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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
process of autoregulation
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
what does increase in PCO2 cause
vasodilation which causes additional blood volume, which may not be able to be accommodated in the brain and so can cause raised ICP
27
what does decrease in PCO2 cause
vasoconstriction
28
what does decrease in PO2 cause
vasodilation which causes additional blood volume which may not be able to be accommodated in the brain and so can cause raised ICP
29
what happens when brain activity increases
greater production of metabolites, especially CO2 leading to vasodilation. Reducing cerebral metabolism helps keep ICP down. The worst situation is a fitting brain
30
what mechanism deals with raised ICP and reduced cerebral perfusion pressure?
Cushing's response
31
what is cushing's response?
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
what are the 2 phases of damage?
primary and seconday injury
33
what are the primary injuries causing raised ICP
focal lesion - tumour and bleed | diffuse damage - injury and infection
34
what does a midline shift on a CT scan show?
raised ICP, harmatoma/ bleed etc.
35
secondary brain injury
skull protects from primary injury but may worsen secondary injury swelling>increases ICP> decreased CPP>decreased perfusion>ischaemia> secondary injury
36
what can primary and secondary injury do?
damaged the BBB leading to greater fluid loss from the intravascular space and worse swelling
37
how to prevent secondary injury
maintains normal/ high arterial Blood pressure | prevent rises in ICP
38
how to improve outcomes in head injury?
prevent hypotension | avoid hypoxia
39
what clinical features guide management of raised ICP
observations - BP/HR/oxygen sats/ CO2/ temperature focal signs - pupils, sensory and motor function global function - level of consciousness - GCS and AVPU
40
GCS
Glasgow Coma Scale | ranges from 3-15
41
what GCS is it time for intervention?
GCS of 8
42
what happens if the brain continues to swell | ?
no more CSF transfer can occur | ICP increases greatly leading to vascular compression and impaired perfusion
43
what happens on a brain scan when there is an increase ICP
ventricles are compressed and so they do not appear much on the scan, no black shapes in the centre
44
what is coning?
continuing rise in ICP forces the cerebellar tonsils down into the foramen magnum
45
what happens when a patient is said to have coned?
brainstem and cranial nerves compressed | when ICP is greater than systolic BP, blood flow ceases
46
what happens when ICP exceeds blood pressure
cessation of perfusion and brain stem death
47
what happens to BP when there is raised ICP?
increase to attempt to maintain perfusion
48
brainstem death testing
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
what are the brainstem reflexes tested when testing for brainstem death?
``` cornea pupillary pharyngeal tracheal vestibular ```
50
what is heart rate without vagal innervation?
110bpm
51
what is blood pressure without sympathetic tone?
90/40mmHg
52
what other changes can be seen with brainstem death?
hypothalamic failure | pituitary failure
53
what does hypothalamic failure cause?
hypothermia as temperature regulation ceases
54
what does pituitary failure cause?
no ADH secretion - diabetes insipidus (polyuria)

Physiology 2 (20 decks)

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