Neuro

Question 1

Cerebral metabolism

Answer 1

Brain consumes 20% of total body oxygen –> most used to generate ATP for neuronal activity

Question 2

CMRO2

Answer 2

50 mL/min

- greatest in the grey matter of cortex

Question 3

Main energy for brain?

Answer 3

glucose ~ 5 mg/100g/min
- glucose transport into the brain independent of insulin

ketones during starvation

Question 4

Cerebral blood flow

Answer 4

varies w/ metabolic activity = parallels CMRO2
50 mL/100g

CBF governed by CMRO2, CPP, PaCO2, PaO2

Question 5

CBF regulation

Answer 5

1. Cerebral Perfusion Pressure = MAP-ICP
2. Autoregulation
3. Extrinsic Mechanisms

Question 6

Cerebral Perfusion Pressure

Answer 6

~80-100 mmHg

MAP - ICP

Question 7

Intracranial Pressure

Answer 7

~10 mmHg

Question 8

Autoregulation of CBF

Answer 8

cerebral vasculature dilates/constricts as necessary

• autoregulation between 60-160 mmHg
• drop in CPP = vasodilation to increase blood flow
• rise in CPP = vasoconstriction to decrease blood flow

Question 9

Relationship between pressure and volume of CBF

Answer 9

1 mmHg = 1 mL of blood

Question 10

Extrinsic mechanisms of blood flow

Answer 10

CBF is directly proportional to PaCO2
- this is secondary to changes in CSF [H+]

*only marked changes in PaO2 result in blood flow changes

Question 11

Temperature effect on CBF

Answer 11

hypothermia = reduced CMR + CBF (protective)
hyperthermia = increased CMR + CBF

Question 12

Responsiveness of brain areas to CO2

Answer 12

Cerebrum > cerebellum > spinal cord

Question 13

Blood brain barrier

Answer 13

vascular junctional endothelial cells in cerebrum are nearly fused together
- lipid bilayer allows lipid soluble substances through

Question 14

Plasma hypertonicity effect on BBB

Answer 14

water moves out of brain (shrink)

Question 15

Plasma hypotonicity effect on BBB

Answer 15

water moves into brain (swell)

Question 16

Sustained increases in ICP

Answer 16

lead to herniation –> skull and contents are a rigid structure
- compensation of reducing CBF by vasoconstriction is quickly maxed out

Question 17

Transmural pressure on an aneurysm?

Answer 17

with a large acute drop in ICP (CSF leak/drain) the MAP can lead to an aneurysm rupture

Question 18

Hyperventilation effect on ICP?

Answer 18

Dropping the PaCO2 will lead to a reduction in CBF and reduced ICP –> this will last approximately 6 hrs

Question 19

Volatile effects on CNS

Answer 19

1. All volatiles reduce CMR and CMRO2 (protective)

2. All cause dilation of cerebral vasculature –> increase CBF

Question 20

IV Anesthetic effects on CNS

Answer 20

1. Reduce CMR and CMRO2 (protective)

2. Cerebral vasoconstriction –> reduce CBF and therefore reduce ICP

Question 21

Ketamine effects on CNS

Answer 21

1. No change in CMR and CMRO2
2. Dilates cerebral vasculature and increases CBF and ICP

*However, NMDA antagonism may be protective against neuronal injury (blocks glutamate)

Question 22

Opioids effect on CNS

Answer 22

not much except respiratory depression can lead to increase PaCO2 and thus increase CBF and ICP

Question 23

Vasopressors

Answer 23

with normal autoregulation –> no effect really

Question 24

Vasodilators

Answer 24

cerebral vasodilation –> increased CBF and ICP

Question 25

Cerebral Ischemia Pathophysiology

Answer 25

brain utilized O2 reserves very quickly –> ischemia starts quickly
- ion derangements release glutamate which activates NMDA –> Ca2+ entry into cells –> damage to neurons