Evoked Potential

CNIM - Certificate Neurophysiologic Intraoperative Monitoring

Terminology

  • ankylosis
  • andylosing spondylities
  • aphasia
  • apraxia
  • ataxia
  • claudication
  • dyskinesia
  • far-field
  • lordosis
  • kyphosis
  • myelopathy
  • near-field
  • paresthesia
  • osteoarthritis
    _
  • osteopathy
  • osteoma
  • osteomyelitis
  • osteopathy
  • osteophyte
  • osteoporosis
  • osteosarcoma
  • pseuodoarthrosis
  • radiculopathy
  • rheumatoid arthritis
  • scoliosis
  • spinabifida
  • spinal stenosis
  • spondylolisthesis
  • spondylolysis
  • spondylosis
  • subluxation
  • radiculopathy

Auditory Terminology

  • acoustic neuroma
*from handwritten notes at chucks house*
dB = 20 log E1/E2; the voltage ratio (six zeroes = 120)
common mode rejection ratio
waveform polarity and polarity of the amplifier inputs
polarity convention of amplifier inputs
default convention is negative up; wave 1 of BAEP
square root of the number of trials averaged; square root of 100 responses equals ten
avoid signals that are a multiple of 60Hz; 60 cycles per second will interfere
SSEP's at a range where time is a factor; say stimulator is at 4 times per second and 2 minutes is a practical setting (120 secs = 500 trials)
2 or 300 is better; I've seen some people get excellent SSEP's at 50 trials, initally set for 200
stimulation time and intensity
extra ocular muscles
vagus monitoring and vocal chords
what is the effect of mis-positioning electrode position? a small change makes a big change in the potential; electrode position is extremely critical
N20 near field cortical medial ulnar
N34 response at the medulla; subcortical somatosensory response to tibial stimulation
far field and near field
major potentials - N20 - primary cortical response
P40 or P37 - primary cortical response to tibial stimulation
6 ms earlier P31, P34 are subcortical potentials
Amplifiers; gain - how many times the amplifier
high pass filter - passes high and blocks low; place capacitor
low pass filters - place inductor
capacitance - passes AC blocks DC
Inductance - Passes DC blocks AC
resistance - passes AC, passes DC
Impedance is a function of frequency
can clean up by bringing high pass filter
Band pass filters - 50-300 for SSEP's
  • passes dominant frequencies
  • eliminate frequencies outs of that
  • improve signal to noise ratio
A practical approach to neurophysiologic intraoperative monitoring; editor Aalif M. Husain
electrodes - more voltage to the same current
Dwaves - subdural
referential recording - as opposite
bipolar recording
C3 - CZ - left posterior for right hemisphere; electrode placement; dendritic axons
ground is to minimize stimulus artifact between stimulation and recording sites; you want it to be closer to the stimulation site
T5 Spine afferent voltage at the popliteal fossa
the higher the resistance the less the current which equals a poorer signal
important that they're balanced because common mode rejection - balanced and low
surface electrodes; paste; subcutaneous are more reliable
nyquist theorem
highest frequency for EEG is 70 so need  to measured at 140
human hearing is 20-20,000 Hz so for, sampling is 441 = obeys nyquist @ 2x
safe levels for EMG; signal of interest overlaps, distribution to EKG
ABR - already decreases example
SEP 3-10ms
MEP 50-1000hz
EEG slow D wave more than 1 second
EMG compound muscle action potentials
all signals are constantly present
to avoid aliasing, sample at or above the nyquist and aliasing
what determines max frequency constant
get rid of frequencies before analog to digital conversion
ACNS guidelines

monitoring for position, for spinal cord SEPs and EMGs
4 extremities for control and to monitor and test if upper extremities connection are not lost

younger people the spinal cord is lower; higher in older people unless it's tethered
possible correlation with the actual height and individual differences

what is at risk???
  • patient positioning
  • upper extremities
  • lower extremities
laminectomy to get tumor, will open up dura; do not run motors in this case and warn of EMG, will likely use stimulation to map ends of tumor; listen to the surgeon

Dwaves are cortical; this is the action potential traveling down the spinal cord; they are not able to be lateralized
  • ball tip stimulator
  • close to the ???
  • stimulates across from left to right
antidromic - stimulating normally
orthodromic - stimulating backward
record directly from muscle

Bowel & Bladder function is most important to be able to walk and go to the bathroom

Healthy stimulation is at 0.5 mA (milliamps) *Chuck uses 1mA at some arbitrary cutoff
Looking for amplitude changes between rostral and caudal Dwave electrodes

Myotome

Remember it's the difference in potential between active and reference also the first is a negative/upward deflection

gain output/input x amp max sensitivity is small number 10 microvolt is fine for?????

*the latency is efferent for upper and lower extremities
no notch filter because it's right at the frequencey we're looking for, essentially a huge valley right at where the mark is
recruiting
for EMG activity you go from 1000 high cut to 70 for the EMG
biggest MEP is about 1000 microvolts or even 5000 microvolt

so 50 microvolt for lower extremities is good because these are smaller potentials
  • but you can use 100 microvolt for the hands because these can get high activity
separate tests for things i'm only going to use at separate times during the case

Papers mentioned in CNIM Packet

Guideline 1: Minimum Technical Requirements
Guideline 2: Pediatric Cases
Guideline 3: Cerebral Death
Guideline 4: Standards of Practice in clinical electroencephalography
Guideline 5: Standard Electrode Position
Guideline 6: A Proposal for EEG Montage
Guideline 7: Guidelines for writing reports
Guideline 8: Recording EEG on digital media
Guideline 9A: Guidelines on Evoked Potentials
Guideline 10: Guidelines for writing clinical evoked potential reports
Guideline 11A: RECOMMENDED STANDARDS FOR NEUROPHYSIOLOGIC INTRAOPERATIVE MONITORING –PRINCIPLES
Guideline 15: Intraoperative monitoring with somatosensory and transcranial electric motor evoked potentials

AORN "Standards, Recommended Practices, and Guidelines
ASET Performance Issues
Surgery of the Cranial Nerves at the Posterior Fossa
Chiappa Evoked Potentials in Clinical Medicine 1997
Eversole Current Practice of Clinical Electroencephalography
Up and Down the Spinal Cord
A Practical Approach to Neurophysiologic Intraoperative Monitoring
Isley Balzer Intraoperative Motor Evoked Potentials American Journal of Electroneurodiagnostic Technology
Joint Commission on Accreditation for Healthcare Organizations National Patient Safety Goals www.jointcommision.org
Handbook of Spinal Cord Monitoring; Proceedings of the Fifth International Symposium on Spinal Cord Monitoring
Kartush Neuromonitoring in Otology and Head and Neck Surgery 0881678465
Atlas of Electromyography
Spehlman's Evoked Potential Primer
Intraoperative Neurophysiologic Monitoring, 2nd Edition Aage Moller
Intraoperative Monitoring of Neural Function: Handbook of Clinical Neurophysiology
Alexander's Care of the Patient in Surgery
Primer of Intraoperative Neurophysiologic Monitoring
Intraoperative Neurophysiologic: A Comprehensive Guide to Monitoring and Mapping
Handbook of EEG Interpretation
Tyner Fundamentals of EEG technology vol 1: Basic Concepts and Methods
Wilson-Pauwels Cranial Nerves in Health and Disease 2nd Edition
Yamada Practical Guide for Clinical Neurophysiologic Testing
Zourdakis A Concise Guide to Intraoperative Monitoring
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