Mod IX: Neuro Monitoring

Question 1

_{Neuro Monitoring}

A sensory stimulus triggers an afferent nerve impulse that can be detected by surface electrodes placed by a technician

Answer 1

Sensory evoked potentials (SEPs)

Signal averaging is required to extract the evoked potentials from background noise

Question 2

_{Neuro Monitoring}

Three types of SEPs are used clinically

Answer 2

Somatosensory (SSEP)

^{[most common]}

Visual (VEP)

Auditory (BAEP) (Brainstem Auditory)

Question 3

_{Neuro Monitoring}

Somatosensory (SSEP)

Answer 3

Clinical studies utilize electrical stimulation of peripheral nerves, which gives larger and more robust responses

The stimulation sites typically used for clinical diagnostic SSEP studies are the median nerve at the wrist, the common peroneal nerve at the knee, and/or the posterior tibial nerve at the ankle

Recording electrodes are placed over the scalp, the spine, and peripheral nerves proximal to the stimulation site

Question 4

_{Neuro Monitoring}

Visual (VEP)

Answer 4

Tests the function of the visual pathway from the retina to the occipital cortex

It measures the conduction of the visual pathways from the optic nerve, optic chiasm, and optic radiations to the occipital cortex.

Not used in OR that much

Question 5

_{Neuro Monitoring​}

Auditory (BAEP) (Brainstem Auditory)

Answer 5

Very small electrical voltage potentials originating from the brain recorded from the scalp in response to an auditory stimulus

Used on a small percentage of pts that are coming in for hearing test

Not usually a/w neuro procedures

Test Brainstem Auditory responses

Question 6

_{Neuro Monitoring​ - Sensory evoked potentials (SEPs)}

Anesthetic considerations - SSEPs - What % 50% in amplitude from baseline in response to a specific surgical maneuver is considered to be a significant change warranting action to avoid potential danger?

Answer 6

A reduction of 50% in amplitude from baseline in response to a specific surgical maneuver is considered to be a significant change warranting action to avoid potential danger

If there is a reduction of 50% in amplitude from baseline when the surgeon is working in a specific area, this means that what they are doing in that area could potentially lead to irreversible sensory deficit

So they should stop working in that area if possible and move to a different area

Question 7

_{Neuro Monitoring​ - Sensory evoked potentials (SEPs)}

Anesthetic considerations - BAEPs - Which increase in latency is clinically significant?

Answer 7

Increased latency of more than 1 millisecond is clinically significant

Question 8

_{Neuro Monitoring​ - Sensory evoked potentials (SEPs)}

Anesthetic considerations - All anesthetics influence evoked potentials to some extent - How do Inhalation agents influence evoked potentials?

Answer 8

Inhalation agents cause a dose dependent increase in latency and decrease in amplitude in cortical SSEPs and VEPs

N2O with inhalation agents has a profound effect

Do not use if possible

Question 9

_{Neuro Monitoring​ - Sensory evoked potentials (SEPs)}

Anesthetic considerations - Effect of IV agents on SSEPs

Answer 9

SSEPs are less sensitive to IV agents

Opioids have little effects

Dexmedetomidine & clonidine (a-2 receptor agonists) have little effect

Ketamine and etomidate enhance

Question 10

_{Neuro Monitoring​ - Sensory evoked potentials (SEPs)}

Anesthetic considerations - Effect of anesthetic agents on BAEPs

Answer 10

BAEPs resist the influence of anesthetic agents

Can use standard GETA

Question 11

_{Neuro Monitoring​ - Sensory evoked potentials (SEPs)}

Anesthetic considerations - What’s the appropriate management of inhalation agents or IV agents while SEPs are used?

Answer 11

Must maintain constant drug levels (no big bolus or rapid ↑in inhalation agent or IV agents)

Low dose inhalation (<0.5 MAC) combined with propofol and narcotic infusions (Remifentanil my choice) works well

Question 12

_{Neuro Monitoring​ - Sensory evoked potentials (SEPs)}

Anesthetic considerations - Physiologic factors that can alter SEPs readings include:

Answer 12

↑↓Temp

Changes in PaO2 and PaCO2

In addition Fluids used to irrigate the brain or spinal cord can cause marked changes

Question 13

_{Neuro Monitoring​ - Motor evoked potentials (MEPs)}

How are Motor evoked potentials (MEPs) produced?

Answer 13

Direct (epidural) or indirect (transosseous) stimulation of the brain or spinal cord

Can be electrical or magnetic

Following transcranial stimulation (brief high voltage pulses via scalp electrodes), a signal descends through the dorsolateral & ventral spinal cord

Question 14

_{Neuro Monitoring​ - Motor evoked potentials (MEPs)}

Beacuse Motor evoked potentials (MEPs) can be recorded from the spinal cord (epidural space), peripheral nerve, or muscle using EMG and evoked potential averaging techniques, they can

Answer 14

Elicits contralateral responses

Cause seizures

(do not use if seizure history)

Skull fracture can lead to neural damage due to focusing impulse to a region

Pacemakers and CVP or PA caths should not have MEP monitoring!!!

Question 15

_{Neuro Monitoring​ - Motor evoked potentials (MEPs)}

Indications for Motor evoked potentials (MEPs) monitoring

Answer 15

Intramedullary tumor resection

with Risk of corticospinal tract damage

Scoliosis surgery

No need for wake-up test

Continuous (intermittent) monitoring throughout

Cerebrovascular procedures & cerebral tumor resection

AAA surgery

Detect ventral horn ischemia

Question 16

_{Neuro Monitoring​ - Motor evoked potentials (MEPs)}

Motor evoked potentials (MEPs) are done in conjunction with

Answer 16

SSEPs

Although you could see SEPs without MEPs

Question 17

_{Neuro Monitoring​ - Motor evoked potentials (MEPs)}

Why would you Usually need less than 0.3 MAC when using Motor evoked potentials (MEPs)\

Answer 17

Motor evoked potentials (MEPs) are Extremely sensitive to anesthetics

Inhalation agents are their powerful depressants

Usually need less than 0.3 MAC

N2O less suppressive to MEPs than other inhalation agents

If doing SSEPs (almost always) can not use N2O

Question 18

_{Neuro Monitoring​ - Motor evoked potentials (MEPs)}

What’s ther effect of major classes of anesthetic drugs, temp, O2sat and BP on Motor evoked potentials (MEPs) monitoring?

Answer 18

Benzodiazepines, barbiturates, and propofol depress myogenic MEPs

Narcotics, etomidate, and ketamine have little to no effect

NMBs affect EMG by depressing myoneural transmission

Hypothermia, hypoxia, and hypotension will alter recordings

Question 19

_{Neuro Monitoring}

Why is it important to monitor doses of anaything while doing Neuro Monitoring?

Answer 19

High dose anything interferes with monitoring