Neuro Monitoring

Question 1

Over-riding principles for neurophysiologic monitoring

Answer 1

• 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!

Question 2

MEP description

Answer 2

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

Question 3

MEP limitations

Answer 3

Anesthetic interference

Difficulty in baseline establishment due to NMB, positioning, electrocautery

Pathologies such as MS can interfere

Question 4

MEP interference from anesthetics (limitations)

Answer 4

slide 12

Question 5

MEP considerations

Answer 5

• 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

Question 6

EMG (electromyographic)

Answer 6

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

Can be used to confirm integrity of hardware placement,

Question 7

Differences between EMG an MEP:

Answer 7

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

Question 8

EMG limitations

Answer 8

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

Question 9

NIM-EMG method

Answer 9

• 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

Question 10

NIM indications

Answer 10

Neck Dissection
Thyroidectomy
Parathyroidectomy
Brainstem Surgery
Carotid Surgery

Question 11

NIM limitations

Answer 11

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)

Question 12

NIM-EMG considerations

Answer 12

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

Question 13

BAEP (brainstem auditory evoked potentials) assesses..

Answer 13

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

Question 14

Limitations to BAEP

Answer 14

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

Question 15

BAEP uses

Answer 15

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)

Question 16

Visual Evoked Potentials

Answer 16

• Rarely done
• Used to assess the optic nerve
• Almost everything interferes with it (slide 39)

Question 17

Facial nerve monitoring - what does it monitor?

Answer 17

Monitors the various endpoints of CN VII (facial nerve)

Question 18

When should facial nerve monitoring be used?

Answer 18

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)

Question 19

Limitations of facial nerve monitoring

Answer 19

Needle placement needs to be exact

Tongue and ETT really needs to be protected in this situation

Question 20

Cortical mapping limitations

Answer 20

N2O, Versed (benzos)

Craniotomy window needs to be aligned with frontal cortex strips

Question 21

SSEP (somatosensory evoked potentials) pathway

Answer 21

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

Question 22

SSEP indications

Answer 22

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

Question 23

SSEP limitations

Answer 23

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)

Question 24

SSEP perioperative considerations

Answer 24

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