Guide
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BrainZ Classification Guide
The Classification Guide The BrainZ Classification Guide is designed to assist users in identifying abnormal neurological events and artifacts by providing sample traces with explanations and possible interpretations. Diagnosis of patient condition should only be made by qualified medical professionals in conjunction with traditional neurological assessment and other clinical information.
Glossary
Term or Abbreviation
aEEG (Amplitude-integrated EEG)
Meaning
- A time-compression technique for presenting long EEG recordings, using an asymmetrical filter, rectifier, peak detector
and semi-logarithmic amplifier. Amplitude
- A measurement of the level of brain activity detected as an electrical signal, measured in microvolts (μV) peak-to-peak.
Artifact
- Any electrical signal detected by an EEG machine from an extra-cerebral source (for example, electrode or cable
movement, AC supply noise, ventilator noise). Electrode
- Conductor applied over, or inserted into, a region of the scalp to detect electrical activity of the brain.
EEG (Electroencephalograph)
- Medical electrical equipment intended for production of graphic recordings and/or a visual display of electrical activity of
the brain. EMG Artifact
- Artificial signal caused by the electrical activity of muscles.
Frequency
- The number of complete cycles of repetitive waves or complexes in one second, measured in Hertz (Hz).
Impedance
- The opposition to the flow of an electric current through a conductor giving a measurement of the quality of contact
between electrode and scalp. Intensity
- A measurement of the electrical energy present in the frequency band of interest.
Seizure pattern
- A phenomenon consisting of repetitive EEG discharges characteristic pattern of evolution, lasting at least ten seconds.
The waves are generally rhythmic, sharp or spike waveform.
Sample Traces www.brainz.com
Sample traces may assist users in identifying abnormal neurological events and artifacts, by providing explanations and possible interpretations. Note: The sample traces are all taken from term infants. Some EEG indications that are abnormal for term infants may be normal for pre-term infants. The sample traces provided are categorized into different groups: Continuous Normal Voltage
page 5
Discontinuous
page 6
Burst Suppression
pages 7 / 8
Continuous Low Voltage
page 9
Isoelectric / Flat Trace
page 10
Unilateral Cerebral Injury
page 11
Seizures
page 12
Repeated Seizures
page 13
Continuous Seizures
page 14
ECG Artifact
page 15
Movement Artifact
page 16
High Frequency Ventilator Artifact
page 17
EMG Artifact
page 18
aEEG Amplitude Values This classification guide uses principles for interpreting aEEG based on information derived from numerous clinical studies*. Many of these studies include criteria based on specific amplitude values. The standard values used in these studies are: Normal Lower margin > 5 µv Upper margin > 10 µv
Burst suppression Lower margin < 5 µv Intermixed with bursts > 10 µv
Discontinuous Lower margin < 5 µv Upper margin > 10 µv
Continuous Low Voltage Lower margin < 5 µv Upper margin < 10 µv
However, it is important to note that amplitude values should not be used in isolation. This information should be used in conjunction with traditional neurological assessment and other clinical information. * For further reference information and published clinical data please refer to the BrainZ Bibliography.
aEEG
EEG Waveform
Continuous Normal Voltage
• Continuous EEG trace with good variability and no repetitive waveforms (especially sharp/ spike waves). • Reactive to stimuli. • Twenty minute periods (typically) of alternating wide and narrow trace width, normal amplitude. • Wakefulness or active sleep is represented by a narrowing of the aEEG, quiet sleep by widened trace.
Continuous Normal Voltage
Discontinuous
EEG Waveform
• Periods of lower amplitude interspersed with periods of higher amplitude on raw EEG trace.
aEEG
www.brainz.com
• Wide depressed aEEG trace with variability in lower margin.
Comments: Can be indicative of cerebral injury, anti-convulsant therapy or prematurity.
EEG Waveform
• Periods of abnormally high amplitude activity (bursts) lasting 1 to 3 seconds, separated by prolonged periods of markedly suppressed amplitude.
aEEG
Burst Suppression (Short Inter-burst Interval)
• Flat lower aEEG margin. The spikes in the upper aEEG margin represent the bursts, therefore the space between the spikes indicates the length of suppression.
Comments: Prolonged severely abnormal traces (burst suppression and continuous low voltage) indicates a high probability of severe brain injury. Burst Discontinuous Suppression
Burst Suppression (Long Inter-burst Interval)
EEG Waveform
• Periods of abnormally high amplitude activity (bursts) lasting 1 to 3 seconds, separated by prolonged periods of markedly suppressed amplitude.
aEEG
www.brainz.com
• Flat lower aEEG margin. The spikes in the upper aEEG margin represent the bursts, therefore the space between the spikes indicates the length of suppression.
Comments: Prolonged severely abnormal traces (burst suppression and continuous low voltage) indicates a high probability of severe brain injury.
aEEG
EEG Waveform
Continuous Low Voltage
• Continuous low amplitude.
• Narrow aEEG trace with greatly lowered upper and lower margins.
Comments: Prolonged severely abnormal traces (burst suppression and continuous low voltage) indicates a high probability of severe brain injury. Continuous Low Voltage
Burst Suppression
Isoelectric / Flat Trace
aEEG
EEG Waveform
www.brainz.com
• Very low amplitude (inactive).
• Low amplitude, narrow trace (may have low amplitude spikes).
Comments: Prolonged severely abnormal traces (burst suppression and continuous low voltage) indicates a high probability of severe brain injury.
10
EEG Waveform
• Differing amplitude and variability between left and right hemispheres.
aEEG
Unilateral Cerebral Injury
• Depressed upper / lower margins on injured hemisphere.
Comments: Unilateral injury may be caused by cerebral infarction, asymmetrical cerebral ischaemia or intracerebral haemorrhage.
Unilateral Cerebral Injury
Isoelectric / Flat Trace
11
Seizures
aEEG
EEG Waveform
www.brainz.com
• Repeated spike / sharp waveforms lasting longer than 10 seconds.
• Distinctive rise in the lower (and often upper) margin.
Comments: Some forms of artifact may cause a similar rise in the lower margin of the aEEG trace, but the corresponding EEG Waveform trace will lack the repetitive character of a seizure.
12
EEG Waveform
• Repeated spike / sharp waveforms lasting longer than 10 seconds.
aEEG
Repeated Seizures
• Distinctive rise in the lower (and often upper) margin.
Repeated Seizures
Seizures
13
Continuous Seizures
EEG Waveform
• Continuously repetitive spike / sharp waveforms on the raw EEG trace.
aEEG
www.brainz.com
• Characteristic “saw-tooth” pattern.
Comments: Status epilepticus. 14
EEG Waveform
• Low level repetitive spikes correlated with heartbeat.
aEEG
ECG Artifact
• ECG interference is not visible in the aEEG trace. Comments: This artifact is generally only problematic in extremely low amplitude traces viewed on the EEG Waveform display, particularly if the vertical sensitivity has been increased (may be incorrectly interpreted as low voltage seizure activity).
ECG Artifact
Continuous Seizures
15
Movement Artifact
aEEG
EEG Waveform
www.brainz.com
• High amplitude, low frequency non-repetitive EEG waveforms correlating with movement. • Slight or moderate rise in the aEEG (particularly the lower margin) if movement is prolonged.
Comments: Indicative of movement of the infant, leads or sensors. Movement may produce high voltage spikes similar to those of seizure patterns, but lacking the repetitive character of seizures.
16
EEG Waveform
• Low amplitude spikes correlating with ventilator frequency.
aEEG
High Frequency Ventilator Artifact
• Lower margin of aEEG trace may be raised by ventilator signal.
Comments: Exercise care in interpreting the aEEG trace when HFV artifact is present, as rise in aEEG lower margin may be incorrectly interpreted as seizure activity or normal. HF Ventilator Artifact
Movement Artifact
17
EMG Artifact
EEG Waveform
• Fast, spikey “fuzz” on top of EEG waveform.
aEEG
www.brainz.com
• Lower margin of aEEG trace is raised by artifact.
Comments: Exercise care in interpreting the aEEG trace when EMG artifact is present, as rise in aEEG lower margin may be incorrectly interpreted as seizure activity or normal. 18
Subject : BrainZ Classification Guide Part No : CZV00071 Version : 1 Issued : 08/2007 © 2007 BrainZ Instruments Ltd
For contact details refer to :
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