Neuro Monitoring Flashcards Preview

I&M for Anesthesia - Fall 2013 > Neuro Monitoring > Flashcards

Flashcards in Neuro Monitoring Deck (48):
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Motor Evoked Potentials (MEP) - Pathway

True MEP are stimulated on the cortical motor strip and recorded by sensors on peripheral muscle
Transcranial MEP (TceMEP) are stimulations by scalp electrodes placed over motor strip
Direct spinal cord MEP stimulation via epidural electrodes

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MEP - Appropriate Measurement

Motor strip surgeries
Spine surgery

2

MEP - Limitations of Measurement

Interference of anesthetics
Difficulty in establishing baseline due to electrocautery, NMB, and positioning
Does pt have diagnosed disease such as multiple sclerosis

3

MEP - Compatibility/Interference

Volatile/N2O - increase latency, decrease amplitude
Propofol/benzos/dexmetetomidine - increase latency, decrease amplitude
Etomidate - decreases latency, increases amplitude
Ketamine - no effect latency, increase amplitude
Opiates - no effect
NMB - eliminates

4

MEP vs EMG

EMG is a measurement, MEP is a measured response

5

MEP - Best Method

Protect ETT from biting
Avoid additional MR after intubation
Steady infusions, avoid boluses
TIVA
Realize the pt will move

6

EMG - Appropriate Measurement

Pedical screw placement or other hardware placement

Works by stimulating the hardware, if EMG is detected, then hardware is through the nerve

7

Electromyographic (EMG) - Pathway

Is a local measurement of muscle activity

No pathway exists

8

EMG - Compatibility/Interference

Volatile - no effect at 1 MAC
NMB - eliminates response
Other - no effect

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EMG - Limitations of Measurement

Intrinsic muscle disease or NMJ disease such as myasthenia gravis or polio

10

EMG - Best Method

Protect ETT from biting
Be cautious of needles
No NMB after intubating dose

11

NIM EMG - Pathway

Trigeminal... Glossopharyngeal... Internal branch superior laryngeal... Recurrent laryngeal

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NIM EMG - Appropriate Measurement

Neck Dissection
Thyroidectomy
Parathyroidectomy
Brainstem surgery
Carotid surgery

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NIM EMG - Limitations of Measurement

Avoidance of paralytics may result in requiring an increase in anesthetic doses which may result in suppression of EMG signal
Only tests nerve tract patency, airway compromise may occur with hypocalcemia following parathyroidectomy
Not for long term intubation
Decreased signal can indicate nerve stretching, not true damage
Expense
No pediatric sizes

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NIM EMG - Compatibility/Interference

NMB - eliminates
Local/topical - decreases

Other - no effect

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NIM EMG - Best Placement

Avoid paralytic agents
Do not se gel or lubricant on tube
No topical anesthetic
Visualize placement
Not exact relation to incisors/gum
Note orientation of anterior marking
Save all included wires and connectors
Anticipate 0.5-1 larger tube than expected
Dispose in sharps container
Do not leave in place for long term intubation

16

Brainstem Auditory Evoked Potentials (BAEP) - Pathway

Assesses CN VIII (vestibulocochlear aka acoustic nerve through its tract to the pons)

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BAEP - Tract Anatomy

Ear stuff

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BAEP - Appropriate Measurement

Vestibular nerve
Acoustic neurons
Facial nerve
Cochlear nerve

Acoustic neuroma on vestibulocochlear nerve puts pressure on facial nerve

19

BAEP - Limitations of Measurement

Difficult to assess permanent injury vs stretch

Often used in surgery with no other alternative (leave a bit of tumor vs hearing loss)

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BAEP - Compatibility/Interference

No effect

21

BAEP - Best Method

Plain ol anesthesia

Decrease of BAEP is fairly reliable indicator of Stage 4

22

Visual Evoked Potentials - Pathway

Retina to occipital cortex

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Visual Evoked Potentials - Tract Anatomy

Visual cortices
Optic chiasm
Optic nerve

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Visual Evoked Potentials - Appropriate Measurement

Craniopharyngiomas

Suprasellar masses

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Visual Evoked Potentials - Limitations of Measurement

Very sensitive to any anesthetic technique

Not considered reliable intraoperatively due to high incidence of false positives

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Visual Evoked Potentials - Compatibility/Interference

Volatile/benzo/opiates - increase latency, decrease amplitude
N2O - no effect latency, decrease amplitude
Propofol/dexmedetomidine** - decreases
Etomidate - increases
Ketamine - no effect latency, increase amplitude
NMB - ???

27

Visual Evoked Potentials - Best Method

No established recommendations
Seldom utilized
Avoid hypotension
Avoid high conc of single agent

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Facial Nerve Monitoring - Pathway

Facial nerve...

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Facial Nerve Monitoring - Tract Anatomy

7th cranial nerve

Brainstem

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Facial Nerve Monitoring - Appropriate Measurement

Wide local exclusions of face and ear
Parotid surgery
Maxillary surgery
Mastoid-translabrynthine surgery
Excision of acoustic neuromas
Brainstem surgery (pontine and medullary)

31

Facial Nerve Monitoring - Limitations

Exacting needle placement

Can get response from V2 and V3 nerve

32

Facial Nerve Monitoring - Compatibility/Interference

NMB - eliminates
Dexmedetomidine - none?
Others - none

33

Facial Nerve Monitoring - Best Method

Protect ETT from biting
No scalp block
Watch for needle displacement

34

Cortical Mapping - Tract Anatomy

Precentral - Motor cortex "positivity"

Postcentral - Somatosensory cortex "negativity"

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Cortical Mapping - Appropriate Measurement

Exact mapping of sensory and motor areas of cerebral cortex

Measures plasticity

36

Cortical Mapping - Limitations

Placement of electrodes can be difficult

Placement can be impossible of craniotomy window is not aligned with frontal cortex strips

37

Cortical Mapping - Compatibility/Interference

Volatile/propofol/opiate/NMB - no effect
Nitrous - interferes
Etomidate/ketamine - enhances
Benzos - decreases
Dexmedetomidine - unknown

38

Cortical Mapping - Best Method

Optimize cerebral perfusion

Limit cerebral edema

39

Somatosensory Evoked Potentials (SSEP) - Pathway

Stimulus... Peripheral nerve...
Dorsal root ganglion...
1st order fibers ipsilateral posterior columns...
2nd order fibers crossing to opposite side...
Medial lemniscus to thalamus...
3rd order fibers to frontal parietal cortex

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SSEP - Tract Anatomy

Gray matter... White matter...

41

SSEP - Appropriate Measurement

Spinal surgery with instrumentation where manipulation can result in disruption of blood supply to anterior spinal cord
Brachial plexus surgery
Surgery involving sensory cortex
Thalamic surgery
Thoroco-abdominal aneurysm repair
Repair of aortic coarctation
Carotid surgery to assess cortex integrity
Aneurysm - especially after anterior cerebral

42

SSEP - Limitations

False negatives - 1% for neuro cases, higher for aortic
False positives
Not a true measure of motor tract integrity
Greater loss of CBF needed for SSEP change vs EEG
Electrode placement may not be feasible in aneurysm surgery due to location of surgical field

43

SSEP - Compatibility/Interference

Volatile/benzos/opiates - increases latency, decreases amplitude
Nitrous - no effect latency, decreases amp
Propofol/dexmedetomidine**- decreases latency and amp
Etomidate - increases latency and amp
Ketamine - no effect latency, increases amp
NMB - increases signal

44

SSEP - Best Method

Anesthesia - TIVA propofol ketamine infusion
Analgesia - opioid or ketamine infusion
Paralysis - any
Infuse agents or pressors instead of administering as a bolus
Inform monitoring staff of changes in anesthetic agents
1/2 MAC is OK for board exams
Normotensive and normothermic patients

45

Change in signal

Alert surgeons
Review recent changes
Assess perfusion
Normalize ABG
Normalize BP
Consider change to technique to enhance

46

Functional Magnetic Resonance Imaging (fMRI) - Advantages

Differentiates left brain for right brain function

Capacity to show exact location responsible for certain tasks such as eloquent speech and motor areas

47

fMRI - Disadvantages

Neural conduction time is much more rapid than MRI pulse sequence
Cost
Time and training of personnel
Multiple foci may show up
Difficult to approximate in relation to surgical site
Does not show tracts, only shows cortical grey matter
Pt has to be awake during scan and be cooperative