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Flashcards in Neuro Monitoring Deck (24)
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1

Over-riding principles for neurophysiologic monitoring

-Pathway monitored must be at risk and an option for intervention must be available if changes occur

-Baseline testing required prior to any intervention

-10/50 rule: 10% increase in latency or 50% decrease in amplitude = cause for concern!

2

MEP description

Motor evoked potentials are stimulated on Cx motor strip and recorded by sensors in corresponding peripheral muscle

Most appropriate for motor strip surgeries or spine surgery

3

MEP limitations

Anesthetic interference

Difficulty in baseline establishment due to NMB, positioning, electrocautery

Pathologies such as MS can interfere

4

MEP interference from anesthetics (limitations)

slide 12

5

MEP considerations

-Protect ETT from biting

-Avoid additional muscle relaxant after intubation

-Avoid boluses (opt with steady infusions)

-Consider TIVA w propofol and ketamine

-Realize pt will move

6

EMG (electromyographic)

EMG: needle in muscle measures muscle's flexion; a local measurement of muscle activity

Can be used to confirm integrity of hardware placement,

7

Differences between EMG an MEP:

EMG is a measurement, MEP is a measured response

MEP source is localized to a region on the motor strip; EMG has no specific source that's being monitored/evoked

8

EMG limitations

Intrinsic muscle diseases (myesthenia gravis, polio, etc..) and NMB

9

NIM-EMG method

-looking at recurrent laryngeal nerve

-"twitch" provocation and signal monitoring

-when NIM ETT tube is placed, the contact surface (blue strip) must go between the vocal cords

10

NIM indications

Neck Dissection
Thyroidectomy
Parathyroidectomy
Brainstem Surgery
Carotid Surgery

11

NIM limitations

Avoidance of paralytics may require increase in anesthetic doses which may result EMG suppression

Only tests nerve tract patency

Not for long term intubation
-High pressure, low volume cuff = cannot use for long cases, can cause tracheal necrosis

Decreased signal may indicate nerve stretching, not true damage

Expense ($300 tube)

No pediatric sizes (only 6.0, 7.0, 8.0)

12

NIM-EMG considerations

Avoid paralytics

Do not use lubricant or gel; not topical anesthetics either

Anticipate 0.5-1 size larger tube than you might think

Dispose in sharps container

Do not leave in place for long term intubation

13

BAEP (brainstem auditory evoked potentials) assesses..

CN VIII (vestibulocochlear nerve) through its tract to the Pons

14

Limitations to BAEP

difficult to assess permanent injury vs stretch

other then that, no other real limitations (can be used with GA); specific in the nerve it tracks though

15

BAEP uses

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

decrease in BAEP is a fairly reliable indicator of stage 4 anesthesia (overdose)

16

Visual Evoked Potentials

-Rarely done

-Used to assess the optic nerve

-Almost everything interferes with it (slide 39)

17

Facial nerve monitoring - what does it monitor?

Monitors the various endpoints of CN VII (facial nerve)

18

When should facial nerve monitoring be used?

Wide excisions around face and ear

Parotid surgery (facial nerve goes through the parotid gland, the major bilateral salivary gland)

Surgeries around the maxillary or mastoid

Excision of acoustic neuromas

Brainstem surgery (due to CN VII's proximity to it)

19

Limitations of facial nerve monitoring

Needle placement needs to be exact

Tongue and ETT really needs to be protected in this situation

20

Cortical mapping limitations

N2O, Versed (benzos)

Craniotomy window needs to be aligned with frontal cortex strips

21

SSEP (somatosensory evoked potentials) pathway

Stimulus --> Peripheral Nerve --> DRG --> Ipislateral posterior columns (1 order fibers) --> contralateral columns (2 order fibers) --> medial lemniscus --> thalamus --> 3rd order fibers to frontal parietal Cx --> Measurement electrodes

22

SSEP indications

Spinal surgeries where blood supply to anterior spinal cord needs to be watched

Brachial plexus surgery

Sensory Cx surgeries

Thalamic surgery

Carotid surgery

Aneurysm surgeries

Aortic coarctation repairs

23

SSEP limitations

SSEP's are not 100% predictors of whether or not patient's muscular/nerve integrity is compromised

Greater loss of CBF needed for SSEP changes than EEG

Electrode placement may not be feasible in certain surgeries

Anesthetic interferences (slide 57)

24

SSEP perioperative considerations

Consider TIVA

Analgesia - opioid or ketamine infusion

Any paralysis okay as it amplifies SSEP measurements

Infuse agents/pressors instead of bolusing

1/2 MAC is okay

Use on normotensive and normothermic patients