EEG And ICP Monitoring

Question 1

How much energy does the cerebrum require?

Answer 1

3-5 ml O2/min/100g tissue

Question 2

Normal Cerebral Blood Flow is ___.

Answer 2

50 ml/min/100 g tissue 750 ml/min for brain Delivers 150 ml O2/min

Question 3

O2 extraction from cerebral blood flow is:

Answer 3

35-50%

Question 4

What is the equation for Cerebral Perfusion Pressure (CPP)?

Answer 4

CPP = MAP - ICP

Question 5

Cerebral blood flow is:

Answer 5

• Tightly regulated except post-trauma

Question 6

Cerebral blood flow stays around ____, as long as MAP is between _____ mm Hg.

Answer 6

50 ml/100g/min , 50-100

Question 7

CBF is reduced by

Answer 7

1. Head injury 2. Intracranial hypertension 3. Hypotension 4. Hyperventilation 5. Vasospasm

Question 8

Ways of directly monitoring ICP:

Answer 8

1. Ventricular catheters 2. Subdural/subarachnoid bolts 3. Epidural transducers 4. Intraparenchymal fiber optic devices

Question 9

What is the Monroe-Kellie hypothesis:

Answer 9

The skull is a fixed volume. If one or more of these components increases, ICP rises: - Blood - CSF - Brain

Question 10

ICP determined by:

Answer 10

• Brain mass (80%) - Blood flow (10%) - CSF volume (10%)

Question 11

ICP monitoring physical set up

Answer 11

1. Connection of device to transducer 2. Watertight fluid interface 3. Deformation of transducer membrane converted to electrical pulsations and amplified and displayed as a waverform

Question 12

Zeroing of ICP Monitors requires:

Answer 12

• Zeroing to room air - Catheter tip transducers only zeroed prior to insertion - External transducers can be zeroed anytime

Question 13

Indication for ICP monitoring:

Answer 13

-GCS < 8 (or higher if CT of concern {Hematoma, Edema, Contussion, etc}) -Normal CT with GCS 40 2. Posturing 3. SBP < 90 mm Hg -Sedation precluding clinical assessment

Question 14

ICP monitoring is useful in:

Answer 14

1. Head injury 2. Poor grade SAH 3. Intracerebral hematoma 4. Meningitis 5. Stroke 6. Allows calculation of CPP 7. Info on intracerebral compliance

Question 15

ICP Values:

Answer 15

Normal: 7-15 mm Hg Abnormal: > 20 mm Hg If > 25 mm Hg, aggressive management indicated

Question 16

High ICP:

Answer 16

will cause internal or external herniation of the brain, distortion and pressure on cranial nerves and vital neurological centers

Question 17

When ICP is elevated cerebral perfusion will be:

Answer 17

Impeded and operating conditions difficult or impossible

Question 18

When brain volume increases

Answer 18

loss of CSF and reduction of venous blood volume act to compensate

Question 19

Subdural hematoma can lead to:

Answer 19

Tentorial herniation

Question 20

Hemorrhage can lead to:

Answer 20

Subfalcine herniation

Question 21

Devices to measure ICP:

Answer 21

Question 22

What is the Gold Standard of ICP measuring?

Answer 22

Intraventricular drain and transducer b/c you can control ICP by CSF drainage and zero externally

Question 23

What are the contraindications of intraventricular drain and transducer?

Answer 23

• Bleeding
• Blockage
• Infection risk
• Insertion difficulties

Question 24

Which ventricle is the intraventricular catheter placed?

Answer 24

Lateral ventricle (frontal horn)

Question 25

What are the positive points of the intraparenchymal pressure monitor?

Answer 25

• Lower infection risk
• Less risk of hermorrage
• Excellent metrological properties (less drift)

Question 26

What are the negatives to a intraparenchymal pressure monitor?

Answer 26

• Underestimate very high ICP
• Drift a problem after several days

Question 27

What are the contraindications of intraparenchymal pressure monitors?

Answer 27

• Intracranial infection
• Coagulopathies
• Severe skull fractures
• Conditions where CFS drainage is necessary

Question 28

Phase 1 of the ICP Waveform:

Answer 28

P1: Percussion wave (arterial pulsation)

Question 29

Phase 2 of ICP waveform:

Answer 29

P2: Rebound wave (Intracranial compliance)

Question 30

Phase 3 of ICP waveform:

Answer 30

P3: Dichrotic wave (venous pulsations)

Question 31

ICP Management: Decrease brain water w/

Answer 31

• hyperosmolar diuretics (Mannitol w/ intact BBB 0.25 - 1 g/kg)
• Loop diuretics (Lasix)
• Corticosteroids

Question 32

ICP Management: Reduce CSF Volume by:

Answer 32

• Drainage (Ventricular, lumbar subarachnoid, head elevation)

Question 33

Auto regulation is impaired by:

Answer 33

• Inhalational anesthetics
• Direct acting vasodilators (Adenosine, Prostacyclin, Ca++ Channel blockers, NTG, Nitroprusside)

Question 34

Transcranial Doppler (TCD) Ultrasonography:

Answer 34

• Allows CBF velocity measurement (continuous or intermittent)
• Most usefule for vasospasm post subarachnoid hemorrhage
  
  • Vasospasm: increased flow velocity
  • Ratio of ICA:MCA flow allows monitoring independent of rising ICP

Question 35

Continuous Electroencephalogram (EEG) Monitoring:

Answer 35

The summation and recording of postsynaptic potentials from the pyramidal cells of the cerebral cortex; reflects metabolic activity of the brain

Question 36

EEG is a tracing:

Answer 36

Of voltage fluctuations versus time recorded from electrodes placed over scalp in specific array; represent fluctuating dendritic potentials from superficial cortical layers;

Question 37

Disadvantages of EEG:

Answer 37

• Required Amplification
• Deep parts of the brain are not well sampled
• Detects cortical dysfunction but rarely discloses its etiology
• Relatively low sensitivty and specificty
• Subject to electrical and physiological artifacts
• Influenced by state of alertness, hypoglycemia, drugs
• Small or deep lesions might not produce an EEG abnormality
• Limited time sampling and spatial sampling

Question 38

Placement of EEG Electrodes:

Answer 38

• Usually 21 or more
• Spaced at 10 or 20% of distances btwn specified anatomic landmarks
• Odd # of electrodes over left, even over right

Question 39

Indication for EEG:

Answer 39

• Craniotomy for cerebral aneurysm clipping when a temporary clip is used
• Carotid Endarterectomy (under GA)
• Cardiopulmonary bypass
• Extra cranial-intracranial bypass procedures
• Pharmacologic depression of brain for “cerebral protection”

Question 40

EEG Waveforms: Beta

Answer 40

13 - 30 Hz; Awake and alert (short and frequent)

Question 41

EEG Waveforms: Alpha

Answer 41

8-13 Hz; closed eyes, relaxed (Tall and frequent)

Question 42

EEG Waveforms: Theta

Answer 42

4-7 Hz Tall and infrequent (GA)

Question 43

EEG Waveforms: Delta

Answer 43

0-4 Hz, Deep sleep, deep sedation (Very tall and very infrequent)

Question 44

EEG Artifacts

Answer 44

• Eye-induced artifacts (includes eye blinks and eye mvmt)
• Gloss kinetic artifacts
• Poor grounding
• IV drips
• Body mvmt
• EKG artifact

Question 45

EEG Monitors: Continuous Electroencephalography

Answer 45

• BIS algorithm
• Snap
• State entropy/Respone entropy (Datex-Ohmeda algorithm)
• SEDLine monitor (Patient state analyzer)
• A-Line AEP Monitor/2 (EEG plus AEP) and Cerebral State Monitor (EEG Only)
  
  • EEG and Auditory Evoked Potentials
• Narcotrend (EEG Monitor)

Question 46

The EEG is NOT

Answer 46

A predictor of mvmt under GA

Question 47

EEG Monitoring: Activation

Answer 47

High frequency, Low voltage; Light Anesthesia, Surgical stimulation

Question 48

EEG Monitoring: Depression

Answer 48

Low frequency, high voltage; Deep anesthesia, cerebral compromise

Question 49

Agents That Activate

Answer 49

• Subanesthetic inhalationals
• Low dose barbiturates/benzodiazepines
• Small doses of etomidate
• N2O
• Ketamine
• Mild hypercapnia
• Stimulation (surgical)
• Early hypoxia

Question 50

Agents That Depress

Answer 50

• 1-2 MAC gases
• Barbiturates/propofol/etomidate
• Narcotics- dose dependent
• Hypocapnia
• Hypothermia
• Late hypoxia