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Physiology 2 > Intracranial pressure > Flashcards

Intracranial pressure Flashcards

1
Q

What does changes in ICP cause?

A

Headache
nausea
impaired perfusion
ischaemia

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2
Q

perfusion pressure

A

Mean arterial pressure - central venous pressure

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3
Q

cerebral perfusion pressure

A

mean arterial pressure - ICP

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4
Q

what will happen to cerebral perfusion pressure if ICP increases?

A

will reduce it

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5
Q

what is the monro-kellie hypothesis?

A

volume of cranium is fixed
any increase in volume of one of the contents of the cranium must be compensated by a decrease in volume of another
A decrease in one component will lead to an increase in another, e.g. cerebral atrophy

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6
Q

what is the contents of the cranium?

A

brain
CSF
blood
they are all incompressible

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7
Q

what does cerebral atrophy look like on a scan?

A

more black areas in sulci

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8
Q

composition of CSF

A 
similar to interstitial fluid
no protein
water
sugar
fatty acids
amino acids
salts 
WBCs 
cell-waste products
neurotransmitters 
hormones
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9
Q

what marker is found in CSF?

A

Beta 2 transferrin

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10
Q

what is a raised ICP

A

cerebral vasodilation

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11
Q

what is the rate of CSF production?

A

500ml/ day

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12
Q

how often is CSF replenished?

A

3-4 times per day

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13
Q

CSF production

A

energy dependent - sodium/ potassium pump and ATPase

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14
Q

what connects the lateral and 3rd ventricles?

A

foramina of Monro

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15
Q

what connects the 3rd ventricle and 4th ventricle?

A

aqueduct of sylvius

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16
Q

where are the arachnoid granulations found?

A

superior sagittal sinus

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17
Q

when does hypoxic damage start in the brain?

A

3 minutes

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18
Q

maintaining cerebral blood flow

A

body tries to maintain cerebral perfusion at the expense of parts of the circulation during hypovolaemia or shock

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19
Q

neurological control of blood flow

A

autonomic nervous system

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20
Q

humoral control of blood flow

A

renin/ angiotensin

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21
Q

local control of blood flow

A

autoregulation, how the brain blood flow is controlled

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22
Q

cerebral perfusion maintenance

A

there is no sympathetic innervation

the brain is unresponsive to circulating vasoconstrictors

23
Q

autoregulation of cerebral perfusion

A

local vascular control mechanism maintains constant blood flow despite varying blood pressure
achieved by vasomotor tone
myogenic and metabolic

24
Q

how to calculate blood flow

A

Q(blood flow) = perfusion pressure (P)/ vascular resistance (R)

25
Q

process of autoregulation

A

fall in blood pressure > inadequate tissue perfusion > pp oxygen decreases and pp CO2 increases > vasodilation and increase in local blood flow > cerebral blood flow restored
It isn’t a local effect and can be dangerous

26
Q

what does increase in PCO2 cause

A

vasodilation which causes additional blood volume, which may not be able to be accommodated in the brain and so can cause raised ICP

27
Q

what does decrease in PCO2 cause

A

vasoconstriction

28
Q

what does decrease in PO2 cause

A

vasodilation which causes additional blood volume which may not be able to be accommodated in the brain and so can cause raised ICP

29
Q

what happens when brain activity increases

A

greater production of metabolites, especially CO2 leading to vasodilation.
Reducing cerebral metabolism helps keep ICP down.
The worst situation is a fitting brain

30
Q

what mechanism deals with raised ICP and reduced cerebral perfusion pressure?

A

Cushing’s response

31
Q

what is cushing’s response?

A

higher ICP sensed in 4th ventricle generates an increase in mean arterial pressure to restore cerebral perfusion pressure, commonly associated with a reflex bradycardia
blood pressure increases in attempt to maintain perfusion despite rising ICP

32
Q

what are the 2 phases of damage?

A

primary and seconday injury

33
Q

what are the primary injuries causing raised ICP

A

focal lesion - tumour and bleed

diffuse damage - injury and infection

34
Q

what does a midline shift on a CT scan show?

A

raised ICP, harmatoma/ bleed etc.

35
Q

secondary brain injury

A

skull protects from primary injury but may worsen secondary injury
swelling>increases ICP> decreased CPP>decreased perfusion>ischaemia> secondary injury

36
Q

what can primary and secondary injury do?

A

damaged the BBB leading to greater fluid loss from the intravascular space and worse swelling

37
Q

how to prevent secondary injury

A

maintains normal/ high arterial Blood pressure

prevent rises in ICP

38
Q

how to improve outcomes in head injury?

A

prevent hypotension

avoid hypoxia

39
Q

what clinical features guide management of raised ICP

A

observations - BP/HR/oxygen sats/ CO2/ temperature
focal signs - pupils, sensory and motor function
global function - level of consciousness - GCS and AVPU

40
Q

GCS

A

Glasgow Coma Scale

ranges from 3-15

41
Q

what GCS is it time for intervention?

A

GCS of 8

42
Q

what happens if the brain continues to swell

?

A

no more CSF transfer can occur

ICP increases greatly leading to vascular compression and impaired perfusion

43
Q

what happens on a brain scan when there is an increase ICP

A

ventricles are compressed and so they do not appear much on the scan, no black shapes in the centre

44
Q

what is coning?

A

continuing rise in ICP forces the cerebellar tonsils down into the foramen magnum

45
Q

what happens when a patient is said to have coned?

A

brainstem and cranial nerves compressed

when ICP is greater than systolic BP, blood flow ceases

46
Q

what happens when ICP exceeds blood pressure

A

cessation of perfusion and brain stem death

47
Q

what happens to BP when there is raised ICP?

A

increase to attempt to maintain perfusion

48
Q

brainstem death testing

A

2 experienced doctors
tests function not activity or perfusion
cause must be known - drugs/metabolic/ hypothermia excluded, they must be heated to normal body temp first
no respiratory effort
series of brainstem reflexes
declared dead despite heart still beating

49
Q

what are the brainstem reflexes tested when testing for brainstem death?

A 
cornea
pupillary
pharyngeal 
tracheal
vestibular
50
Q

what is heart rate without vagal innervation?

A

110bpm

51
Q

what is blood pressure without sympathetic tone?

A

90/40mmHg

52
Q

what other changes can be seen with brainstem death?

A

hypothalamic failure

pituitary failure

53
Q

what does hypothalamic failure cause?

A

hypothermia as temperature regulation ceases

54
Q

what does pituitary failure cause?

A

no ADH secretion - diabetes insipidus (polyuria)

Physiology 2 (20 decks)

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