Neuro Monitoring Flashcards
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!
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
MEP limitations
Anesthetic interference
Difficulty in baseline establishment due to NMB, positioning, electrocautery
Pathologies such as MS can interfere
MEP interference from anesthetics (limitations)
slide 12
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
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,
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
EMG limitations
Intrinsic muscle diseases (myesthenia gravis, polio, etc..) and NMB
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
NIM indications
Neck Dissection Thyroidectomy Parathyroidectomy Brainstem Surgery Carotid Surgery
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)
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
BAEP (brainstem auditory evoked potentials) assesses..
CN VIII (vestibulocochlear nerve) through its tract to the Pons
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
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)
Visual Evoked Potentials
- Rarely done
- Used to assess the optic nerve
- Almost everything interferes with it (slide 39)
Facial nerve monitoring - what does it monitor?
Monitors the various endpoints of CN VII (facial nerve)
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)
Limitations of facial nerve monitoring
Needle placement needs to be exact
Tongue and ETT really needs to be protected in this situation
Cortical mapping limitations
N2O, Versed (benzos)
Craniotomy window needs to be aligned with frontal cortex strips
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
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
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)
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
