Obj. 12-17

Question 0

What is the preferred method of anesthesia with Evoked Potentials?

Answer 0

Narcotics-they cause little change

Question 1

In what order are Evoked Potentials adversely affected by anesthetic agents? (greatest to least)

Answer 1

VEP > SSEP/MEP > BAEP

Question 2

What are Visual Evoked Responses used for?

Answer 2

Visual Evoked Responses:

• evaluate the optic nerve
• used for tumor surgery that may effect the optic chiasm, pituitary or anterior cerebral vasculature

Question 3

What are Brainstem Auditory Evoked Responses used for?

Answer 3

Brainstem Auditory Evoked Responses:

• monitor the function of the auditory pathway between CN VIII and the brainstem and cortex
• Used in pts with increased risk for brain injury during intracranial surgery

Question 4

What are Motor Evoked Potentials used for?

Answer 4

Motor Evoked Potentials:

-monitor ischemia in the anterior (ventral) columns by stimulating the motor cortex to elicit movement

Question 5

How do IV and inhalational agents effect Motor Evoked Potentials?

Answer 5

Motor Evoked Potentials:

• are very sensitive to anesthetics (particularly VAs. N2O is < depressing than equivalent MACs of other VAs)
• TIVA works well: narcotics, propofol. Propofol causes MEP suppression, but < than VAs
• NDMR weaken MEPs! (Avoid during critical parts of surgery)

Question 6

What are Somatosensory Evoked Potentials (SSEPs) used for?

Answer 6

SSEPs:

• monitor sensory pathways (DORSAL COLUMN, brainstem, subcortex, and sensory cortex). Used during spine surgery& intracranial vascular surgery
• the response of peripheral nerve stimulation to CONTRALATERAL somatosensory cortex
• SSEPs are derived from EEG waves, just significantly less.

Question 7

How do IV and inhalational agents effect SSEPs?

Answer 7

• All VAs:dose-dependent increase in SSEP latency/decrease in amplitude
• Adding N2O potentiates these responses of VAs & IV AGENTS (fentanyl) when used with GA, but N2O alone effects SSEPs LESS than equivalent MAC levels of gases
• NDMRs do not hinder SSEPs & may improve waveform quality

Question 8

Which two IV agents dramatically increase ampitude?

Answer 8

Etomidate & Ketamine

Question 9

What is the suggestion for titration of VAs with any mode of Evoked Potentials?

Answer 9

Use < .5 MAC (.5-1) & avoid rapid changes in anesthetic depth (Find a good plane & keep them there!)

Question 10

What is Electromyography (EMG) used for?

Answer 10

EMG:

• assesses cranial and peripheral motor nerves with electrodes placed into or near specific muscles
• used during spine surgery or to look at specific cranial nerves

Question 11

How do IV and inhalational agents effect EMGs?

Answer 11

• VAs do not affect EMGs

- AVOID MUSCLE RELAXANTS

Question 12

What are the indications for cerebral oximetry monitoring?

Answer 12

• mostly used in CEAs
• intracranial surgery where a change in the patient’s neuro status may occur
• shoulder surgeries and other sitting cases

Question 13

How is cerebral oximetry used to monitor the neurosurgical patient?

Answer 13

• Obtain baseline cerebral oximetry reading pre-induction
• Monitor and keep it within 20% of baseline (more than that correlates with a change in neuro status)
• Notify surgeon of sudden, drastic changes. Benefits are controversial.

Question 14

How should fluids be managed in neurosurgery?

Answer 14

• AVOID glucose-containing solutions
• Keep the pt ISOvolemic, ISOtonic, & ISOoncotic. If dehydrated, restore volume
• Give hourly maintenance & replace U/O
• Replace blood when Hct 25-30% (depending on status & hx)
• Mannitol may be given after the dura is opened

Question 15

Discuss positioning in neurosurgery (in general).

Answer 15

• Most common: supine, semi-sitting, lateral & prone
• 100%O2 prior to turn & remember to reconnect all monitors!
• Watch for hypoTN with sicker pts. Possibly turn agent down/off

Question 16

If neurosurgery in the supine position, use caution to…

Answer 16

Avoid extreme head rotation that can obstruct jugulars or vertebrals

Question 17

If neurosurgery in the prone position, one should…

Answer 17

• watch eyes for risk of BLINDNESS

- Check ALL pressure points

Question 18

What are the relative contraindications to the sitting position?

Answer 18

• pt with ventriculo-atrial shunt
• an awake, un-anesthetized pt demonstrating cerebral ischemia in the upright pstn (cerebral vascular dx, coronary dx)
• CAD with CHF with Right atrial P> Left atrial P, or patent foramen ovale

Question 19

What are the complications of sitting pstn?

Answer 19

• Circulatory instability
• VAE
• Quadriplegia
• Head, neck, and tongue edema
• Compressive peripheral neuropathy

Question 20

How is ventilation managed during neurosurgery?

Answer 20

• Obtain baseline ABG to aproximate PaCO2 with etCO2 readings
• Routine hyperventilation is NO LONGER recommended
• Maintain PaCO2 30-32 mmHg

Question 21

Which drugs treat “tight brain?”

Answer 21

• Boluses or transfusions of thiopental, etomidate, propofol, or narcotic
• Diuretics

Question 22

What is the most sensitive NON-invasive monitor for VAE?

Answer 22

Precordial Doppler (still a standard modality)

Question 23

What are the anesthetic implications of stereotactic -assisted procedures?

Answer 23

• Pts are often sedated & local anesthesia is used to apply the localizing frame
• Sedation is omitted if IICP or altered LOC
• Awake FOB may be safest, intubation is hard with frame in place
• Avoid hypocapnea during GA to prevent shifting of the brain

Question 24

What are the anesthetic implications for endovascular procedures?

Answer 24

• Typically off-site, GA
• Make sure ventriculostomy bag stays level, doesn’t overflow, & stays open (per surgeon request)
• Keep lines on pt’s left side, out of the way of rotating fluoroscopy heads
• maintain etCO2 30-32 to prevent vasospasm, keep paralyzed, maintain BP within 20% of baseline
• Heparanize to ACT of 200 secs if coiling, 300 secs for stents
• If CTscan, keep paralyzed and run penthothal gtt if ordered

Question 25

What are some vasospastic techniques?

Answer 25

• Keep MAP >75, normal etCO2
• 3 H’s: Hypervolemia, Hypertonic, Hyperoncotic (modify fluids for pt tolerance)
• Nicardipine gtt: Mix 50mg/250ml, run at 0.5-2.2mg/hr. Increase to 5-15mg/hr for acute hypertensive crisis
• Nicardipine increases ICP by increasing CBF & decreased CPP

Question 26

What can we do to prevent vision loss associated with prone and sitting cases?

Answer 26

• use Foam headrests, check eyes (& document) at least every 20 mins, ProneView Mirror
• Head neutral in relation to the back
• Keep SBP w/in 20% of baseline, pressors PRN
• Avoid head-down pstng, Reverse Trendelenburg if possible
• Mayfield head clamp avoids compression of the globe

Question 27

What are the mechanisms of vision loss associated with prone & sitting cases?

Answer 27

Ischemic Optic Neuropathy (ION)-Most common.
-Possible causes: Low BP; Blood loss, anemia, or hemodilution; increased intraocular pressure; abnormal autoregulation of the optic nerve circulation; vasopressors, systemic vascular disease
Central retinal artery occlusion-Less common. d/t diret compression in spine surgery

Question 28

Identify the pathophysiology of an aneurysm.

Answer 28

Aneurysm is caused by an abnormal, localized dilation of the intracranial arteries.

Question 29

Identify the pathophysiology of SAH.

Answer 29

• A bleed between the pia and arachnoid layers

- Most common cause: rupture of cerebral aneurysm

Question 30

Identify the pathophysiology related to AVMs.

Answer 30

Similar to aneurysms. A “tangling” of thin-walled abnormal vessels without an intervening capillary bed.
-Congenital disorder. Arteries fow directly into veins

Question 31

Identify the pathophysiology of carotid atherosclerosis.

Answer 31

Vascular plaques eventually occlude or rupture the vascular lumen in the internal carotid artery