EEG and ICP Flashcards by Helen Wang

What is normal cerebral blood flow? How much O2 does this deliver?

50 ml/min/100g tissue

Delivers 150 ml O2/min

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What is the energy requirement of the brain?

3-5 ml O2/min/100g tissue

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How much O2 does the brain extract?

35-50%

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What is the equation of cerebral perfusion pressure?

CPP = MAP - ICP

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Cerebral blood flow is impaired

Post trauma

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Auto regulation of cerebral blood flow

Increases at the lower limit

Graph - as MAP increases, so does CBF… But plateaus in the middle…?

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CBF is reduced by

Head injury
Intracranial hypertension
Hypotension
Vasospasm
Hyperventilation

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Intracranial pressure can be directly monitored by

Subdural/subarachnoid bolts
Epidural transducers
Intraparenchymal fiber optic devices
Ventricular catheters

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What is the Monroe-Kellie hypothesis?

The skull is a fixed volume and changes in one unit is balanced by the others.

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What are the three components of the Monroe-Kellie hypothesis?

Blood, brain, cerebral spinal fluid

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What are the percentages of the units that make up ICP?

Brain mass - 80%
Blood flow - 10%
CSF - 10%

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T or F. ICP monitoring does not require a watertight fluid interface?

False

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How is brain activity converted to a waveform?

Deformation of transducer membrane
Converted to electrical pulsations
Amplified
Displayed as a waveform

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T or F. Catheter tip transducers need to be zeroed prior to insertion.

True

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External transducers are zeroed

Anytime

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Monitoring ICP is important in

Head injury
Poor grade subarachnoid hemorrhage
Intracerebral hematoma
Meningitis
Stroke

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What are normal ICP values? Abnormal?

Normal: 7-15 mmHg
Abnormal: >20 mmHg

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Aggressive management of ICP is indicated at what value?

> 25 mmHg

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Elevated ICP causes

Herniation of internal and external brain
Distortion of cranial nerves and vital neurological centers
Impeded cerebral perfusion
Loss of CSF
Reduced venous blood flow

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What are the pros of intraventricular drain and transducer?

Gold standard
ICP control by CSF draining
External zeroing

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What are the cons of intraventricular drain and transducer?

Bleeding
Blockage
Infection

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What is the correct placement of intraventricular catheters?

Lateral ventricle (frontal horn)

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What is the position of the transducer?

Level with the meatus of the ear

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What are the pros of the intraparenchymal pressure monitor?

Less infection risk
Less risk of hemorrhage
Excellent metro logical properties (less drift)

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What are the cons of the intraparenchymal pressure monitor?

Underestimates very high ICP | Drift becomes a problem after several days

What are contraindications for using intraparenchymal pressure monitoring?

Intracranial infections Coagulopathies Severe skull fracture CSF drainage necessary

What are the three phases of ICP waveforms?

P1: percussion wave (arterial pulsations) P2: rebound wave (intracranial compliance) P3: dichrotic wave (venous pulsations)

How is ICP managed?

Decrease brain water | Reduce CSF volume

What are ways to decrease brain water?

Hyperosmolar diuretics: mannitol w/ intact BBB Loop diuretics: Lasix Corticosteroids

What is the dosage of mannitol?

.25-1g per kg

CSF can be reduced from drainage by

Ventricular Lumbar subarachnoid Head elevation

Auto regulation is impaired by

Inhaled anesthetics | Direct acting vasodilators

What are examples of direct acting vasodilators?

``` Adenosine Prostacyclin Calcium channel blockers Nitroglycerin Nitroprusside ```

Transcranial Doppler Ultrasonography

Continuous or intermittent monitoring of CBF velocity

What is Transcranial Doppler Ultrasonography most useful for?

Vasospasm post subarachnoid hemorrhage

Does vasospasm cause increased or decreased CBF velocity?

Increased (due to Posseiulle's Law)

For TCD, what allows for monitoring independent of rising ICP?

ICA:MCA flow Ratio of internal carotid artery to middle cerebral artery flow

What is electroencephalogram monitoring?

Summation and recording of postsynaptic potentials from the pyramidal cells of the cerebral cortex Reflects the metabolic activity of the brain

EEG was first used by

Hans Berger in 1924

A tracing of voltage fluctuations versus time recorded from electrodes placed over scalp in a specific array

EEG

Represents fluctuating dendritic potentials from superficial cortical layers Required amplification

Part of the brain not sampled well by EEG

Deep parts of the brain

International 10-20 system of electrode placement

Electrodes spaces at ten or twenty percent of distances between specified anatomical landmarks

More than 21 electrodes can be added on an EEG to

Increase spatial resolution Record from specific areas Monitor electrical activity

Odd electrodes are placed Even electrodes are placed

On the left On the right hemisphere

Disadvantages of EEG

Detects cortical dysfunction, but not etiology Low sensitivity and low specificity Subject to electrical and physiologic artifacts Influenced by alertness, hypoglycemia, and drugs Small or deep lesions might not produce EEG abnormality Limited time sampling and spatial sampling

Indications for EEG

Craniotomy for cerebral aneurysm clipping when a temporary clip is used Carotid endarterectomy under GA Cardiopulmonary bypass Extra cranial intracranial bypass Pharmacological depression of brain for "cerebral protection"

Beta waves

13-30 Hz Awake and alert

Alpha waves

8-13 Hz Closed eyes, relaxed

Theta waves

4-7 Hz Young children Drowsiness in older children or adults

Delta waves

0-4 Hz Deep sleep, deep sedation

Suppression event

Very deep sedation, hypothermia, and ischemia

EEG artifact

``` Eye induced - blinks, movement, extra ocular muscle activity Gloss kinetic artifacts Poor grounding IV drips Body movement EKG artifact ```

Relaxation with eyes closed

Alpha waves predominance

Light anesthesia

Increase in beta | Decrease in alpha

Deepening of anesthesia

Increase in slow wave activity, delta 5 and theta 8

Cortical silence

Burst suppression

EEG is not

An output of the spinal cord or predictor of movement

Activation

High frequency Low voltage Light anesthesia Surgical stimulation

Depression

Low frequency High voltage Deep anesthesia Cerebral compromise

Most anesthetics produce

A biphasic pattern... Initial activation... Followed by dose dependent depression

Agents that activate EEG

``` Sub anesthetic inhalationals Low dose barbs and benzos Small doses of etomidate N2O Ketamine ```

Agents that depress EEG

1-2 MAC gases Barbs/propofol/etomidate Narcotics - dose dependent

Other things that influence - activate

Mild hypercapnia Surgical stimulation Early hypoxia

Other things that depress

Hypocapnia Hypothermia Late hypoxia