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

• 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

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

B IS FOR BACKROUND

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

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)

D IS FOR DROWSINESS

Drowsiness in Adult EEG

Stage I. The earliest indication of transition from wakefulness to stage I sleep (drowsiness) is shown hereand usually consists of a combination of 1) drop out of alpha activity and 2) slow rolling eye movements.

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