EEG and ICP Flashcards Preview

I & M 441 > EEG and ICP > Flashcards

Flashcards in EEG and ICP Deck (27)
Loading flashcards...
1

Glasgow Coma Scale values

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

2

Normal cerebral physiology (blood flow and O2 requirements)

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%)

3

Cerebral perfusion pressure equation

CPP = MAP - ICP

4

Range of MAP at which CBF is autoregulated (maintained)

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.

5

CBF is reduced by..

Head injury
Intracranial hypertension
Hypotension
Hyperventilation
Vasospasm

6

Monroe-Kellie hypothesis

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

7

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

Note: requires a watertight fluid interface

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

8

Indications for ICP monitoring

-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

9

Effect of GA on CBF autoregulation

autoregulation curve of CBF vs MAP becomes more linear

trend: higher BP = higher CBF = higher ICP

10

CBF is increased physiologically by..

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

11

Normal/abnormal ICP ranges

Normal: 7-15 mm Hg

Abnormal: >20 mm Hg

Requires aggressive management: >25 mm Hg

12

Intraventricular drain and transducer

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)

13

Intraventricular drain/transducer risks

Bleeding
Blockage
Infection risk
Insertion difficulties

14

Intraparenchymal pressure monitor

-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)

15

Contraindications of intraparenchymal pressure monitor

Intracranial infection

Coagulopathies

Severe skull fractures

Conditions where CSF drainage is necessary

16

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

Noncompliant wave has high peak P2 rebound wave
(see slide 23)

17

Ways to manage high ICP by decreasing brain water

-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

18

Ways to manage high ICP by decreasing CSF volume

CSF drainage (ventricular, lumbar subarachnoid)

Head elevation

19

Ways to manage high ICP by increasing cranial space

Cranionectomy

20

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

Inhalational anesthetics

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

21

Continuous electroencephalogram monitoring

-Monitors superficial pyramidal cells of the cerebral cx ; represents dendritic potentials

-Reflects metabolic activity of the brain

-Very position dependent

22

Indications for EEG

-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)

23

Disadvantages of EEG

-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

24

EEG: signs of activation vs depression

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

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

25

EEG: hypnotic states VS waves

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

26

EEG: agents and factors that activate

Low MAC volatiles

Low dose barbs and benzos

Low dose etomidate

N2O

Ketamine

Mild hypercapnia

Surgical stimulation

Early hypoxia

27

EEG: agents and factors that depress

1-2 MAC volatiles

Medium to high dose barbs, propofol, etomidate

Narcotics (dose dependent)

Hypocapnia

Hypothermia

Late hypoxia