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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