Inter cranial pressure and cerebral blood flow

Question 1

What is ICP?

Answer 1

Pressure of tissues inside cranial cavity

Question 2

What is CBF?

Answer 2

Cerebral blood flow

Question 3

Normal ICP

Answer 3

5-10 mmHg

Question 4

Symptoms of small changes in ICP

Answer 4

Headaches and nausea

Question 5

Symptoms of large changes of ICP

Answer 5

Impaired perfusion/ischaemia

Question 6

What is ischaemia?

Answer 6

Restriction of blood supply to tissues causing shortage of oxygen

Question 7

How to calculate perfusion pressure

Answer 7

MAP - CVP

Question 8

What is MAP?

Answer 8

Mean arterial pressure

Question 9

What is CVP?

Answer 9

Central venous pressure

Question 10

How to calculate cerebral perfusion pressure

Answer 10

MAP - ICP

Question 11

What is the Monroe-Kellie hypothesis?

Answer 11

Volume of cranium is fixed
Contents of cranium are incompressible
Any increase in volume of one of the components of the cranium must be compensated by a decrease in another

Question 12

What is cerebral atrophy?

Answer 12

Loss of neurons, fluid takes its place

Question 13

What is the blood-brain barrier?

Answer 13

Restricts fluid movement between intravascular and interstitial spaces

Question 14

Function of CSF

Answer 14

Cushions brain, regulates ICP, acts as transfer medium (delivers nutrients, eliminates metabolic products and circulates neurotransmitters)

Question 15

Why can you get a headache after a lumbar puncture?

Answer 15

CSF escapes from LP site, meaning brain sage and pulls on meningeal attachments (low pressure headache)
When ICP is raised can result in brain pulled into foramen magnum

Question 16

Composition of CSF

Answer 16

No cells, virtually no protein

Markers, especially beta2 transferrin

Question 17

How does blood regulate ICP?

Answer 17

Veins change diameter

Question 18

How does CSF regulate ICP?

Answer 18

Easily moved between cranial and spinal spaces

Question 19

How much ICP is produced a day?

Answer 19

Constant rate of 500mL/day

Question 20

Where is CSF mainly produced?

Answer 20

Choroid plexus in lateral and 3rd ventricles

Question 21

Circulation of CSF

Answer 21

Produced by choroid plexus in ventricles
Circulates into 3rd ventricle by foramina of Monroe
Flows into 4th ventricle via aqueduct
CSF circulates over surface of brain and spinal cord
Reabsorbed on brain surface via arachnoid granulations

Question 22

What is hydrocephalus?

Answer 22

CSF blockage increases ICP

Question 23

What is the communicating pathway of CSF?

Answer 23

Blocked CSF reabsorption at arachnoid granulations but CSF circulation normal

Question 24

What is the non-communicating pathway of CSF?

Answer 24

Blocked CSF circulation - tumour, haemorrhage etc

Question 25

What is a communicating pathway?

Answer 25

CSF can flow between ventricles

Question 26

What is a non-communicating pathway?

Answer 26

Flow of CSF blocked between ventricles

Question 27

How is hydrocephalus treated?

Answer 27

Ventriculoperitoneal shunt to drain fluid

Question 28

How much blood normally flows to the brain?

Answer 28

50-60 mL/100g/minute

Question 29

What is cerebral perfusion?

Answer 29

Passage of blood or other fluid through vascular bed

Question 30

What is hypovolaemia?

Answer 30

Volume depletion

Question 31

How to calculate blood flow

Answer 31

Perfusion pressure / vascular resistance

Question 32

Process of auto regulation

Answer 32

Fall in blood pressure - cerebral blood flow restores - inadequate tissue perfusion - decreased oxygen, increased co2, increased vasodilation - restores cerebral blood flow

Question 33

Effect of increased pO2 on CBF

Answer 33

Vasodilation

Question 34

Effect of decreased pCO2 on CBF

Answer 34

Vasoconstriction

Question 35

Effect of decreased pO2 on CBF

Answer 35

Vasodilation

Question 36

What is Cushing's response?

Answer 36

Rise in ICP results in fall in CPP | Commonly associated with reflex bradycardia

Question 37

How to calculate CPP

Answer 37

MAP - ICP

Question 38

How does ICP impact CPP?

Answer 38

Higher ICP sensed in 4th ventricle which generates an increase in MAP to restore CPP

Question 39

2 examples of focal lesion

Answer 39

Tumour, bleed etc

Question 40

2 examples of diffuse damage

Answer 40

Injury | Infection

Question 41

Cycle of healing from a primary injury

Answer 41

``` Injury Swelling Increased ICP Decreased CPP Decreased perfusion Ischaemia Secondary injury ```

Question 42

How to improve outcome in head injury

Answer 42

Prevent hypotension | Avod hypoxia

Question 43

What is a bad GCS score?

Answer 43

Above 8

Question 44

What happens when brain continues to swell?

Answer 44

No more CSF transfer occurring ICP goes up markedly, leading to vascular compression and impaired perfusion Coning

Question 45

What is coning?

Answer 45

Rise in ICP forces cerebellar tonsils down into foramen magnum: brainstem and cranial nerves compressed, when ICP>systolic BP, blood flow ceases

Question 46

What is hypothalamic failure?

Answer 46

Hypothermia as temperature regulation ceases

Question 47

What is pituitary failure?

Answer 47

No ADH released - diabetes inspidus and lots of urine

Question 48

How do you decide if someone as experienced brainstem death?

Answer 48

- Tests of function, not activity/perfusion - Cause must be known - drugs/metabolic and hypothermia excluded - No respiratory effect - Series of brainstem reflexes: cornea, pupillary, pharyngeal, tracheal, vestibular - Can be declared dead despite a beating heart