Electro-Encephalogram (Eeg)

Electro-Encephalogram (Eeg)


EEG (Berger’s rhythm) 

Types of Rhythms (Important in Sleep-Wake Cycle) – Bilaterally Symmetrical

  • Alpha
  • Beta
  • Theta
  • Delta

Alpha Wave

  • Regarded as normal wavefront
  • Occur when at rest & eyes closed with active/wandering mind 
  • Associated with decreased level of attention (relaxed/subconscious thinking)
  • Regular Rhythm 
  • Frequency 8-13 Hz ;Amplitude – 50-100 V)
  • Origin – Most evident on parietal & occipital region

Beta Wave 

  • Occurs during Focused attention Irregular rhythm; 
  • At full alert & awake (maximum concentration/conscious thinking)
  • Frequency: 13-30 Hz high frequency & low voltage activity compared to alpha waves.
  • Most evident on parietal & frontal regions.
  • Is recorded from the surface of the scalp during REM sleep. 
  • Barbiturates and benzodiazepines, augment beta waves.

ALPHA BLOCK

  • The replacement of beta rhythm for alpha rhythm is called Arousal / Alerting response / Alpha block
  • Phenomenon occurs during any form of sensory stimulation or mental concentration such as solving arithmetic problems.

Theta Rhythm 

  • Occurs mainly when on slightly more relaxed state
  • Less attentiveness in thinking (Deep subconscious thinking)
  • In Stage 1 of REM.
  • Occur normally in the parietal & temporal regions in children
  • Adults during EMOTIONAL STRESS, particularly during disappointment & frustration 
  • Brain disorders like degenerative brain conditions.
  • Types:
  • Cortical (occurs in humans) 
  • Hippocampal (occurs in mammals other than men, i.e., cat dogs, etc)

Delta Rhythm

  • Collectively referred to as SLOW WAVES
  • In deep sleep (NREM stage 3 & 4) & in state of no thinking
  • Fully relaxed. 
  • Delta waves are abnormal in awake adult.
  • Frequency: 3-5 Hz(lowest); but has largest amplitude & voltage (2 to 4 times > than others).

FARADAY CAGE:

  • EEG cabins completely shielded by a continuous sheet of copper wire mesh to avoid picking up of noise from external electromagnetic disturbances 
  • This shielding is Faraday cage.

Applications of EEG monitoring in Anesthesia

  • Monitoring depth of general anesthesia with 16-lead
  • Assess sedation
  • Awareness & changes in conscious levels
  • Monitor the epileptic activity 
  • Control drug infusions in paralyzed persons 
  • Confirm adequacy of cerebral oxygenation, during cerebrovascular surgery.

Special Pattern Observed in EEG

  • Burst suppression EEG pattern
  • Seen in acute cerebral insults like Hypoxic ischemic encephalopathy/ Anoxic Encephalopathy
  • Phenobarbital administration to lower ICP in traumatic brain injury 
  • Severe hypothermia.
  • Creutzfeldt Jakob disease presents with periodic sharp BIPHASIC wave complexes with frequency about 1/second.
  • Delta waveforms are seen in metabolic encephalopathy.
  • TRIPHASIC slow symmetric and high-voltage wave (2 – 5 /second) pattern is characteristic but non-specific of Hepatic encephalopathy.
  • Absence Seizures shows bursts of bilaterally synchronous & symmetric 3 Hz spike & dome, slow wave activity in EEG.
Exam Question
 

EEG (Berger’s rhythm) 

Types Of Rhythms (Important in sleep-wake cycle) – Bilaterally Symmetrical

  • Alpha
  • Beta
  • Theta
  • Delta

Alpha Wave

  • Occur when at rest & eyes closed with active/wandering mind 
  • Associated with decreased level of attention (relaxed/subconscious thinking)
  • Origin – Most evident on parietal & occipital region
  • Regular Rhythm
  • Frequency 8-13 Hz; Amplitude – 50-100 V)

Beta Wave 

  • Occurs during Focused attention
  • At full alert & awake (maximum concentration/conscious thinking)
  • Irregular rhythm
  • Frequency: 13-30 Hz high frequency & low voltage activity compared to alpha waves.
  • Most evident on parietal & frontal regions.

ALPHA BLOCK

  • Replacement of beta rhythm for alpha rhythm is called Arousal / Alerting response / Alpha block.  
  • Phenomenon occurs during any form of sensory stimulation or mental concentration such as solving arithmetic problems.

Theta Rhythm 

  • Also seen during transition state from wakefulness to sleep. Similar to Stage 1 of REM.
  • Frequency: 4 – 7 Hz
  • Occur normally in parietal & temporal in children, 
  • In adults during EMOTIONAL STRESS, particularly during disappointment & frustration. 
  • Brain disorders like degenerative brain conditions.

Delta Rhythm

  • Collectively referred to as SLOW WAVES
  • In deep sleep (NREM stage 3 & 4) & in state of no thinking
  • Fully relaxed. 
  • Delta waves are abnormal in awake adult.
  • Frequency: 3-5 Hz(lowest); but has largest amplitude and voltage (2 to 4 times > than others).

Farady Cage

  • EEG cabins completely shielded by a continuous sheet of copper wire mesh to avoid picking up of noise from external electromagnetic disturbances 
  • This shielding is Faraday cage.

Special Pattern Observed in EEG

  • Burst suppression EEG pattern
  • Seen in acute cerebral insults like Hypoxic ischemic encephalopathy/ Anoxic Encephalopathy
  • Phenobarbital administration to lower ICP in traumatic brain injury 
  • Severe hypothermia.
  • Creutzfeldt Jakob disease presents with periodic sharp BIPHASIC wave complexes with frequency about 1/second.
  • Delta waveforms are seen in metabolic encephalopathy.
  • TRIPHASIC slow symmetric and high-voltage wave (2 – 5 /second) pattern is characteristic but non-specific of Hepatic encephalopathy.
  • Absence Seizures shows bursts of bilaterally synchronous & symmetric 3 Hz spike & dome, slow wave activity in EEG.
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