Monitoring EEG Flashcards
What was the name of the brain that Igor picked up?
Abby Normal
Why do we monitor the brain? (4)
- Without a functional brain, we cease to exist.
- The brain is the organ least able to withstand hypoxia.
- There is no sustitute.
- Planned therapeutic intervention (coma, burst suppress.)
What operations can result in a stroke? (7)
Carotid endarterectomy
Cerebral aneurysm
Brain tumor
Thoracic aorta
Cardiac operations
Thracoabdominal aorta
Thoracic endovascular repair
How do we monitor the brain function?
Electrical activity–EEG, Processed EEG (spectral edge, power spectrum)
Cortical motor evoked responses–Electromagnetic cortical stimulation (MEP motor evoked potential)
Sensory evoked responses–Visual evoked potentials, Brainstem auditory evoked potentials, Somatosensory evoked responses
Wake up test
What methods are useful for neurological monitoring of blood flow? (6)
Transcranial doppler ultrasound
Jugular venous oxygen saturation
Cerebral oximetry
Electroencephalogram (indirectly)
Sensory evoked potentials (indirectly)
Motor evoked potentials (indirectly)
What methods are useful for neurological monitoring electrical function? (4)
Electroencephalogram
Sensory evoked potentials
Electromyogram
Motor evoked potentials
What methods are useful for neurological monitoring anesthetic effect? (2)
Electroencephalogram
Sensory evoked potentials
What can electroencephalography (EEG) be used to detect? (4)
Brain ischemia
Seizure activity
Stroke
Assess metabolic activity
What can somatosensory evoked potential (SSEP) be used to detect? (2)
Sensory nerve ischemia and injury
Spinal cord ischemia and injury
What can motor-evoked potential (MEP) be used to detect? (2)
Motor nerve ischemia and injury
Spinal cord ischemia and injury
What can brainstem auditory evoked potential (BAEP) be used to detect? (2)
Injury to auditory pathway
Injury to CN 8 (vestibulocochlear)
What can visual-evoked potential (VEP) be used to detect? (3)
Integrity of visual pathway
Injury to occipital lobes
Injury to optic nerve
What tools can be used to detect peripheral nerve injuries? (3)
Nerve integrity monitor
Electromyelogram
Nerve conduction study
What’s depicted?
Electroencephalogram 10-20 System
What’s depicted?
What does F, T, O, and P represent?
Electrocorticogram (ECoG)
Frontal
Temporal
Occipital
Parietal
What do even #’s on the electrocorticogram represent?
Odd #’s?
Even numbers on right side of head
Odd on left side of head
What type of monitor has electrodes on the brain itself, to detect seizure activity, for example?
Electrocorticogram (ECoG)
What are the name of the electrodes used during EEG monitoring?
Montage
What type of activity does this raw (unprocessed) EEG depict?
“light” sleep
What do each of these sets represent?
They are montages of the electrodes being used.
Note: This image illustrates the heterogenous appearance of EEG recorded simultaneously from many sites.
What state does this indicate?
Awake, low voltage (random, fast)
What state does this indicate?
Drowsiness
What state does this indicate?
What is encircled?
Stage 2
sleep spindle
What state does this indicate?
REM sleep
Note the sawtooth waves.
EEG pattern from wakefulness is characterized by ________.
EEG pattern from sleep is characterized by _______.
desynchrony
synchrony
What is encircled?
Classic spindle EEG waves
Where do you see better spindle waves than the book has denoted?
What are the corresponding frequency bands of the EEG for the following frequencies?
< 4Hz
4 to 7
8 to12
> 12
Delta
Theta
Alpha
Beta
Note: You can see EEG is interfered by heart and muscle activity.
EEG is prone to artifact because it is a very sensitive amplifier. True or false?
True.
What do the presence of delta waves indicate?
Deep anesthesia
What do the presence of theta waves indicate?
Light sleep
Light anesthesia
What do the presence of beta waves indicate?
Sedation
Light anesthesia
As sleep is induced, what is the order of frequency bands encountered?
Alpha → Beta →Theta → Delta
Note: Delta look like an ischemic brain, making diagnosis difficult.
Label:
Complex phase = spindle activity
Note: It is difficult to distinguish spindle activity from burst suppression, but spindle activity has more high frequency components within it whereas burst suppression has low frequency comp.
What is normal cerebral blood flow?
50ml / (100g*min)
EEG becomes abnormal when cerebral blood flow decreases to what?
20 - 25 ml / (100g*min)
Cellular survival threatened when CBF decreases below what?
12 mL / (100g*min)
Deep anesthesia and ischemia produce the same EEG patterns. True or false?
True.
________ of the EEG is used during aneurysm clipping.
Burst suppression
Approximately half of the total energy consumed in the brain is used by neurons during depolarization and repolarization. True or false?
True.
Of total cerebral O2 metabolism (3.5ml/100g*min), how much is dedicated to:
electrophysiologic activity
maintenance of cellular integrity
both are 50%
What drugs and physiology will result in increased frequency on the EEG? (5)
Hyperoxia
Hypoxia: initial
Barbiturates: small dose
N2O: 30 - 70%
Inhalation agents < 1 MAC
What drugs and physiology will result in decreased frequency, increased amplitude on the EEG? (2)
Hypoxia, mild
Inhalation agents > 1 MAC
What is the order of EEG changes with increasing hypoxia? (4)
Increased frequency (initial)
Decreased frequency, increased amplitude (mild)
Decreased frequency, decreased amplitude (marked)
Electrical silence (severe)
Label
Normal
Mild ischemia
Severe ischemia
Deep anesthesia and ischemia produce the same EEG. True or false?
True.
If you want to place pt in burst suppression, what MAC is needed?
>1.5 MAC
What happens to spectral edge frequency as MAC levels increase?
Decreases.
Burst suppression ratio is an EEG derived variable defined as the percentage of time in an EEG sample that the waveform is isoelectric. True or false?
True.
As you increase by 0.5 MAC increments, what do you notice occurring to the waveform?
High frequency, low amplitude
Decreased frequency, increased amplitude, and so on.
What does it mean when the spectral edge frequency is 10?
The spectral edge is at or below 10 Hz, which is fairly low and close to burst suppression.
What anesthetic agents cause burst suppression at > 1.5 MAC? (3)
Isoflurane
Desflurane
Sevoflurane
(Also, Enflurane)
What anesthetic drugs will NOT cause burst suppression? (5)
N2O (alone)
Ketamine
Benzos
Opiates
Dexmedetomidine
What anesthetic drugs will cause burst suppression at high doses? (3)
Barbiturates
Etomidate
Propofol
What occurs to the EEG with hypothermia?
Decreased frequency and amplitude because the brain will shut down.
What will occur to the EEG with pt on CPB with volatile agent?
EEG will be nearly isoelectric.
Note the lower graph depicted at temp ~18*C.
In a processed EEG, a raw wave is digitized using a FFT (fast fourier transformation) to display a power spectrum. True or false?
True.
The 3 variables that have been used to describe EEG changes during anesthesia are what?
Mean, median, and spectral edge frequencies
What is spectral edge frequency?
95%
What is depicted?
Compressed spectral array
Interpret:
What happens to MAP?
Top: Awake
Middle: Asleep, see MAP fall here
Bottom: Waking up
Label the arrays:
Correlate the 2 arrays:
What array is displayed?
What is the spectral edge frequency?
Density spectral array
17.2
In conclusion, as you get sleepier, the frequencies get _____ and the amplitudes get ______.
lower
higher
At the initiation of anesthesia, or hypoxia, the frequencies get ______ and the amplitude _____.
higher
lower
(As if in excitatory phase)
With increased anesthesia, or as hypoxia worsens, the frequencies ____ and the amplitudes _______
decrease
increase
