IONM Flashcards
The afferent input for somatosensory evoked poten tials (SSEPs) is carried through which spinal cord tract?
A. Spinocerebellar
B. Spinothalamic
C. Dorsal columns
D. Corticospinal
C. Dorsal Columns
Which of the following intravenous anesthetics is con traindicated in patients with intracranial hypertension?
A. Propofol
B. Fentanyl
C. Ketamine
D. All are acceptable
C. Ketamine
A 14-year-old girl with severe scoliosis is to undergo spine surgery. Anesthesia is maintained with fentanyl, N2O 50% in O2, vecuronium, and isoflurane. Neu rologic function of the spinal cord is monitored by SSEPs. In reference to the SSEP waveform, spinal cord ischemia would be manifested as
A. Increased amplitude and increased latency
B. Decreased amplitude and increased latency
C. Decreased amplitude and decreased latency
D. Increased amplitude and decreased latency
B. Decreased amplitude and increased latency
Which of the following is the MOST sensitive means of detecting venous air embolism (VAE)?
A. Electroencephalography (EEG)
B. Pulmonary artery catheter
C. Transesophageal echocardiography
D. Right atrial catheterization
C. Transesophageal echocardiography
Administration of vecuronium during spinal surgery may interfere with monitoring of
A. Dorsal columns
B. Corticospinal tract
C. Electrocorticography
D. Bispectral index
B. Corticospinal tract
A 13-year-old boy is anesthetized with 0.5% isoflu rane, 50% N2O, and fentanyl for scoliosis repair. So matosensory evoked potentials (SSEP) monitoring is conducted during the procedure. Which of the fol lowing structures is NOT involved in conveyance of the stimulus from the posterior tibial nerve to the ce rebral cortex?
A. Corticospinal tract
B. Medial lemniscus
C. Brain stem
D. Internal capsule
A. Corticospinal tract
A 19-year-old woman is undergoing surgery for a Har rington rod placement. General anesthesia is adminis tered with desflurane, nitrous oxide, and fentanyl. After completion of spinal instrumentation, a wake-up test is undertaken. Four thumb twitches are present when the nerve stimulator attached to the ulnar nerve is activated. The volatile anesthetic and nitrous oxide have been dis continued for 10 minutes when the patient is asked to move her hands and feet. After repeated commands, the patient still does not move her hands or feet. The most appropriate intervention at this time would be
A. 3 mg neostigmine plus 0.6 mg glycopyrrolate IV
B. 20μg naloxone IV
C. 0.1 mg flumazenil IV
D. Reduce the distraction on the rods
B. 20μg naloxone IV
Which of the following pharmacologic agents would have the LEAST effect on somatosensory evoked potentials?
A. Isoflurane
B. Nitrous oxide
C. Vecuronium
D. Etomidate
C. Vecuronium
Which of the following pharmacologic agents would have the LEAST effect on transcranial motor evoked potentials (MEPs)?
A. Isoflurane
B. Nitrous oxide
C. Etomidate
D. Fentanyl
D. Fentanyl
Ketamine
A. Decreases cerebral blood flow (CBF)
B. Augments the CO2 responsiveness of the cerebral vasculature
C. Reduces cerebral metabolic rate (CMR)
D. Increases cerebral blood volume (CBV)
D. Increases cerebral blood volume (CBV)
Etomidate does all of the following EXCEPT
A. Abolishes CO2 reactivity
B. Reduces CMRO2
C. Increases both SSEP amplitude and latency
D. Reduces CBF
A. Abolishes CO2 reactivity
What are the evoked potential modalities in IONM?
SSEP (somatosensory evoked potentials)
BAEP (brainstem auditory evoked potentials)
TcMEP (transcranial motor evoked potentials)
VEP (visual evoked potential)
What are the two types of electromyography?
Spontaneous and triggered
What can cause IONM changes intraoperatively?
Iatrogenic injury
surgical maneuvers
ischemia
malpositioning
-anesthetics can mimic this changes
Anesthetic agents work on the nervous system by altering __________ excitability via changes in _________ synaptic function or _________ conduction
Anesthetic agents work on the nervous system by altering neuronal excitability via changes in synaptic function or axonal conduction
More synapses = ___________(more/less) sensitive
More sensitive
The effect an anesthetic has on modality increase with the number of synapses present in the specific pathway being monitored
EEG y-axis records __________?
Voltage
EEG x-axis records _________?
Time
EEG is used to identify what two things?
Decreased CBF states
Intraoperative seizures
What anesthetics are EEG sensitive to?
Potential inhalation agents
Barbiturates
Propofol
Benzos
What is burst suppression useful for?
Neuroprotection when there is a need to reduce CBF (clip) or when CBF is inadvertently reduced (rupture)
What can rule out anesthetic changes to an EEG versus something physiologically significant?
Anesthesia produces global suppression of EEG
Surgical maneuvers, ischemia, and malpositionig produce focal EEG changes (not 100% of the time)
Evoked potentials (EP) stimulate nerves and record from _________ and _________ nervous systems
Stimulate nerves and record from the peripheral and central nervous systems
What is the goal of IONM of evoked potentials?
Monitor response latencies and amplitude for changes from the baseline established early in the procedure
What nerves does SSEP stimulate?
Peripheral nerves in wrist, ankles, body, neck and head
SSEP sends signals through what part of the spinal cord?
Dorsal column medial lemniscus pathway to the brain
For SSEP what should potent inhalational agents be limited to?
0.5-1 MAC
Stability important
N2O _____________ (increases/reduces) SSEP cortical amplitude and _______________ (increases/reduces) latency when used alone or in combination with halogenated agents or opioids.
N2O reduces SSEP cortical amplitude and increases latency when used alone or in combination with halogenated agents or opioids.
What inhalational agent produces more profound changes in cortical SSEPs and MEPs than any other agent?
N2O
N2O is context sensitive and actual effects vary depending on other anesthetic agents already being delivered
Where are transcranial motor evoked potentials (TcMEP) stimulated?
Primary Motor Cortex
Where are TcMEPs recorded from?
Distal extremities (arms, legs, and occasionally the face)
TcMEP latencies reflect the time it takes for the impulses to traverse the what spinal tract?
Corticospinal tract
UE are earlier than LE
When are TcMEPs standardly offered?
Any cervical procedure in a patient with myelopathy or spinal cord injury (trauma)
Any thoracic spine procedure
Any intramedullary spinal cord tumor cases
Any thoracic aortic aneurysm cases (TEVAR)
Any cerebral aneurysm cases
Selective post-fossa/foramen magnum cases
What three things can affect TcMEP?
Blood pressure (low BP)
Temperature (low temp)
Anesthesia (TIVA with no muscle relaxant preferred)
What medication most adversely affects TcMEP?
MUSCLE RELAXANT
Consider Sugammadex if patient does not have 4/4 twitches, avoid redosing
The Corticospinal tract is susceptible to anesthetic agents at what 3 sites?
Motor cortex
Anterior horn cells
Neuromuscular junction
What should you ALWAYS have when doing TcMEP?
SOFT BITE BLOCK
High voltage stimulation of motor cortex required to produce CMAPs in distal extremities produces a strong jaw clench
What is the effect of opioids on SSEPs and TcMEPs
less prominent than with inhalational agents
Produce minimal changes, though some transient depression of amplitude and increase of latency in cortical responses depending on delivery method. Spinal application produces minimal change
Precedex effect on IONM
Good supplement, decreases need for opioids/barbituates/propofol
Can be problematic when >/= 0.5mcg/kg/hr with high propofol rates (creates higher stimulation threshold)
AVOID boluses which can decrease TcMEP amplitude
Ketamine effect on IONM
Enhances cortical SSEP/TcMEP amplitude
Minimal subcortical/peripheral SSEP response
Contraindicated in intracranial pathology due to increased ICP/hallucinations
Avoid boluses when monitoring TcMEP
Etomidate effect on IONM
Increases amplitude of cortical SSEPs and TcMEPs
Increased myoclonus (increased cortical excitability)
Propofol effect on IONM
Induction bolus reduces cortical SSEP/TcMEP amplitude but with rapid recovery
Ideal agent for infusion in conjunction with other TIVA agents to avoid inhaled agents
What is the best anesthetic for SSEP monitoring
Inhalational agent no greater than 1.0 MAC preferred
Muscle relaxant is acceptable (and encouraged)
Notify Neurophysiology when giving bolus of Propofol, narcotic, Ketamine
Prefer no Nitrous Oxide, if needed - less than 50% is typically acceptable case by case basis
Infusions of remifentanil, precedex, and propofol are acceptable
What is the best anesthetic for SSEP/Lower extremity EMG (lumbar fusion)
Inhalational agent no greater than 1.0 MAC preferred
Muscle relaxant can be given at the beginning of the procedure (surgeon will want complete paralysis to last through the exposure part of the procedure)
At least 2/4 twitches are needed to record EMG when requested by Neurophysiology or surgeon (usually during decompression/instrumentation parts of the procedure).
4/4 twitches will be needed to test the pedicle screws
Notify Neurophysiology when giving bolus of Propofol, narcotic, Ketamine
Infusions of remifentanil, precedex, and propofol are acceptable
Prefer no Nitrous Oxide, if needed - less than 50% is typically acceptable case by case basis
What is the best anesthetic method for cranial nerve EMG
Muscle relaxant can often be given at the beginning of the procedure for intubation/positioning (succinylcholine and small doses of rocuronium to get through positioning are typically acceptable)
4/4 twitches are needed to record cranial nerve EMG.
What medication should be avoided completed any case with EMG from the start (thyroidectomy, parotidectomy, XLIF, MVD7)
Non-depolarizing muscle relaxant should not be given at induction or any time during the procedure (succinylcholine is acceptable for intubation)
What is the best anesthetic method for any case with TcMEP?
TIVA strongly preferred (no inhalational agent or Nitrous Oxide) - Remifentanil and propofol best
Precedex infusions should be kept less than 0.5mcg/kg/hr (causes increased threshold of stimulation throughout the case requiring higher and higher stimulation intensity)
Prefer no muscle relaxant to be used, though surgeons sometimes do request muscle relaxant for exposure. No muscle relaxant can be used when actually recording TcMEP (4/4 strong twitches)
Avoid boluses of Propofol or narcotic when TcMEP is being collected frequently
Soft Bite-block required prior to any TcMEP data collection
What anesthetic method is best for any case with EEG?
Inhalational agent no greater than 1.0 MAC preferred
Notify Neurophysiology when giving bolus of
Propofol, narcotics, benzos, or barbiturates
Prefer no Nitrous Oxide, if needed - less than 50% is typically acceptable case by case basis
What anesthetic method is best for VEP?
TIVA strongly preferred (no inhalational agent or Nitrous Oxide) - Remifentanil and propofol best
Propofol should be run at the lowest infusion rate that Anesthesia is comfortable running
Precedex infusions should be kept less than 0.5mcg/kg/hr (can help reduce propofol requirement)
- Rarely used in Intraoperative Neuromonitoring
What IONM does not have any anesthesia restrictions?
BSER (brainstem auditory evoked potentials)
Cheat sheet for how anesthetic agents affect SSEP and MEP
