Anesthesia of Patients with CNS Disease

Question 1

What is the Monro-Kellie doctrine?

Answer 1

Cranium has a fixed volume:
10% blood
10% CSF
80% parenchymal tissue

An increase in any component must cause a decrease in another or an increase in ICP will occur

Question 2

What is the Cushing Reflex?

Answer 2

A physiologic response to increased ICP characterized by systemic hypertension and profound brady cardia

Question 3

What can influence intracranial pressure?

Answer 3

Cerebral blood flow
Cerebral metabolic rate
Anesthetic drugs
Hypoventilation

Question 4

How do GABA agonists affect CBF and ICP?

Answer 4

Relatively unchanged CBF and ICP

Question 5

How do inhaled anesthetics affect CBF and ICP?

Answer 5

Increase CBF and ICP

Question 6

How do alpha-2 agonists affect CBF and ICP?

Answer 6

Minimal effect on CBF and ICP

Question 7

How do phenothiazines affect CBF and ICP?

Answer 7

Have little effect on CBF and ICP

Question 8

How do opioids affect CBF and ICP?

Answer 8

CBF and ICP relatively unchanged

Question 9

How do cyclohexamines affect CBF and ICP?

Answer 9

Increase CBF and ICP

Question 10

Does acepromazine cause or facilitate seizures? Why or why not?

Answer 10

Controversy exists regarding the use of acepromazine in animal with a history of seizures
There is no evidence that acepromazine actually decreases seizure threshold

Question 11

What is the relationship between PaCO2, CBF, and ICP?

Answer 11

CBF varies directly and linearly with PaCO2 because cerebral vascular resistance varies inversely with PaCO2
CBF and ICP are linearly related, so an increase in CBF will have an increase in ICP
ICOO can increase during anesthesia largely due to alterations in CBF
So, they are all linearly related and if one increase, so will the others

Question 12

Is management of increased ICP likely with thoracolumbar disk protrusion?

Answer 12

This is unlikely to directly affect the space occupying constituents of the cranium, and thus is unlikely to raise ICP, but a large contrast volume may transiently raise ICP

Question 13

Is any particular anesthetic better than another for reducing seizures following myelograms?

Answer 13

No. Neither anesthetic regimen nor duration of anesthesia affected the frequency of complications following myelography
There is no evidence acepromazine lowers the threshold for seizures, so it is possible for it to be used and may be the best option

Question 14

Is ICP likely to be a problem in an animal with hydrocephalus and an open fontanelle?

Answer 14

ICP changes associated with general anesthesia are blunted or minimized due to compliance of the open sutures or open fontanel

Question 15

How much of cardiac output do the brain and spinal cord receive?

Answer 15

15%

Question 16

What is increased ICP secondary to increased CBF prevented by?

Answer 16

Displacement of CSF from the cranium

Question 17

What is the Robin Hood effect?

Answer 17

Vasculature around disease tissue may vasoconstrict, while disease tissue doesn’t –> results in diversion of blood to diseased tissue

Question 18

What fluids should be used if there is suspected ICP?

Answer 18

Hypertonic saline (7.5%)

Question 19

How can NMDA antagonism (Ketamine) prevent ischemic injury?

Answer 19

A reduction of glutamate neurotoxicity

Question 20

What volatile anesthetic should be used? Why?

Answer 20

Sevoflurane because it may not increase CBF until 1.5 MAC whereas others can cause increased CBF can occur with a MAC >1.0

Question 21

What is used to check for oxygenation?

Answer 21

Arterial blood gas

Question 22

What should be done if signs of increased ICP occur?

Answer 22

Hyperventilate patient

Administer hyperosmolar agents

Question 23

What is irritating to the cerebral parenchyma with myelography?

Answer 23

Iodinated contrast agents