SSEP, and BAEP and their sensitivity to anesthetics. VEP most, SSEP intermediate, BAEP least
How do you remember which is most sensitive? a VEP: V for Very sensitive; SSEP: S for somewhat sensitive; BAEP: B for Barely sensitive
Somatosensory evoked potentials are recorded from electrodes placed over the ___ ___ if the tibial nerve is stimulated bilaterally. longitudinal sulcus
If during a Harrington Rod procedure the amplitude of the SSEP decreases the latency increases, damage to what region of the spinal cord (anterior, posterior, lateral) may have occurred? The posterior cord may have incurred damage
Created by: valleyanesthesia