Intra Operative Neuro Monitoring

Question 1

What is an electroencephalogram used for intraoperatively?

Answer 1

Monitoring and diagnosis of:

• CNS function and ischemia
• Burst suppression
• Depth of anesthesia

Question 2

T/F: A progressive reduction in CBF will produce a reliable pattern change in the EEG

Answer 2

True

Question 3

What are the 3 steps of EEG changes during ischemia?

Answer 3

1. Loss of high frequency activity
2. Loss of power
3. Eventual progression to EEG silence

Question 4

Describe cerebral oximetry

Answer 4

Noninvasive cerebral oxygenation measurement using near-infrared spectroscopy (NIRS) technology

Question 5

When should cerebral oximetry be used intraoperatively?

Answer 5

Any procedure where there may be vascular compromise to the brain from restriction of blood flow or patient positioning

Question 6

What signifies a significant change in cerebral oximetry

Answer 6

• A decrease of 20% from baseline is significant

Question 7

What is a BIS monitor used for?

Answer 7

To measure the depth of anesthesia intraoperatively

Question 8

What is occurring at the following BIS Index Ranges? 0, 20, 40, 60, 80, 100

Answer 8

0 - flat line EEG
20 - Burst suppression
40 - Deep Hypnotic State
60 - General Anesthesia (low probability of explicit recall, unresponsive to verbal stimulus)
80 - Responds to loud commands or mid prodding/shaking
100 - Responds to normal voice

Question 9

What is evoked potential monitoring?

Answer 9

EP modalities detect signals that are the result of specific stimuli applied to the patient

Question 10

What is SSEP?

Answer 10

Somatosensory Evoked Potential

Question 11

What is BAEP?

Answer 11

Brainstem Auditory Evoked Potential

Question 12

What is VEP?

Answer 12

Visual Evoked Potential

Question 13

What is MEP?

Answer 13

Motor Evoked Potential

Question 14

What is the benefit of Evoked Potential Monitoring?

Answer 14

To identify the deterioration of neuronal function, this providing an opportunity to correct offending factors before they are irreversible

Question 15

What are potential offending factors that can that can be identified with EP monitoring? (4)

Answer 15

1. Position of Patient
2. Hypotension
3. Hypothermia
4. Surgical intervention

Question 16

What is monitored with SSEP?

Answer 16

A signal that is detectable on EEG Monitoring the primary somatosensory cortex, and is generated by a CUTANEOUS ELECTRICAL STIMULATION OF A PERIPHERAL SENSORY NERVE, OR A CRANIAL NERVE WITH A SENSORY PATHWAY

Question 17

What 2 things are used to describe SSEP?

Answer 17

1. Polarity - direction of wave deflection

2. Latency - time required for a signal to be detected after a stimulus has been applied

Question 18

What 2 things is SSEP monitoring quantified by?

Answer 18

1. Amplitude of the resulting signal

2. Latency of the resulting signal

Question 19

T/F: Mechanical disruptive changes are more common than ischemic changes for SSEPs?

Answer 19

False - Ischemic change is more common than mechanical disruptive change

Question 20

How is ischemia displayed in SSEP waves?

Answer 20

Causes the amplitude of the signal to decrease the latency of the signal to increase

Question 21

What are clinically significant changes in SSEPs?

Answer 21

• 50% decrease in signal amplitude

- 10% increase in signal latency

Question 22

What does MEP evaluate?

Answer 22

Descending motor pathways

Question 23

What monitoring system complements SSEP monitoring?

What information do the 2 modalities provide?

Answer 23

• Complemented by SSEP, particularly in spine surgeon

- The 2 modalities provide information about the integrity of anatomically different areas of the spinal cord

Question 24

Motor evoked potential stimulus is applied in a ____A___ fashion over the __B__.

Answer 24

A. Transcranial fashion

B. Motor cortex

Question 25

What detects the deflection of MEP stimuli?

Answer 25

Detected by electrodes embedded in the muscle belly

Question 26

How are MEP transcranial electrical stimuli usually delivered? And how is the voltage adjusted?

Answer 26

• Usually delivered as a rapid train of four or more stimuli

- Voltage is then adjusted to achieve adequate signals in both the upper and lower extremities

Question 27

Which generally has more depressant effects on EP monitoring, Inhalation agents or IV agents?

Answer 27

Inhalation agents including nitrous oxide generally have more depressant effects

Question 28

What can have a profound influence on the amplitude & latency of evoked potentials?

Answer 28

Volatile anesthetics

Question 29

What type of MAC is typically kept to avoid quality degradation of evoked potential monitoring?

Answer 29

sub-MAC doses

Question 30

What effects do Propofol and Thiopental have on evoked potentials?

Answer 30

Reduce the amplitude of all modalities of EP, but do not obliterate them

Question 31

What effects do Ketamine and Etomidate on the quality of SSEP?

Answer 31

Reported to enhance the quality of SSEP signals in pts with a weak baseline

Question 32

What effects do opioids, benzodiazepines, and dexmedetomidine have on evoked potentials?

Answer 32

Negligible effects on recording of EP

Question 33

What is the ideal anesthetic for monitoring MEP?

Answer 33

Total IV anesthesia without N2O, because MEPs are extremely sensitive to the depressant effects of inhalation anesthetics including N2O

Question 34

Does MEP monitoring allow for the use of paralytic?

Answer 34

Typically not

Question 35

Why are MEP signals typically obtained intermittently at points during surgery?

Answer 35

MEPs can cause pt movement

Question 36

When is a bite block mandatory?

Answer 36

During transcranial stimulation to prevent injury to the tongue