Neuro Monitoring Flashcards
MEP - Appropriate Measurement
Motor strip surgeries
Spine surgery
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
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
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
MEP vs EMG
EMG is a measurement, MEP is a measured response
MEP - Best Method
Protect ETT from biting Avoid additional MR after intubation Steady infusions, avoid boluses TIVA Realize the pt will move
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
Electromyographic (EMG) - Pathway
Is a local measurement of muscle activity
No pathway exists
EMG - Compatibility/Interference
Volatile - no effect at 1 MAC
NMB - eliminates response
Other - no effect
EMG - Limitations of Measurement
Intrinsic muscle disease or NMJ disease such as myasthenia gravis or polio
EMG - Best Method
Protect ETT from biting
Be cautious of needles
No NMB after intubating dose
NIM EMG - Pathway
Trigeminal… Glossopharyngeal… Internal branch superior laryngeal… Recurrent laryngeal
NIM EMG - Appropriate Measurement
Neck Dissection Thyroidectomy Parathyroidectomy Brainstem surgery Carotid surgery
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
NIM EMG - Compatibility/Interference
NMB - eliminates
Local/topical - decreases
Other - no effect
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
Brainstem Auditory Evoked Potentials (BAEP) - Pathway
Assesses CN VIII (vestibulocochlear aka acoustic nerve through its tract to the pons)
BAEP - Tract Anatomy
Ear stuff
BAEP - Appropriate Measurement
Vestibular nerve
Acoustic neurons
Facial nerve
Cochlear nerve
Acoustic neuroma on vestibulocochlear nerve puts pressure on facial nerve
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)
BAEP - Compatibility/Interference
No effect
BAEP - Best Method
Plain ol anesthesia
Decrease of BAEP is fairly reliable indicator of Stage 4
Visual Evoked Potentials - Pathway
Retina to occipital cortex
Visual Evoked Potentials - Tract Anatomy
Visual cortices
Optic chiasm
Optic nerve
Visual Evoked Potentials - Appropriate Measurement
Craniopharyngiomas
Suprasellar masses
Visual Evoked Potentials - Limitations of Measurement
Very sensitive to any anesthetic technique
Not considered reliable intraoperatively due to high incidence of false positives
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 - ???
Visual Evoked Potentials - Best Method
No established recommendations
Seldom utilized
Avoid hypotension
Avoid high conc of single agent
Facial Nerve Monitoring - Pathway
Facial nerve…
Facial Nerve Monitoring - Tract Anatomy
7th cranial nerve
Brainstem
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)
Facial Nerve Monitoring - Limitations
Exacting needle placement
Can get response from V2 and V3 nerve
Facial Nerve Monitoring - Compatibility/Interference
NMB - eliminates
Dexmedetomidine - none?
Others - none
Facial Nerve Monitoring - Best Method
Protect ETT from biting
No scalp block
Watch for needle displacement
Cortical Mapping - Tract Anatomy
Precentral - Motor cortex “positivity”
Postcentral - Somatosensory cortex “negativity”
Cortical Mapping - Appropriate Measurement
Exact mapping of sensory and motor areas of cerebral cortex
Measures plasticity
Cortical Mapping - Limitations
Placement of electrodes can be difficult
Placement can be impossible of craniotomy window is not aligned with frontal cortex strips
Cortical Mapping - Compatibility/Interference
Volatile/propofol/opiate/NMB - no effect Nitrous - interferes Etomidate/ketamine - enhances Benzos - decreases Dexmedetomidine - unknown
Cortical Mapping - Best Method
Optimize cerebral perfusion
Limit cerebral edema
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
SSEP - Tract Anatomy
Gray matter… White matter…
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
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
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
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
Change in signal
Alert surgeons Review recent changes Assess perfusion Normalize ABG Normalize BP Consider change to technique to enhance
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
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
