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M&M > Neurophysiology and Anesthesia > Flashcards

Neurophysiology and Anesthesia Flashcards

1
Q

What percentage of total body oxygen does brain consume?

A

20%

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2
Q

What is the cerebral metabolic rate (CMR) (in terms of oxygen consumption)

A

3-3.8mL/100g/min (50mL/min)

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3
Q

What parts of the brain are most sensitive to hypoxic injury

A

Hippocampus and cerebellum

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4
Q

What effect does hyperglycemia have on hypoxic brain injury

A

exacerbates injury by accelerating cerebral acidosis and cellular injury

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5
Q

What is average cerebral blood flow?

A

50mL/100g/min (~750ml/min) - 15-20% of cardiac output

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6
Q

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

A

CPP = MAP-ICP

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7
Q

At what CPP do we see slowing of EEG? At what CPP will EEG be flat?

A

<50mmHg, 25-40mmHg

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8
Q

At what range of MAP’s does cerebral blood flow remain constant (due to auto regulation)?

A

60-160mmHg

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9
Q

In which direction is the cerebral auto regulation curve shifted in patients with chronic HTN

A

right

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10
Q

How does PaCO2 affect CBF?

A

As PaCO2 increases, so does CBF (between PaCO2 of 20-80mmHg)

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11
Q

How does PaO2 affect CBF?

A

Only marked changes alter CBF. Severe hypoxemia (PaO2 <50mmHg) increases CBF

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12
Q

How does temperature affect CBF and CMR?

A

CBF changes 5-7% per 1˚C chang in temperature. Between 17 and 37˚, every 10˚ change results in a 50% increase/decrease in CMR.

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13
Q

What is the blood brain barrier made of? What does it allow to cross and what cannot cross it?

A

BBB is a lipid barrier.
Lipid-soluble substances can cross.
Restricts movement of ionized substances or those with high molecular weights.
O2 and CO2 are lipid-soluble, as are most anesthetic agents, so cross BBB.
Mannitol is a large protein and therefore would not.

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14
Q

How does water move across the BBB? How does changes in osmotic gradient (i.e., with increased tonicity with certain electrolytes) affect water movement?

A

Freely, via bulk flow.
Acute hypertonicity of plasma results in movement of water out of BBB into plasma (as is the case when mannitol is administered)

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15
Q

What is normal CSF production (in mL/h)?

What is total CSF volume?

A

21 mL/h; 150mL

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16
Q

What is normal ICP?

A

10mmHg or less

17
Q

Overall, how do volatile anesthetics influence CMR and CBF? Which volatile causes the greatest change in CMR? Greatest change in CBF?

A

Decreases CMR, slight increase CBF.
Isoflurane has greatest decrease in CMR (halothane least)
Halothane has greatest increase in CBF (sevoflurane the least).

18
Q

How to volatile anesthetics affect auto regulation in the brain?

A

Impair autoregulation

19
Q

How does an increase in CBF with volatiles affect ischemic parts of the brain?

A

Theoretically, there could be benefits with extra blood flow to injured parts of the brain. However, there may be a circulatory steal phenomenon, where volatile agents increase BF in normal parts of the brain, but not in ischemic areas (already maximally dilated)

20
Q

What is the net effect of volatiles on ICP?

A

Increase

21
Q

How does nitrous oxide affect CBF, CMR, and ICP?

A

Given in combination with IV anesthetics, minimal effect.
If combined with volatiles, may further increase CBF
Given alone, mild cerebral vasodilation and could increase ICP

22
Q

How do barbiturates affect CMR and CBF?

A

Decrease CMR, reduction in CBF (increased cerebrovascular resistance) Also their anticonvulsant properties can be helpful.

23
Q

How do opioids affect CBF, CMR, and ICP

A

No effect, unless PaCO2 rises secondary to respiratory depression

24
Q

How does etomidate affect CBF, CMR and ICP?

A

Decreases all three. May activate seizure foci in patients with epilepsy

25
Q

How does propofol affect CBF, CMR and ICP?

A

Decreases

26
Q

How do benzos affect CBF, CMR and ICP?

A

Decreases all three, but less so than propofol, barbiturates and etomidate

27
Q

How does ketamine affect CBF, CMR, and ICP?

A

Increases CBF (50-60%), no change in CMR, can increase ICP. No effect on ICP if given with propofol or a benzo

28
Q

How does lidocaine affect CMR, CBF and ICP?

A

Decreases all three, but less so than other agents

29
Q

How would the following anesthetic agents/conditions affect an EEG? (Activation or depression)

a) inhalational
b) barbituates
c) benzos
d) etomidate
e) ketamine
f) propofol
g) opioids
h) nitrous oxide
i) hypercapnia
j) hypocapnia
k) hypothermia
l) Hypoxia

A

a) activate (sub anesthetic), depress (1-2 MAC)
b) depress (activate in small doses)
c) activate (small doses), depress large doses
d) depress (activate in small doses)
e) activate
f) depress
g) depress
h) activate
i) mild - activate; marked - depress
j) depress
k) depress
l) early - activate; late - depress

M&M (4 decks)

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