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Anesthesia > CNS & PNS > Flashcards

CNS & PNS Flashcards

1
Q

The Edinger-Westphal nucleus consists of smaller preganglionic parasympathetics that travel in which cranial nerve?

A

CN III - oculomotor nerve

Mediates pupillary light reflex and accommodation

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2
Q

What sensations are transmitted by the afferent spinothalamic tract?

A

temperature

pain

touch

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3
Q

Name the main arteries from which the Circle of Willis arises.

A

ICAs –> MCAs

Vertebral arteries –> Basilar artery

ACA, anterior communicating, PCA, posterior communicating (connects anterior and posterior circulation)

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4
Q

What arteries do the ICA and VAs branch off of?

A

Right - brachiocephalic –> common carotid –> ICA, ECA

Left - aorta arch –> common carotid –> ICA, ECA

Subclavian –> vertebral arteries

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5
Q

What are the common sites of Vertebral artery dissection?

A

transverse foramen of C6

exiting at C2

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6
Q

Which artery is formed by the convergence of medial branches of the VAs just prior to the basilar junction?

A

Anterior spinal arteries

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7
Q

What is the final drainage location of the transverse sinus?

A

sigmoid –> internal jugular veins

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8
Q

What are the contents of the cavernous sinus?

A

CN III, IV, V1, V2, VI

ICA

Sympathetic plexus

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9
Q

What is a typical measure of total cerebral blood flow (CBF)?

A

750 mL/min

~15-20% of cardiac output

50 mL/100 g/min

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10
Q

List the main determinants of cerebral blood flow.

A

autoregulation

cerebral perfusion pressure

respiratory gas tensions

cerebral metabolic rate of oxygen consumption (CMRO2) coupling

temperature

viscosity

some autonomic influences.

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11
Q

When does autoregulation occur and what does it ensure?

A

(MAPs) of 70 and 150 mmHg

decrease in CPP or MAP –> vasodilatation

increase in CPP or MAP –> vasoconstriction

patients with chronic HTN –> autoregulatory curve is shifted to the right for the lower and upper limits

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12
Q

When is cerebral blood flow dependent on MAP or cerebral perfusion pressure?

A

At the extremes of MAP (<70 mmHg or >150 mmHg), where cerebral autoregulation is non-existent, or in situations where cerebral autoregulation has been compromised (e.g. traumatic brain injury, stroke), CBF is dependent on MAP or CPP.

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13
Q

How does cerebral blood flow change in response to changes in PaCO2?

A

CBF changes proportionately to changes in PaCO2 (1-2 mL/100g brain tissue/min/mmHg change in PaCO2)

thought to be due to CO2 diffusing across the blood brain barrier –> changes in the pH

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14
Q

How does cerebral blood flow change in response to changes in PaO2?

A

Unlike the vigorous reactivity to changes in PaCO2, CBF is only altered when there are EXTREME changes in PaO2.

minor change in CBF with hyperoxemia.

marked inc in CBF with hypoxemia (PaO2 <50mmHg)

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15
Q

How does cerebral blood flow change in response to changes in CMRO2?

A

blood flow increases or is greatest where CMRO2 is greatest

This safety mechanism provides protection against hypoxia or anoxia

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16
Q

By how much does cerebral blood flow change in response to a degree change in temperature?

A

CBF changes by 5-7% per degree Celsius change in temperature.

Both CMRO2 and CBF increase as temperature increases and vice versa

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17
Q

How do changes in viscosity affect cerebral blood flow?

A

Decreased viscosity (low Hct) –> increased CBF to preserve cerebral oxygen supply

In contrast, CBF decreases at extremes of increased viscosity, such as polycythemia

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18
Q

What happens to cerebral blood flow during periods of intense sympathetic drive?

A

parasympathetic (vasodilatory)

sympathetic (vasoconstricting)

noradrenergic fibers

intense or prolonged sympathetic drive –> vasoconstrict and restrict CBF

Under most circumstances, however, the other “drivers”(e.g., pCO2, CMRO2, PO2 at extremes) of CBF supersede sympathetic or parasympathetic effects.

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19
Q

What levels of cerebral blood flow are associated with an isoelectric EEG and irreversible brain damage (in ml/g/min)?

A

10-15 mL/100 g/min –> isoelectric EEG

<10 mL/100 g/min –> irreversible brain damage

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20
Q

What is the formula for cerebral perfusion pressure (CPP)?

A

CPP = MAP - ICP or CVP whichever is greater

Because ICP, CVP are usually <10mmHg, CPP is primarily determined by MAP

Normal CPP is ~80-100mmHg

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21
Q

What determines the ability of a substance to traverse the blood-brain barrier?

A

Size, charge, hydrophobicity and degree of protein binding determine ability to cross the BBB

Smaller, freestanding, more lipid-soluble molecules can cross the BBB >>> than larger, less lipid-soluble molecules with a higher degree of protein binding

22
Q

What is the circulatory steal phenomenon or inverse steal?

A

In the normal brain, volatile anesthetics –> vasodilatation of cerebral vessels.

Arterioles are maximally dilated in areas of ischemia, = volatile anesthetics cannot further vasodilate these regions.

If volatile anesthetics are given in the setting of focal ischemia, blood flow may potentially be redistributed away from ischemic tissue to normal tissue and lead to further damage

Hypercarbia does the same thing

23
Q

Name some factors that may alter cerebral autoregulation.

A
  1. chronic hypertension - shifted to the right
  2. hypercapnia –> vasodilaion
  3. hypocapnia –> vasoconstriction
  4. Anemia and hemodilution –> decrease the vascular tone –> increase CBF
  5. mild hypothermia impairs cerebral autoregulation
  6. mild hyperthermia enhances cerebral autoregulation
  7. Volatile anesthetics
24
Q

How do volatile anesthetics influence cerebral blood flow auto-regulation?

A

significantly impair autoregulation

CBF is preserved to lower MAP

autoregulation in response to rising MAP is impaired

1 MAC or less, sevoflurane causes less impairment than other volatile anesthetics

25
Q

Name disease states that may abolish autoregulation.

A

acute ischemia

mass lesions

trauma

inflammation

diabetes mellitus

26
Q

The most medial portions of the motor homunculus are responsible for movement of what body parts?

A

Gentials

Toes

Feet

Legs

27
Q

What circuit links the hippocampus with the cingulate cortex?

A

The Papez circuit links the hippocampus with the cingulate cortex via the mammillary bodies and the anterior thalamus

28
Q

What structure assists with vestibular balance?

A

Cerebellum

29
Q

What part of the brainstem plays a large role in consciousness and awareness?

A

reticular activating system

30
Q

Which area of the frontal lobe is MOST responsible for coordinating patterns of movement?

A

Premotor cortex

31
Q

Match the following areas of the brain with its associated neurotransmitter:

raphe nuclei, cerebral cortex, substantia nigra

locus ceruleus

A

raphe nuclei - serotonin

cortex - glutamate or GABA

substantia nigra - dopamine

locus ceruleus - norepinephrine

32
Q

What is a penumbra?

A

area of ischemic brain in which cellular dysfunction is temporarily reversible

neuronal cell death can be avoided if cerebral blood flow is restored

33
Q

What are two potential ways that focal cerebral ischemia can occur?

A

surgical clip/clamp placed on a vessel

hypotension

34
Q

What is the value for normal cerebral blood flow?

A

50 mL/100g/minute

35
Q

How does hyperglycemia contribute to injury during ischemia?

A

During an ischemic event, glucose –> increased lactate production via anaerobic glycolysis

hyperglycemia –> poor neurologic outcome

36
Q

How do brain tumors affect cerebral blood flow?

A

Not much data

lower CBF than normal brain tissue

may increase ICP –> reduce CPP, CBF –> ischemia

37
Q

How much CSF is present in the cranium at any given point in time?

A

150 mL of CSF in the CNS (half in the cranium, and half in the spinal space)

Produces - 20 mL/hour, or approximately 500 mL/day –> replenished 3-4 times daily

60ml in neonates

38
Q

Where does most CSF flow begin?

A

Ependymal cells of the choroid plexus (lateral ventricles) +

Brain interstitium (via transependymal diffusion)

produce CSF

39
Q

Where does CSF absoprtion occur?

A

arachnoid villi and granulations in the superior sagittal sinus

40
Q

What are the areas of the brain that lack a traditional blood-brain barrier?

A

choroid plexi

hypothalamus

pituitary

area postrema (implicated as the chemoreceptor trigger zone for emesis)

41
Q

Compared to blood, describe relative concentrations of major electrolytes and macromolecules in CSF

A

isotonic

lower protein, glucose, calcium and potassium

higher sodium, chloride and magnesium

42
Q

What are the different types of cognitive changes that manifest after anesthesia?

A

delirium

post-operative cognitive dysfunction (POCD) or dementia

43
Q

What is the definition of delirium?

A

acute cognitive disorder, characterized by change in attention, cognition, consciousness, and perception

44
Q

What are the different types of delirium in the perioperative setting?

A
  1. Emergence Delirium (ED) - during or immediately after emergence from general anesthesia (GA) and resolves within minutes or hours
  2. Post-operative Delirium (PD) - peaks between POD 1 and 3 and usually resolves within hours to days
45
Q

What are the risk factors for emergence delirium?

A

predominance in children, and a peak incidence between ages 2 and 4

rapid emergence (most often with sevoflurane and desflurane)

Risk factors include pre-operative medication with midazolam, breast surgery, abdominal surgery, and prolonged duration of surgery

46
Q

What are the risk factors for post-operative delirium?

A

older patients

higher incidence after hip fracture surgery

greater intraoperative blood loss

pain

more post-operative blood transfusions

post-operative hematocrit < 30%

47
Q

What drugs have been used to treat or prevent emergence and post-op delerium?

A

midazolam

clonidine

dexmedetomidine

fentanyl

ketorolac

48
Q

What is post-operative cognitive dysfunction (POCD)?

A

mild cognitive disorder after surgery or anesthesia

impairment of memory

learning difficulties

reduced ability to concentrate

49
Q

What are the risk factors for POCD?

A

advanced age

type of surgery (major surgery such as cardiac or neurosurgery)

increased duration of anesthesia

pre-operative cognitive impairment

depression

fewer years of education

second operations during the same hospitalization

post-operative infections and respiratory complications

history of previous cerebrovascular accident (CVA) with no residual impairment

POCD at hospital discharge

50
Q

What are the risk factors for POCD in cardiac surgery?

A

E4 allele of the ApoE gene

poor left ventricular function

longer duration of CPB

presence of atrial fibrillation or peripheral vascular disease

prior stroke

diabetes.

Anesthesia (25 decks)

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