Neurological Monitoring
© D. J. McMahon 2014
rev 141122, 2015-11-24
Neurological Monitoring
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Electroencephalography (EEG)
EEG Compressed Spectral Array (CSA)
Bispectral Index (BiS)
Evoked Potentials
Electronystagmography (ENG)
Medtronic’s Nerve Integrity Monitor (NIM series)
Functional Magnetic Resonance Imaging (fMRI)
1:
Electroencephalography
(EEG)
3-D interactive graphic of brain function:
http://outreach.mcb.harvard.edu/animations/brainanatomy.swf
The Twelve Cranial Nerves
The Twelve Cranial Nerves:
I
Olfactory Nerve
II Optic Nerve
Smell
Vision
III Oculomotor Nerve Eye movement; pupil constriction
IV Trochlear Nerve
Eye movement
V Trigeminal Nerve
Touch & pain in face and head; mastication
VI Abducens Nerve
Eye movement
The Twelve Cranial Nerves, cont’d:
VII Facial Nerve
Taste (front of tongue); ear;
muscles in facial expression.
VIII Vestibulocochlear Nerve Hearing; balance
IX
Glossopharyngeal Nerve Taste (back of tongue); tonsil, pharynx;
some muscles used in swallowing.
X
Vagus Nerve
Sensory, motor and autonomic functions of
viscera (glands, digestion, heart rate)
XI
Spinal Accessory Nerve
Controls muscles used in head movement.
XII Hypoglossal Nerve
Controls muscles of tongue
The Glascow Coma Scale
For assessing level of consciousness in patients with
brain disease, head trauma, etc.
Range: 3 - 15.
The first human EEG recording,
obtained by Hans Berger in 1924.
The upper tracing is EEG, and the lower is a 10 Hz timing signal.
EEG Recording Parameters:
per American Clinical Neurophysiology Society, 2008
Standard sensitivity:
7uV / mm
Sensitivity Range:
5 – 10 uV / mm
Calibration reference: 50uV
Hi and Lo filters:
< 1Hz and >70Hz
Paper speed:
30 mm / s
Digital speed:
10 sec / page
Minimum time:
20 minutes
Instrumentation Amp:
Differential amplifier specifically designed for use in
measurement and test equipment.
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very low DC offset
low drift
low noise
very high gain
very high common mode rejection ratio (CMMR)
very high input impedance
Can be discrete components, or an IC
Common Mode Rejection Ratio
(CMRR)
The measure of the capability of an instrument to reject a signal that is
common to both input leads.
The CMRR is defined as the ratio of the powers of the differential gain over
the common-mode gain, measured in positive decibels (thus using the 20
log rule):
CMRR = 20 log
EEG Parameters:
(per Chatterjee)
Frequency range: 0.5Hz - 100Hz
Amplitude:
10 - 200 μV
Divided into four sub-ranges:
Delta:
0.5 to 3 Hz
Theta:
4 to 7 Hz
Alpha:
8 to 13 Hz
Beta:
14 to 30 Hz
Delta Waves
> < 3 Hz
> Highest amplitude
> Normal and deep sleep
Theta Waves
> 4 to 7 Hz
> Detected in parietal-temporal zones
> Normal in deep sleep
Alpha Waves
> 8 to13 Hz
> 10 to 50 mV amplitude
> Dominate when in the relaxed patient,
eyes closed. Abolished during sleep.
Beta Waves
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14 to 30 Hz
Detected in frontal-parietal zones
Low amplitude
Dominant in patients when alert & aware
Gamma Waves
> 30 to 100 Hz ?
> Evident in some cognitive (thinking)
or motor activity
> Detected during meditation
International “10-20”
Electrode Placement:
International 10-20
Electrode Placement:
Unipolar mode
Averaging mode
Bipolar mode
www.youtube.com/watch?v=nRTT88B2uOA
Typical EEG recording:
Abnormals
Epileptic event
Epileptic event
Sources of artifact in EEG recording:
> Physiological interference –
- cardiac
- adjacent muscles of the head
- high scalp impedance
> Electrode issues –
- bad positioning
- poor contact
- sweat
> Electromagnetic interference –
- 60 Hz line frequency
- adjacent devices (ESUs, pacemakers, etc)
EEG simulator for
performance checks:
Netech model330
EEG Outputs
Five separate floating outputs
E1+, E2+, E3+, E4+, E5+
and
E1-, E2-, E3-, E4-, and E5-.
Two reference outputs marked Ref
Waveforms:
Frequency: 1 kHz
Amplitude: 0.64 microVolt
Sine, Square, and Triangle:
Frequencies: 0.1, 0.5, 2, 50, and 60 Hz.
Amplitude: 10, 30, 50, 100, 500 microVolt,
1, 2, and 2.5 milliVolt
EEG simulator for
performance checks:
Grass ‘EEGsim’
> 32 channels
> EPROMs for normal and abnormal simulations
2:
EEG Compressed Spectral Array
(CSA)
> Processes raw EEG signal in terms of
power in frequency domains, then displays
the result as frequency vs time.
> Very useful to assess the effect of
medications, or the depth of anesthesia.
Power vs Frequency in EEG
Four steps of Compressed Spectral Analysis:
see next slide…
Display of a Compressed Spectral Analysis signal:
Typical display of Compressed Spectral Array
Bilateral CSA display showing
difference between hemispheres
3:
Bispectral Index (BiS)
Monitors EEG with minimal electrode
inputs, processes the EEG and creates a
numerical value that indicates the
level of awareness.
Especially useful for patients under
general anesthesia or
seriously impaired patients in the ICU.
EEG at various
levels of
anesthesia
BiS values at
various levels of
awareness
Aspect Medical’s
‘Vista’ BiS monitor:
2- or 4-channels
http://www.aspectmedical.com/products
Aspect Medical’s
BiS module,
and engine,
for Philips systems
in anesthesia or
in critical care unit
4:
Evoked Potentials:
Monitoring of the neurologic
response to a stimulus.
-- Visual evoked response
-- Auditory evoked response
-- Somatosensory evoked response (SSEP)
- stimulus: 50 – 1000 s, 0-100 mA
- often applied at tibia and wrist
Stimulus point
Neurological testing station
Neurological testing station
Infra-Red light source & camera
5:
Electronystagmography
(ENG)
nystagmus = abnormal vertical or
horizontal oscillations of the eye
ENG studies diagnose disease states
of the inner ear or brain
http://www.youtube.com/watch?v=phpe_RVGqcA
Nystagmus:
"Optokinetic nystagmus" by Student BSMU at the English
language Wikipedia. Licensed under CC BY-SA
6:
Medtronic’s “NIM” series –
> Nerve Integrity Monitor, used to
assure that major nerves are not
injured during nearby surgical
procedures of the head & neck
NIM-Response 3.0:
NIM-Response 2.0:
Major Players in
Electroencephalography
and Related Diagnostics:
Nihon-Kohden
Grass
Nicolet
Medtronic-Xomed
Aspect Medical
Functional Magnetic Resonance Imaging
(fMRI)
• functional MRI (fMRI) is a functional neuroimaging procedure using
MRI technology that measures brain activity by detecting changes
associated with blood flow. This technique relies on the fact that
cerebral blood flow and neuronal activation are coupled. When an
area of the brain is in use, blood flow to that region also increases.
from: Wikipedia
Lab of Stanford psychology Associate Professor Brian Knutson, who studies
reward processing in a small area of the brain known as the nucleus
accumbens. Precisely how that structure activates is at the heart of an
ongoing debate about reward circuits – a subject that holds relevance for our
understanding of everything from addiction to financial risk-taking.