Neurophysiology (Ding)

Question 1

What arteries supply the blood flow to the normal brain?

Answer 1

Two carotid arteries (L/R) and two vertebral arteries (More posterior L/R)

Question 2

What provides collateral circulation in the brain?

Answer 2

Circle of Willis

Question 3

At what level of the spine do the carotid arteries bifurcate into the external and internal carotid arteries?

Answer 3

C3

Question 4

Describe the bifurcations of the internal carotid artery into the cerebral circulation.

Answer 4

Internal carotid artery give rise to 7 branches

It ultimately bifurcates into the anterior and middle cerebral arteries

Together, the anterior+middle cerebral arteries define the anterior cerebral circulation.

Question 5

Which arteries supply the spinal cord and what parts of the spinal cord do they perfuse?

Answer 5

Anterior spinal arteries (2): anterior 2/3 of spinal cord

Artery of Adamkiewicz: thracolumbar cord (joins the anterior spinal artery in the lower thoracic)

Posterior spinal arteries (2): posterior 1/3 of spinal cord

Question 6

Describe the flow of CSF.

Answer 6

Lateral ventricles –> interventricular foramina (of Monro) –> third ventricles –> cerebral aqueduct of Slyvius –> fourth ventricle –> spinal cord –> arachnoid granulations –> absorption via dural venous sinuses

Question 7

How much CSF volume exists at anyone time? How much is produced in a 24 hour period?

Answer 7

150 mL at any one time

> 450 mL / day

Question 8

What is the function of the CSF?

Answer 8

Cushions the brain

Maintains brain function by regulating pH and electrolytes

Carries away waste products and delivers nutrients

Question 9

How does cerebral blood flow respond to changes in PaCO2?

Answer 9

As arterial CO2 increases from 25 mm Hg to 65 mm Hg, cerebral blood low increases in a linear fashion.

Question 10

How can hyperventilation be used as a therapy in the context of a patient’s neurology?

Answer 10

It can be used for short periods of time to relax the brain or decrease ICP.

Question 11

How long does hyperventilation therapy last in decreasing ICP and why?

Answer 11

Hyperventilation will only decrease ICP for 4-6 hours.

After this time period, the body’s compensates for it (metabolic compensation to hyperventilation) and ICP goes back up.

Question 12

Early hyperventilation in traumatic brain injury is associated with poor/good outcomes. (Choose one)

Answer 12

Poor

Question 13

Describe CBF relationship with changes in PaO2.

Answer 13

CBF response to changes in PaO2 is flat until PaO2 falls < 50 mm Hg (then it rises quickly)

Question 14

CBF is maintained between CPP of __ to __ mm Hg.

Answer 14

60-160

Question 15

What is the difference between communicating and obstructive hydrocephalus?

Answer 15

Communicating hydrocephalus: failure to absorb CSF (typically due to dysfunctional arachnoid granulations); evolves over years and characterized by barely perceptional changes

Acute hydrocephalus: direct obstruction or compression of a CSF passageway; rapid progression that may require external ventricular drainage

Question 16

What are the effects of inhalational anesthetics on CBF and metabolism?

Answer 16

(Dose dependent effects)

0. 5 MAC: CMR suppression > vasodilation (decreased CBF)
1. 0 MAP: CMR suppression = vasodilation (CBF unchanged)

>1.0 MAC: vasodilation > CMR suppression (significantly increased CBF)

Question 17

What is the effect of N2O on ICP and CBF?

Answer 17

it increases both.

Question 18

What is the effect of most of our IV anesthetic agents on CBF amd CMR?

Answer 18

Mostly decreases or does nothing to either EXCEPT for ketamine which increases CMR significantly.

Question 19

What information does EEG give us?

Answer 19

Ischemia

Seizures

Burt-suppression pattern

Functional assessment

Depth of anesthesia

Question 20

Indications for EEG include..

Answer 20

Carotid endarterectomy

Bypass

Cerebrovascular surgeries

Burst suppression necessary for cerebral protection

ICU

Suspected seizures

Question 21

EEG frequencies + names and their meanings.

Answer 21

Delta 0-3 Hz (deep anesthesia or coma)

Theta 4-7 Hz (transition to deep anesthesia)

Alpha 8-12 Hz (light anesthesia/relaxation)

Beta >12 Hz (awake)

Question 22

What is burst suppression and what are the indications for it?

Answer 22

Burst supression: periods of normal brain activity interrupted by stretches of greatly reduced activity >10 seconds

Indications:

Refractory high ICP

Refractory epilepsy

Intra-op neuroprotection

Cerebral vascular surgeries

Question 23

What can we do to induce burst suppression?

Answer 23

Deep anesthesia with anesthetic agents (esp. propofol, barbs, benzos, isoflurane)

Deep hypothermia

Question 24

In BIS monitors what is the proposed optimal range to prevent intra op awareness?

Answer 24

40-60

Question 25

In SSEP monitoring, what changes are considered clinically significant?

Answer 25

50% decrease in signal amplitude 10% increase in signal latency

Question 26

What anestheic agents can depress SSEPs? Which ones can enhance it?

Answer 26

Volatiles including N2O Opioids (large boluses) BUT can be enhanced by ketamine and Precedex

Question 27

Which cranial nerve is monitored through BAEPs?

Answer 27

CNVIII | (brainstem auditory evoked potential)

Question 28

What anesthetics effect MEPs?

Answer 28

Volatiles (more sensitive than SSEPs) NMBs

Question 29

What is the Transcranial Doppler? What are its indications?

Answer 29

Noninvasive monitor that evalutes relative flow changes through the large basal arteries of the brain. Indications: Suspected emboli (esp in TBI/traumatic brain injury) Bypass Vasospasm evaluation Need for noninvasive ICP measurement

Question 30

Indications for ICP monitoring...

Answer 30

All severe TBI/traumatic brain injuries (GCS \< 9) with abnormal CT scans Severe TBI in which pt is \> 40 y/o, is posturing, or has SBP \< 90

Question 31

Ways to decrease ICP

Answer 31

30 degrees of head up (positioning) Decrease CMR (anesthetics) CSF drainage Lasix Hyperventilation

Question 32

How can we provide cerebral protection?

Answer 32

Hypothermia (35-36C for mild ischemic risk; 33-35C for planned period of focal ischemia; \<20C for prolonged cardiac arrest) Volatiles (esp isoflurane) Propofol Barbiturates (esp thiopental) Euglycemia (controversial)