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Nervous system > Inter cranial pressure and cerebral blood flow > Flashcards

Inter cranial pressure and cerebral blood flow Flashcards

1
Q

What is ICP?

A

Pressure of tissues inside cranial cavity

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2
Q

What is CBF?

A

Cerebral blood flow

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3
Q

Normal ICP

A

5-10 mmHg

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4
Q

Symptoms of small changes in ICP

A

Headaches and nausea

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5
Q

Symptoms of large changes of ICP

A

Impaired perfusion/ischaemia

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6
Q

What is ischaemia?

A

Restriction of blood supply to tissues causing shortage of oxygen

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7
Q

How to calculate perfusion pressure

A

MAP - CVP

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8
Q

What is MAP?

A

Mean arterial pressure

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9
Q

What is CVP?

A

Central venous pressure

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10
Q

How to calculate cerebral perfusion pressure

A

MAP - ICP

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11
Q

What is the Monroe-Kellie hypothesis?

A

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

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12
Q

What is cerebral atrophy?

A

Loss of neurons, fluid takes its place

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13
Q

What is the blood-brain barrier?

A

Restricts fluid movement between intravascular and interstitial spaces

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14
Q

Function of CSF

A

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

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15
Q

Why can you get a headache after a lumbar puncture?

A

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

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16
Q

Composition of CSF

A

No cells, virtually no protein

Markers, especially beta2 transferrin

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17
Q

How does blood regulate ICP?

A

Veins change diameter

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18
Q

How does CSF regulate ICP?

A

Easily moved between cranial and spinal spaces

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19
Q

How much ICP is produced a day?

A

Constant rate of 500mL/day

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20
Q

Where is CSF mainly produced?

A

Choroid plexus in lateral and 3rd ventricles

21
Q

Circulation of CSF

A

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

22
Q

What is hydrocephalus?

A

CSF blockage increases ICP

23
Q

What is the communicating pathway of CSF?

A

Blocked CSF reabsorption at arachnoid granulations but CSF circulation normal

24
Q

What is the non-communicating pathway of CSF?

A

Blocked CSF circulation - tumour, haemorrhage etc

25
Q

What is a communicating pathway?

A

CSF can flow between ventricles

26
Q

What is a non-communicating pathway?

A

Flow of CSF blocked between ventricles

27
Q

How is hydrocephalus treated?

A

Ventriculoperitoneal shunt to drain fluid

28
Q

How much blood normally flows to the brain?

A

50-60 mL/100g/minute

29
Q

What is cerebral perfusion?

A

Passage of blood or other fluid through vascular bed

30
Q

What is hypovolaemia?

A

Volume depletion

31
Q

How to calculate blood flow

A

Perfusion pressure / vascular resistance

32
Q

Process of auto regulation

A

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

33
Q

Effect of increased pO2 on CBF

A

Vasodilation

34
Q

Effect of decreased pCO2 on CBF

A

Vasoconstriction

35
Q

Effect of decreased pO2 on CBF

A

Vasodilation

36
Q

What is Cushing’s response?

A

Rise in ICP results in fall in CPP

Commonly associated with reflex bradycardia

37
Q

How to calculate CPP

A

MAP - ICP

38
Q

How does ICP impact CPP?

A

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

39
Q

2 examples of focal lesion

A

Tumour, bleed etc

40
Q

2 examples of diffuse damage

A

Injury

Infection

41
Q

Cycle of healing from a primary injury

A 
Injury
Swelling
Increased ICP
Decreased CPP
Decreased perfusion
Ischaemia
Secondary injury
42
Q

How to improve outcome in head injury

A

Prevent hypotension

Avod hypoxia

43
Q

What is a bad GCS score?

A

Above 8

44
Q

What happens when brain continues to swell?

A

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

45
Q

What is coning?

A

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

46
Q

What is hypothalamic failure?

A

Hypothermia as temperature regulation ceases

47
Q

What is pituitary failure?

A

No ADH released - diabetes inspidus and lots of urine

48
Q

How do you decide if someone as experienced brainstem death?

A
  • 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

Nervous system (24 decks)

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