Central Nervous System

Question 1

How do you calculate CPP

Answer 1

CPP = MAP - [ICP + CVP]

CPP approx 80mmHg

Question 2

Effect on CBF:

O2

CO2

Volatiles

N2O

NMBA

Induction agents

Answer 2

Effect on CBF:

O2: hypoxic vasodilation below 8kPa

CO2: vasodilator linear 3-10kPa

Volatiles: all increase CBF reduce CMRO2

N2O: increase CBF and increase CMFO2

NMBA: no effect

Induction agents: all reduce except ketamine

Question 3

Monroe Kellie doctrine

Answer 3

Brain 80%
Blood 12%
CSF 8%

Normal ICP 10-15mmHg
>20 elevated ICP

Question 4

CSF:

What if it?

Where is it produced?

Volumes:

Answer 4

CSF:

What if it?
Clear colourless solution that bathed the brain and spinal cord as a fluid layer for protection of the CNS

Where is it produced?
Choroid plexuses located in third/fourth and lateral ventricles
Plasma filtration and subsequent secretion

Volumes:
Total volume 150ml
Produced at 0.3ml/min
Replaced 3xday

Question 5

Describe circulation of CSF

Answer 5

Lateral foramen through foramen of Monroe

3rd ventricle

Aqueduct of Sylvius into 4th ventricle

CSF leaves ventricular system via midline foramen of Magendie and lateral foramen of Lushka entering sub arachnoid space

CSF absorbed into dural venous sinuses via arachnoid villi and granulations that project into dural sinuses

Question 6

Compare CSF to plasma

Answer 6

CSF compared to plasma:

1% protein therefore reduced buffer

Ca 50% lower

Glucose 60% of plasma

Cl and Mg levels higher

Question 7

What is:

Cerebral blood flow?

White matter?

Grey matter?

Resting O2 requirements?

Answer 7

Cerebral blood flow?
50ml/100g brain tissue

White matter?
20ml/100g/min

Grey matter?
70ml/100g/min

Resting O2 requirements?
50ml/min (20% total body oxygen requirements)

Question 8

Describe bloody supply to the brain

Answer 8

Carotid and vertebral arteries

2/3rds supplied by internal carotids