EEG and ICP

Question 1

Glasgow Coma Scale values

Answer 1

3: deep unconsciousness
3-9: severe brain injury
9-12: moderate brain injury
13: minor brain injury

Question 2

Normal cerebral physiology (blood flow and O2 requirements)

Answer 2

3-5 mL O2/min/100g tissue (~15-20% of CO)

50 mL blood/min/100g tissue (which delivers ~150 mL O2/min) + ~750 mL blood flow/min to brain

O2 extraction: 35-50% (heart is 60%)

Question 3

Cerebral perfusion pressure equation

Answer 3

CPP = MAP - ICP

Question 4

Range of MAP at which CBF is autoregulated (maintained)

Answer 4

Normally between MAP of 60-160 mm Hg, CBF is maintained.

Post-trauma, this regulation is impaired and lower limit of auto-regulation is moved up.

Question 5

CBF is reduced by..

Answer 5

Head injury
Intracranial hypertension
Hypotension
Hyperventilation 
Vasospasm

Question 6

Monroe-Kellie hypothesis

Answer 6

Skull is a fixed volume of brain (80%), blood (10%), and CSF (10%)

Cerebral Volume = Brain + Blood + CSF

When CV is compressed, CSF decreases first, then venous blood, then arterial blood, then brain (herniation due to non-compliance of brain)

**After venous blood leaves, any further increase in brain volume will result in large ICP changes

Question 7

How does ICP monitoring work at the level of the transducer? (basic)

Answer 7

Note: requires a watertight fluid interface

Deformation of transducer membrane is converted to electrical pulsations, which is amplified and displayed as waveforms

Question 8

Indications for ICP monitoring

Answer 8

-CT indicates hematoma, edema, contusion, or compressed cisterns

• Normal CT with GCS < 8 and 2 of:
  
  • Age > 40
  • Posturing
  • SBP < 90 mm Hg
• Sedation that prevents clinical assessment
• Meningitis and strokes

Question 9

Effect of GA on CBF autoregulation

Answer 9

autoregulation curve of CBF vs MAP becomes more linear

trend: higher BP = higher CBF = higher ICP

Question 10

CBF is increased physiologically by..

Answer 10

dilation of cerebral vasculature due to increase in plasma CO2, which also increases ICP

Question 11

Normal/abnormal ICP ranges

Answer 11

Normal: 7-15 mm Hg

Abnormal: >20 mm Hg

Requires aggressive management: >25 mm Hg

Question 12

Intraventricular drain and transducer

Answer 12

ICP control by CSF drainage

Currently the most accurate transducer we have

External zeroing every time its hooked up to the monitor

Placement needs to be in the superior lateral ventricles 1 and 2 (not the more central ventricles)

Question 13

Intraventricular drain/transducer risks

Answer 13

Bleeding
Blockage
Infection risk
Insertion difficulties

Question 14

Intraparenchymal pressure monitor

Answer 14

• sits right in the brain (parenchyma = actual brain tissue/neurons+glia)
• lower infection risk and hemorrhage risk
• less “drifting” although this still occurs after several days
• less accurate (tends to underestimate ICP)

Question 15

Contraindications of intraparenchymal pressure monitor

Answer 15

Intracranial infection

Coagulopathies

Severe skull fractures

Conditions where CSF drainage is necessary

Question 16

Difference between compliant and noncompliant brain (herniation) in ICP vs Time wave

Answer 16

Noncompliant wave has high peak P2 rebound wave

see slide 23

Question 17

Ways to manage high ICP by decreasing brain water

Answer 17

• Mannitol – filtered but not reabsorbed sugar (gets peed out by kidney); sucks fluid out of brain but only works with intact BBB [.25-1 g/kg]
  - Worry about hypotension with fast mannitol admin
• Lasix = loop diuretics (decreases overall body fluid)
• Corticosteroids

Question 18

Ways to manage high ICP by decreasing CSF volume

Answer 18

CSF drainage (ventricular, lumbar subarachnoid)

Head elevation

Question 19

Ways to manage high ICP by increasing cranial space

Answer 19

Cranionectomy

Question 20

Autoregulation of CBF is impaired by these types of drugs that we use ..

Answer 20

Inhalational anesthetics

Direct acting vasodilators (Ca++ channel blockers, NTG, nitroprusside, adenosine, prostacyclin)

Question 21

Continuous electroencephalogram monitoring

Answer 21

• Monitors superficial pyramidal cells of the cerebral cx ; represents dendritic potentials
• Reflects metabolic activity of the brain
• Very position dependent

Question 22

Indications for EEG

Answer 22

• Craniotomy
• Carotid endarterectomy : one side (Carotid artery) is clamped down, EEG on either side used to figure out whether there is less CBF on clamped side
• Cardiopulmonary bypass
• Depression of brain for cerebral protection
• Extra cranial/intracranial bypass procedures

(generally any procedures in which blood flow to the brain may be significantly affected)

Question 23

Disadvantages of EEG

Answer 23

• Rarely useful for figuring out why Cx dysfunction exists
• Low sensitivity and specificity
• Susceptible to electrical and physio artifacts (including drugs, state of alertness, eye movements, EKG, body movement etc..)
• Small or deep lesions may go undetected

Question 24

EEG: signs of activation vs depression

Answer 24

Activation (light anesthesia, surgical stimulation): high frequency, low voltage

Depression (deep anesthesia, cerebral compromise): low frequency, high voltage

Question 25

EEG: hypnotic states VS waves

Answer 25

Awake: beta waves dominant

Relaxation with eyes closed: alpha wave prominence

Light anesthesia: increased beta waves, decreased alpha waves (transition into Stage II)?

Deepening of anesthesia: increase in slow wave activity (delta and theta waves), decrease in alpha and beta waves

Cortical silence : burst suppression

Question 26

EEG: agents and factors that activate

Answer 26

Low MAC volatiles

Low dose barbs and benzos

Low dose etomidate

N2O

Ketamine

Mild hypercapnia

Surgical stimulation

Early hypoxia

Question 27

EEG: agents and factors that depress

Answer 27

1-2 MAC volatiles

Medium to high dose barbs, propofol, etomidate

Narcotics (dose dependent)

Hypocapnia

Hypothermia

Late hypoxia