Neurophysiologic Monitoring

Question 1

An important limitation of transcranial doppler (TCD) results from the fact that most of the examination is done through the temporal bone, which may be thick enough to preclude an adequate examination in …% of patients

Answer 1

10% to 20

Question 2

Some important advantages of trasncranial doppler (TCD) monitoring are that …

Answer 2

it is the only continuous technique that can provide early warning for hyperperfusion and that it detects the number of emboli delivered to the brain during various phases of an operation

Question 3

In the case of the brain, … is believed to measure the degree of oxygen extraction by the brain and to represent the balance between cerebral oxygen supply and demand

Answer 3

jugular bulb venous oxygen saturation (Sjvo2)

Question 4

Normal values of Sjvo2 …

Answer 4

55% to 75%

Question 5

Why does cerebral oximetry determines predominantly “local venous oxygen saturation’?

Answer 5

Because 66% to 80% of the cerebral blood volume is venous blood

Question 6

The normal global pattern changes inthe EEG produced by anesthetic drugs are similar to …

Answer 6

pathologic patterns produced by ischemia or hypoxemia

Question 7

EEG processing for intraoperative monitoring is typically based on
power analysis of a segment of raw EEG over a specific period of
time, referred to as an …

Answer 7

epoch

Question 8

Power analysis uses Fourier transformation to convert the digitized raw EEG signal into component sine waves of identifiable …

The raw EEG data, which is a plot of …, is converted to a plot of …

Answer 8

frequency and amplitude

voltage versus time

frequency and amplitude versus time.

Question 9

Describe the relation between the epoch length and spectral resolution

Answer 9

A longer epoch may produce less epoch-to-epoch variability and allow more precise description of frequency and power. However, the longer epoch increases the delay before new information is processed and displayed, reducing the timeliness of information available for clinical decision-making.

Question 10

Isoflurane, Sevoflurane, Desflurane effects on the EEG with Subanesthetic, anesthetic and Increasing dose >1.5 MAC

Answer 10

• Subanesthetic: Loss of alpha, ↑frontal beta
• Anesthetic: Frontal 4-13 Hz activity
• Increasing dose >1.5 MAC: Diffuse theta and delta → burst suppression → silence

Question 11

Nitrous oxide (alone) effects on the EEG

Answer 11

• Frontal fast oscillatory activity (>30 Hz)
• Reduction of EEG amplitude, especially with inspired concentration >50%
• It doesn’t cause burst supression

Question 12

Etomidate effects on the EEG with low dose, Moderate dose and Increasing high dose

Answer 12

• Low dose: Fast frontal beta activity
• Moderate dose: Frontal alpha frequency spindles
• Increasing high dose: Diffuse delta → burst suppression → silence

Question 13

Propofol effects on the EEG with low dose, Moderate dose and Increasing high dose

Answer 13

• Low dose: Loss of alpha; frontal beta
• Moderate dose: Frontal delta; waxing/waning alpha
• Increasing high dose: Diffuse delta → burst suppression → silence

Question 14

Ketamine effects on the EEG with low dose, Moderate dose and Increasing high dose

Answer 14

• Low dose: Loss of alpha, variability
• Moderate dose: Frontal rhythmic delta
• High dose: Polymorphic delta; some beta
• It doesn’t cause burst supression

Question 15

Opioids effects on the EEG with low dose, Moderate dose and Increasing high dose

Answer 15

• Low dose: Loss of beta; alpha slows
• Moderate dose Diffuse theta, some delta
• High dose: Delta, often synchronized
• It doesn’t cause burst supression

Question 16

Dexmedetomidine effects on the EEG

Answer 16

Moderate slowing, prominent spindles

• It doesn’t cause burst supression

Question 17

Benzodiazepines effects on the EEG with low dose, Increasing high dose

Answer 17

• Low dose: Loss of alpha; increased frontal beta activity
• High dose: Frontally dominant delta and theta
• It doesn’t cause burst supression

Question 18

Evoked potentials of all types (sensory or motor) are described in terms of latency and amplitude. Latency is defined as … of the response. The amplitude is … .

According to convention, deflections below the baseline are labeled … and deflections above the baseline are labeled …

Answer 18

the time measured from the application of the stimulus to the onset or peak (depending on convention used)

simply the voltage of the recorded response

“positive (P),”

“negative (N).”

Question 19

SERs used for intraoperative monitoring include …

Answer 19

somatosensory-evoked potentials (SSEPs , brainstem auditory-evoked potentials (BAEPs), and rarely , visual-evoked potentials (VEPs)

Question 20

Describe the pathway involved in the generation of upper extremity short-latency somatosensory-evoked potentials (SSEPs)

Answer 20

It begin with large-fiber sensory nerves that have their cell bodies in the dorsal root ganglia and central processes that travel rostrally in the ipsilateral posterior
column of the spinal cord. These first-order neurons synapse in the dorsal column nuclei at the cervicomedullary junction. From there, second-order fibers decussate and travel to the contralateral thalamus via the medial lemniscus and third-order fibers project from the thalamus to the frontoparietal sensorimotor cortex

Question 21

Although most evidence indicates that upper extremity evoked potentials are conducted rostrally in the spinal cord through dorsal column pathways, some data suggest that lower extremity SSEPs are conducted at least partially by the …

Stimulation of the posterior tibial nerve or common peroneal nerve at or above motor threshold activates group I fibers that synapse and travel rostrally through the … tract.

After synapsing in nucleus Z at the spinomedullary junction, the pathway decussates and projects onto the …

This pathway difference is important because the … is supplied primarily by the … artery, the artery that also supplies the … as well as neurons in gray matter of the spinal cord

Answer 21

lateral funiculus

dorsal spinocerebellar

ventral posterolateral thalamic nucleus

dorsal lateral funiculus

anterior spinal

descending motor pathway

Question 22

The effects of the currently used volatile anesthetics on cortical SSEPs are …

Answer 22

dose-dependent increases in latency, conduction times and a decrease in amplitude of cortically, but not subcortically, recorded signals

Question 23

Can inhaled anesthetics be used when SSEPs wil be monitored?

Answer 23

In neurologically normal patients, 0.5 to 1 MAC (minimum alveolar concentration) of any of the potent inhaled agents in the presence of nitrous oxide is compatible with monitoring of cortical SSEPs.
Neurologically impaired patients may show a significantly greater sensitivity to inhaled agents, even to the point of not tolerating any recordable level of inhaled agent.

Question 24

Describe the effects of inhaled anesthetics on BAEPs and VEPs

Answer 24

The volatile anesthetics result in increases in latency of BAEPs without significantly affecting the amplitude. Adequate monitoring of BAEPs is possible with any clinically useful concentrations of inhaled agents (with or without nitrous oxide).

Use of the volatile anesthetic drugs during monitoring of VEPs results in dose-dependent increases in latency with or without changes in amplitude. More recent studies report some success in recording intraoperative VEPs from patients with normal eyesight, but waveform variability and potent depression of waveforms by
volatile agents remain problematic

Question 25

NO2 effects on SERs

Answer 25

As with the volatile anesthetics, nitrous oxide causes differing effects on the SERs depending on the sensory system monitored.

It causes decreases in amplitude without significant changes in latency in SSEPs when used alone or when added to a narcotic-based or volatile anesthetic.

The addition of nitrous oxide to a maintenance volatile anesthetic during the monitoring of BAEPs causes no further change. Likewise, use of nitrous oxide alone
causes no change in BAEPs, unless gas accumulates in the middle ear.

Use of nitrous oxide alone results in an increase in latency and a decrease in amplitude in VEPs, but when it is added to a volatile anesthetic technique, it causes no further changes in VEPs

Question 26

Effects of propofol on SSEPs and BEAPs

Answer 26

Propofol may serve as a prototypical example. At typical clinical doses required for general anesthesia, propofol has minimal effects on somatosensory evoked responses recorded along the somatosensory pathway up to the early cortical
potentials.Thus propofol-based anesthetic is frequently used as the preferred technique to optimize signal-to-noise ratio for SSEPs and provide rapid feedback to the surgeon.

BAEPs under propofol anesthesia show minor increases in interpeak latencies and
decreases in amplitude that are insufficient to interfere with clinical monitoring of auditory function

Question 27

Effects of barbiturates on SSEPs and BEAPs

Answer 27

At doses of thiopental far greater than doses producing an isoelectric EEG, adequate monitoring of early cortical and subcortical SSEPs and BAEPs was preserved

Question 28

Ettomidate effects on SERs

Answer 28

After bolus administration and intravenous infusions, etomidate causes increases in latency of all waves and prolongation of central conduction time in SSEPs.

In contrast to virtually all other commonly used anesthetics, etomidate causes increases in amplitude of the cortical SSEP. This effect may be due to an alteration in the balance of inhibitory and excitatory influences or an increase in the irritability of the CNS. This effect seems to be present in the cortex, but not in the spinal cord.

The effects of etomidate on BAEPs are dosedependent increases in latency and decreases in amplitude that are not clinically significant

Question 29

Dexmedetomidine effects on SERs

Answer 29

Based on several case reports and small series, dexmedetomidine is compatible with all types of sensory evoked potential monitoring

Question 30

Opiods effects on SERs

Answer 30

Generally, opioids cause small dose-dependent increases in latency and decreases in amplitude of SSEPs. These changes are not clinically significant.

Effects on amplitude are more variable than the latency increases.

Opioids can be used even in high doses in patients requiring intraoperative SSEP monitoring without impairment of ability to monitor neurologic function adequately.

Opioid-induced changes must be considered, however, when evaluating the recordings. Large intravenous bolus administration of opioids should be avoided at times of potential surgical compromise to neurologic function to prevent confusing the interpretation of SEP changes if they develop.

BAEPs were resistant to doses of fentanyl of 50 mcg/kg with no changes observed in absolute latency, interpeak latency, or amplitude

Question 31

Effects of anesthetics on tcMEPs recorded from muscle are surprisingly profound. This profound effect occurs, because the …

Answer 31

spinal α-motor neuron integrates input not just from the corticospinal tract, but also from propriospinal, cerebellar, and subcortical inputs. These latter inputs are typically inhibitory and thus augmented by anesthetics

Question 32

Anesthetic technique of choice for a surgery tha transcranial motor evoked potencials need to be recorde

Answer 32

Anesthetic techniques typically used by most anesthesiologists for spine surgery would produce prohibitive depression of the MEP. Investigators showed in several studies that intravenous anesthetic drugs produce significantly less depression, and techniques using any of a combination of ketamine, opiates, etomidate, and propofol have been described.

The authors have had excellent experience with a combination of propofol and opiate, which also is supported in the literature. There is also support for the use of ketamine and lidocaine.

One study demonstrated significant attenuation of tcMEPs during scoliosis surgery when dexmedetomidine was used as an adjunct to propofol and remifentanil.

The use of neuromuscular blocking agents during tcMEP recording is typically not advised.

Question 33

Anesthetic management of Seizure Surgery

Answer 33

To provide good conditions during the electrocorticography
recording, the level of anesthesia is lightened (e.g., by use of a strict nitrous oxide–narcotic technique or low concentrations of volatile anesthetic drugs).

Provocative techniques, such as hyperventilation or administration of a small dose of methohexital, may be useful to activate the seizure focus.

Question 34

Anesthetic considerations of awake craniotomies

Answer 34

Such procedures are typically divided into exposure, mapping, and
resection phases, and can be done with the patient entirely awake or
awake only during periods when the neurologic examination must be
assessed.

Common to all these approaches is the need for:
- Meticulous locoregional anesthesia of the scalp at the craniotomy site and the pin sites of the head holder;
- A patient who is well informed about the awake parts of the procedure and is willing and able to cooperate.

Dexmedetomidine, propofol, and remifentanil are the agents most frequently incorporated into the anesthetic regimens for awake craniotomy. Complications of awake craniotomy include nausea, vomiting, respiratory problems, and “tight” brain, but are typically mild and occur in less than 10% of cases in experienced centers.

Question 35

During seizure surgery, seizures triggered by cortical stimulation can be stopped by …

Answer 35

the application of iced saline to the exposed cortex or a small amount of barbiturate or propofol

Question 36

What is the most common tumor located in the cerebellopontine angle?

Answer 36

Vestibular nerve schwannoma

Question 37

Because of the common origin of the … and the essentially identical intracranial trajectory of the …, … are concerns during surgical resection of Vestibular nerve schwannoma

Answer 37

cochlear component of cranial nerve VIII

facial nerve

hearing loss and facial nerve palsy

Question 38

Prospective trials have shown a higher percentage of patients with a functional facial nerve 1 year after surgery if facial nerve monitoring is used. … on EMG warn of impending damage caused by stretch or compression. Once again, it is important to remember that … may elicit no EMG discharge, and … may eliminate the ability to monitor EMG completely

Answer 38

Neurotonic discharges

sharp section of the nerve

neuromuscular blockade

Question 39

Normal CBF in gray and white matter averages …

With most anesthetic techniques, the EEG begins to become abnormal when CBF decreases to …

Cellular survival is not threatened until CBF decreases to …

Answer 39

50 mL/100 g/min

20 mL/100 g/min

12 mL/100 g/min

Question 40

Are neurologic monitoring indicated for surgeries with cardiopulmonary bypass?

Answer 40

Based on current information, no neurologic monitoring techniques, either alone or in combination, are clearly useful in improving outcome during surgical procedures requiring CPB. That said, processed EEG and NIRS are both noninvasive and comparatively simple to interpret, while providing information not
otherwise obtainable during CPB. They can be usefully integrated into the armamentarium of the cardiac anesthesiologist. Whether dedicated neuromonitoring personnel and further techniques add
meaningfully beyond that is at present unclear

Question 41

Particularities of SSEPs monitoring in children

Answer 41

• Prolonged Erb’s to cortical or cervical to cortical inter-peak latency. Difficult to obtain; low amplitude
• Incomplete myelination of medial lemniscus and thalamocortical pathways. Incomplete myelination of dorsal columns; asynchronous volleys
• Avoid volatile anesthetic drugs, avoid burst suppression, reduce stimulation rate. As above, increase pulse length; optimize signal:noise ratio

Question 42

Particularities of tcMEP monitoring in children

Answer 42

• Cortical and spinal cord motor neurons very susceptible to effects of volatile agents. Variance in conduction velocity of large CST fibers exceeds mean conduction velocity
• TIVA, may need low-dose ketamine to help support BP. Double-train stimulation with unequal train lengths; optimizing inter-train interval

Question 43

Particularities of BAEPs in children

Answer 43

• Low quality signals with volatile agents
• TIVA for ABR for less than 24 months

Question 44

A example of a procedure commonly performed only in children is infant/toddler hearing exams by
administering auditory brainstem response tests under anesthesia. Recently, a study reported that anesthesia with … was more likely to lead to a false-positive diagnosis of hearing loss and exaggerate the severity of hearing loss compared to a …

Answer 44

Sevoflurane

propofol infusion

Question 45

Complete EEG suppression usually develops at …°C

Answer 45

15°C to 18

Question 46

Hypocapnia effects on EEG

Answer 46

is known to activate excitable seizure foci and in rare cases may produce EEG evidence of cerebral ischemia even in awake patients

Question 47

Hypercapnia effects on the EEG

Answer 47

Hypercapnia, unless severe and associated with hypoxemia, has only indirect effects secondary to increased CBF. In
an anesthetized patient, hypercarbia-associated increases in CBF may have similar effects to the effects seen with increasing end-tidal tension of volatile anesthetics

Question 48

Decreases in mean arterial blood pressure to below levels of cerebral autoregulation lead to progressive changes in SERs. Describe then

Answer 48

SSEP changes observed in this scenario are progressive decreases in amplitude until loss of the waveform
with no changes in latency.

BAEPs are resistant to even profound levels of hypotension (mean arterial pressure of 20 mm Hg in dogs).

Cortical SERs, which are produced as a result of multiple synaptic transmissions, seem to be more sensitive to hypoperfusion than SERs produced by the spinal cord, brainstem, or non-synaptic transmission

Question 49

Changes in temperature also affect SERs. Describe it.

Answer 49

Hypothermia causes increases in latency and decreases in amplitude of cortical and subcortical SERs after all types of stimulation.

Hyperthermia also alters SERs, with increases in temperature leading to decreases in amplitude in SSEPs and loss of SSEPs at 42°C during induced hyperthermia

Question 50

When motor evoked potentials are utilized, which anesthetic technique is commonly implemented?

Answer 50

total intravenous anesthesia (TIVA) without the use of NMBA is commonly implemented

Question 51

When intraoperative neurophysiological monitoring is necessary, … use may improve the quality of evoked potentials and are often used as adjuncts to propofol infusions.
… use has been described in addition to propofol infusions without significantly affecting SSEPs, but its effects on motor evoked potentials have been mixed.

Answer 51

Ketamine and etomidate

Dexmedetomidine

Question 52

Describe the Current Practices in Neurologic Monitoring for:
Carotid endarterectomy
Scoliosis surgical treatment
Acoustic neuroma
Intracranial aneurysm clipping
Cranial nerve V decompression
Cranial nerve VII decompression
Supratentorial mass lesions
Infratentorial mass lesions
Decompression of spinal stenosis
Spinal cord trauma
Cardiopulmonary bypass
Aortic coarctation
Aortic aneurysm repair

Answer 52

1) Carotid endarterectomy:
- Awake patient neurologic examination, EEG, SSEP, TCD: National Institutes of Health (NIH) recommends use of one of these four available monitors;
- cerebral oximetry (CO): Threshold value not determined, inadequate normative population data

2) Scoliosis surgical treatment:
- SSEP: Monitoring recommended and may substitute for wake-up testing
- Wake-up test: Largely abandoned in centers using electrophysiologic monitoring; monitoring is not continuous, and false-negative monitoring patterns reported
- MEP: Increased clinical use now that transcranial electrical stimulation is FDA approved; useful in combination with SSEP

3) Acoustic neuroma
- Facial nerve monitor: Facial nerve monitoring recommended
- BAEP: BAEP showing some clinical evidence of improved outcome in some procedures

4) Intracranial aneurysm clipping:
- SSEP, EEG, tcMEP: Used routinely in some centers; limited clinical data on outcome, but appears clinically useful during anterior circulation procedures

5) Cranial nerve V decompression:
BAEP: Used in some centers; reduces hearing loss

6) Cranial nerve VII decompression:
- BAEP, facial nerve monitor: Data from small series showing improved hearing preservation

7) Supratentorial mass lesions:
- SSEP, tcMEP: Used in some centers in selected high-risk procedures

8) Infratentorial mass lesions:
- BAEP, SSEP, tcMEP: BAEP to detect retractor-related cranial nerve VIII injury; SSEP and tcMEP in rare, high-risk lesions adjacent to ascending sensory or descending motor pathways

9) Decompression of spinal stenosis:
- SSEP, tcMEP: Used in some centers in high-risk procedures (more often cervical)

10) Spinal cord trauma:
- SSEP, MEP: Used in some centers in high-risk procedures

11) Cardiopulmonary bypass:
- EEG, TCD, Sjvo2, CO: Used routinely in some centers; actively studied, but no outcome data yet

12) Aortic coarctation:
- SSEP :Used routinely in a few centers; no widespread acceptance

13) Aortic aneurysm repair:
- SSEP, MEP: Used routinely in a few centers; no widespread acceptance