Clinical Aspects of Cerebral Perfusion and ICP Flashcards

1
Q

what percentage is cerebral blood flow of cardiac output?

A

15%

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2
Q

what is the most significant factor that determines cerebral blood flow at any given time?

A

cerebral perfusion pressure

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3
Q

what is cerebral perfusion pressure?

A

effective blood pressure gradient across the brain

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4
Q

increased ICP causes the cerebral perfusion pressure to ….

A

decrease

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5
Q

what are the factors that regulate cerebral blood flow under physiological conditions

A

CPP concentration of arterial CO2 arterial PO2

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6
Q

what is cerebral auto regulation?

A

the ability to maintain constant blood flow to the brain over a wide range of CPP

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7
Q

what happens to the arterioles when CPP is low?

A

arterioles dilate to allow adequate flow at decreased pressure

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8
Q

what happens to arterioles when CPP is high

A

the cerebral arterioles constrict

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9
Q

can cerebral blood flow always be auto regulated?

A

no, when CPP exceeds 150mm hg, hypertension, the system fails

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10
Q

what is a prominant cause of subacute to chronic intracranial hypertension?

A

Cerebral edema

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11
Q

learn

A
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12
Q

a barrier composed of astrocytic foot process wrapping around a capillary endothelium is composed of what?

A

tight junctions

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13
Q

can all substances that are carried in the blood reach the neural tissue?

A

no

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14
Q

what is the function sof endothelial tight junctions?

A

barrier to the passive movement of many substances in order to protect the sensitive neural tissue form toxic materials

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15
Q

look

A
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16
Q

what are the mechanisms by which materials may be transported naturally across the endothelial cells?

A
  • lipid-soluble substances can usually penetrate all capillary endothelial cell membranes in a passive manner
  • amino acids and sugars are transported across the capillary endothelium by specific carrier-mediated mechanisms
17
Q

what happens when a new intracranial mass is introduced

A

a compensatory change in volume must occur through a reciprocal decrease in venous blood or CSF to keep the total intracranial volume constant

18
Q

what are the homeostatic mechanisms 8-15mmHG

A
  • The venous system collapses easily and squeezes venous blood out through the jugular veins or through the emissary and scalp veins
  • CSF can be displaced from the ventricular system through the foramina of Luschka and Magendie into the spinal subarachnoid space
  • When these compensatory mechanisms have been exhausted, small changes in volume produce significant increase in pressure
  • The innate homeostatic pressure-buffering mechanism offered by displacement of CSF and venous blood keeps compliance flat until a “critical volume” is reached
  • After this critical volume, small volumetric changes result in precipitous increases in pressure, and intracranial hypertension naturally ensues
19
Q

Characteristics of A waves?

A
  • Abrupt elevation in ICP for 5 to 20 minutes followed by a rapid fall in the pressure to resting levels
  • The amplitude may reach as high as 50 to 100 mm Hg
20
Q

characteristics of B waves

A

•Frequency of 0.5 to 2 waves per minute, are related to rhythmic variations in breathing

21
Q

characteristics of C waves

A

•Rhythmic variations related to waves of systemic blood pressure and have smaller amplitude

22
Q

what is cushings reflex?

A
  • Vasopressor response
  • Hypertension, irregular breathing and bradycardia
  • Increased ICP more than MAP
  • Compression of cerebral arterioles
  • Decreased CBF, activation autonomic nervous system
  • Sympathetic response: alpha-1 adrenergic receptors -> Hypertension and tachycardia
  • Aortic baro-receptors stimulate vagus nerve -> Bradycardia
  • Bradycardia also due to mechanical distortion of medulla
23
Q

whats the management of increased ICP?

A
  • Head end elevation: facilitate venous return
  • Mannitol/ Hypertonic saline
  • Hyperventilation: decrease CBF (temporary measure)
  • Barbiturate coma: decrease cerebral metabolism, CBF
  • Surgical decompression
24
Q
A