A is for Amplitude - ISETT- Chapter of ASET

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Transcript A is for Amplitude - ISETT- Chapter of ASET

Quick EEG facts
• Physicians use the EEG to aid in the
diagnosis of : epilepsy, cerebral tumors,
encephalitis, and stroke
• EEG usage was first documented by Hans
Berger in 1924.
• Berger was the first to define band width
frequencies by applying electrodes to the
forehead and occiput.
A
is for Amplitude
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How big the waveform is..
Amplitude of pediatric EEG may be
substantially highter that that of an adult.
Measured in Millimeters
Can be converted to voltage by taking the
amplitude x sensitivity.
AMPLITUDE = VOLTAGE
SENSITIVITY
B
IS FOR BACKROUND
Characteristics of pediatric EEG
(0-12 months of age)
• Posterior dominate rhythm established at
3-4 Hz at 3 months of age.
• Posterior dominate rhythm of at least 4 Hz
at 6 months of age.
• Posterior dominate rhythm of at least 6 Hz
by 12 months of age
• Sleep stages can consist of active sleep
as well as quiet sleep
C
is for
Calibration
• Sending a know square wave signal into
each amplifier
• Should be performed at the beginning of
every study (20 seconds).
• Tests the amplifiers, machine settings,
filters settings
D IS FOR DROWSINESS
Drowsiness (Stage 1 sleep)
• Slow rolling eye movements
• Background activity becomes slower, less
prominate, and fragmented.
• Presents of Positive occipital sharp
transients of sleep (POSTS), as well as
Vertex sharp waves.
• Hypnagogic Hypersynchrony
(in ages 3-13)
Drowsiness in Adult EEG
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Pt is a 7 y/o male being evaluated for 1 T/C seizure
episode lasting 10 seconds occurring 2 days ago.
Awake/Sleep eeg ordered.
Delta Brush
D
is for duration
• Defined a width of the waveform
• Expressed in seconds or milliseconds
For an analog recording, you would measure the
width of the waveform in millimeters, and divide
by the paperspeed.
Example: if you wanted to know the duration of a
waveform measuring 4mm in width, you would
simply divide 4mm by known paperspeed
i.e…30mm/sec.
4/30=.133 seconds
or 133 msec
D
continued…..
• For a digital recording, you will measure
the width of one second on the record, and
use it as your paperspeed
Example: If 7mm is the width of your
waveform, and one second of your digital
recording measure our to be 28mm.
Then 7/28=.250 seconds or 250msec
D
is also for
documentation
• Always document: Time when the pt is at
maximum level of alertness, any changes
in level of consciousness, eye
opening/closing, any type of activation or
stimulation that is attempted, all pt
activities or movements ( especially if it is
indicative of a seizure ), impedances, filter
settings and parameters.
E
is for eye
polarity
• The cornea of the eye is electropositive in
relation to the retina.
• Eye blinking artifact is a common fixture of most
normal EEGs.
• When blinking, the eye lid closes, while the eye
ball turns in an upward direction. This causes
the frontopolar electrodes to become more
electropositive in respect to the electrodes that
they are referred to. The end result a transient
upward or downward deflection depending on
the electrode derivation and direction of eye
movement.
E
is also for end of
chain!
• When the last electrode derivation in a
series of a specific montage shows a
potential of highest amplitude (referential),
or a possible phase reversal (bipolar).
• Remedied by adding another electrode to
the series, or selecting an alternate
montage that transcends the focus in
question.
F
is for frequency
• Refers to the speed of EEG activity within
one second of recording.
• Can be identified in Hertz (Hz) or Cycles
per second (CPS).
• Classified as bandwidth: 1-3 Hz Delta
4-7 Hz Theta
8-12 Hz Alpha
13-…Hz Beta