Indications for EEG monitoring

• Seizure detection

• Characterization of clinical events

• Encephalopathy evaluation 

• Prognostication of outcome

• Medication titration (e.g. pentobarbital for ICP management)

• Evaluation of brain death 

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Risks and Limitations

Risks

• Primary: scalp abrasions

• Secondary: potential adverse effects from medications administered due to EEG findings

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Limitations

• Cost and resources

• Frequently nonspecific –best used in conjunction with other modalities of neurological evaluation

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Orientation to EEG

• F- Frontal

• P- Parietal

• T- Temporal

• C-Central

• O-Occipital

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• Odd numbers are left

• Even number are right

• Each column represents 1 sec

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Orientation to EEG Interpretation

• Frequency- number of times a repetitive wave recurs in 1 sec

• Delta (1-3 Hz), Theta (4-7 Hz), Alpha (8-13 HZ), Beta (>13 Hz)

• Amplitude- vertical distance of a wave in microvolts

• Waveform- shape of the wave

  • Sharp  (70-200ms)

  • Spike (20-70 ms)

  • Spike and wave complexes (spike followed by a slow wave)

• Continuity

  • Nearly continuous : <10% attenuation < 10 uV

  • Discontinuous:  10-50% with periods of attenuation < 10 uV

  • Suppression-burst : discontinuous with interburst interval amplitude <10 uV > 50% of the time

  • Suppression : all activity <10 uV

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• Descriptors of periodicity and rhythmicity

  • Periodic Discharges (PD)

  • Rhythmic Delta Activity (RDA)

  • Spike-Wave (SW; includes sharp-wave)

• Seizure definitions

  • Electrographic Seizure - paroxysmal EEG change with or without associated clinical change

    • Abnormal activity- sudden, repetitive, evolving, and stereotyped. amplitude at least 2µV p-p

    • Minimum duration 10 secs and ≥10secs between

  • Clinical Seizure - paroxysmal clinical change

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• Electroclinical Seizure - seizure with both EEG and clinical manifestation

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• Status Epilepticus (SE)

  • Continuous seizure for ≥ 5 minutes or recurrent for > 5 minutes without return to baseline MS

  • Neonates SE - recurrent seizures for ≥50% of 1hour EEG epoch

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Continuous EEG Monitoring

• High rate of electrographic only seizures (7-30% of patients in PICU, CICU and NICU)

• After seizure treatment 58% of neonates have only electrographic szs

• Several studies consistently report majority of seizures are noted in the 1st 24 hours of monitoring

• Consider monitoring for additional 24 hours after the last seizure

• Benefits of seizure identification

  • Seizures are the symptom of a CNS insult

  • Seizures can be associated with secondary injury (increased sz burden inversely associated with functional outcome)

  • Early identification and treatment may improve outcome

  • 25% of infants thought to have seizures have no seizures on EEG

  • 44-70% of behaviors thought to be seizures have no EEG correlate 

    • Seizure mimics

      • Clonus, jittery

      • Benign neonatal sleep myoclonus

      • Hyperekplexia (stiff when awake, startle)

      • Dystonic posturing

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Electrographic Seizures

• Electrographic seizures (ES) are associated with

  • worse outcome in PICU patients with no prior neurological dx 

  • unfavorable outcome in comatose PICU/NICU patients 

• Greater decline of PCPC with higher seizure burden 

  • 67% have decline if maximal seizure burden 15% per hour

  • No decline if seizures 1.8% per hour

  • Greatest decline if 20%/hour (12 min)

  • Odds of decline increase 1.13 for every 1%  increase in maximum hourly seizure burden

 

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