Monitoring Evoked Potentials Flashcards
What is a diminutive human being without any deformity of physiology?
homunculus
Where do the sensory and motor locations reside?
cortex
What is the arrow pointing to?
Label the shaded areas and describe its location relative to the brain.
cerebral longitudinal fissure
Central sulci
Motor area is more frontal than the sensory area.
What does SSEP represent?
somatosensory evoked potential
If want to monitor SSEP for the feet and legs, what electrodes would be used?
C2, C3, and C4
(C = central sulci)
What defines the somatosensory pathway? (2)
Dorsal (posterior) horns = sensory pathway
Ventral (anterior) horns = motor pathway
Which field will generate an impulse first for SSEP? Far or near field?
What do we try to minimize affecting regarding SSEP monitoring?
What could “P” and “N” possibly represent in an SSEP graph?
Far field occurs earlier (Note: Near field would be considered the cortex.)
Latency and increase amplitude of evoked responses
P = positive excursion, N = negative excursion
Monitoring evoked potentials from the ______ will generate an increased amplitude and decreased latency waveform.
arms rather than the legs
There is less resistance from the arms to the head than from the legs to the head.
What nerves are monitored in SSEP? (2)
Left median nerve
Left tibial nerve
Random activity is generated from an evoked response. How is this activity suppressed?
by averaging the potentials
What can anesthetic drugs do to produce a change in sensory and motor evoked potentials?
Can be mistaken for a surgically induced change
What anesthetic drugs do NOT affect SSEPs? (5)
Etomidate
Droperidol
Ketamine
Opiates
Dexmedetomidine
What anesthetic drugs do NOT affect transcranial MEPs? (4)
Etomidate
Ketamine
Opiates
Dexmedetomidine
What anesthetic drugs DO affect transcranial MEPs? (4)
Barbiturates
Diazepam
Midazolam
Volatile agents
What affect do volatile agents have on latency and amplitude?
Dose dependent increase, volatiles have the greatest effect of all drugs.
It causes the greatest increase on latency and greatest decrease in amplitude.
How will N2O affect latency and amplitude?
Increases latency slightly, greater decrease in amplitude
What effect does etomidate have on latency and amplitude?
Increases latency slightly with a pronounced increase in amplitude.
What effect do narcotics have on SSEPs?
MAY increase latency with no effect on amplitude.
Bolus transiently increases latency. Continuous has little effect.
What drug may have been infused to produce the changes in amplitude?
Etomidate which increases amplitude if its puny.
How can you remove ECG interference from SSEPs?
The tachycardia alarm can be fixed by turning on the pacer detect mode.
What is BAEP/BAER/BSER?
What nerve is stimulated?
Brainstem auditory evoked potential/response)
CN 8, auditory
What anesthetics should not be used during BAEPs?
We can use all of them.
What are the guidelines for choosing anesthetics during BAEPs?
IV agents have significantly less effect than “equipotent” doses of inhaled agents
Combinations of drugs produce additive effects
Subcortical (spinal/brainstem) sensory evoked responses are very resistant to effects of anesthetic drugs.
______ responses, because they are entirely cortical suffer the greatest sensitivity to changes in anesthetic drug levels.
VEP (visual evoked potentials)
What spinal horns do motor evoked potentials (MEPs) ellicit?
ventral (anterior) horns
Motor deficits after _______ or _______ may occur without changes in SSEPs.
So, what do you do?
spinal surgery
aortic cross clamping
Motor evoked potentials allow monitoring of pathways not involved in sensory transmission.
What IV agents produce less depression effect on MEPs? (5)
Propofol
Ketamine
Etomidate
Opiates
Dexmedetomidine
What muscles are monitored during MEPs if working around the ear for example?
Orbicularis
Orbicularis oris
What facial nerves are monitored?
Trigeminal (CN V)
Facial (CN VII)
What is the name of the test for neurologic monitoring?
Wake-up test
Monitors of the nervous system can monitor function or adequacy of blood flow, or both. True or false?
True
Most anesthetic drugs have a typical effect on the EEG: small doses produce activation, moderate doses produce slowing with maintenance or increase in amplitude, and large doses produce burst suppression. True or false?
True
EEG changes associated with inadequate CBF are similar to increasing doses of most anesthetic drugs. True or false?
True
Anesthetic effects on cortical SERs are significant and render monitoring difficult. True or false?
True
Subcortical responses (auditory, somatosensory) are resistant to effects of anesthetics. True or false?
True
What may help detect significant risk of stroke at any time during the perioperative period?
transcranial doppler
Cerebral oximetry is a new technology designed to measure the adequacy of CBF. However use of the device remains controversial. True or false?
True, since there is no universal agreement about normal perioperative changes.
