increased intracranial pressure

Question 1

3 components of the cranium?

Answer 1

1. brain tissue (80%)- non modifiable
2. blood (10%)- blood supply to brain can increase or decrease
3. CSF (10%)- modifiable: CSF can be displaced, reabsorbed or secretion can decrease

Question 2

usual ICP?

Answer 2

5-15 mmHg- an increase or decrease in any of the 3 will alter ICP

Question 3

can you measure ICP?

Answer 3

not really- you work with it indirectly

Question 4

what is the monro-kellie hypothesis?

Answer 4

it is a hypothesis to explain minor pressure changes

• to maintain homeostasis within the cranium, an increase in volume of any 1 component, results in a decrease in volume of another component to keep ICP stable
• ONLY works for minor changes in ICP (ex. bending over blood rushes to head—> increased BV of cranium, CSF will be displaced, reabsorbed or secretion will decrease)

Question 5

problems occur when you run into…

Answer 5

MAJOR changes!

• the skull is not expandable
• major changes from proliferating/growing lesions, such as a tumor or hemorrhage, will cause an increase in ICP
• adaptation only works to a certain extent
• with space occupying lesions present, pressure increases within the cranium because the skull cannot expand to increase the available space

Question 6

1st compliance the body does to compensate for changes?

Answer 6

CSF displaced, reabsorbed or decreased secretion to relieve some of the pressure (from ventricles of brain to spinal cord)… not all of it obviously

Question 7

2nd compliance the body does to compensate for changes?

Answer 7

venous compression to decrease BF to the brain (only can go so far) it is limited because it could lead to cerebral ischemia, you have room until 50 mmHg. if BP is to point of decreased perfusion, then infarction and irreversible damage occurs

Question 8

final consequence of major changes…

Answer 8

neither of the compliances are adequate… increased ICP leads to compression and displacement of brain tissue (foramen magnum), ultimately death

Question 9

what is the cushings reflex?

Answer 9

NOTHING to do with cushings reflex- brains late response to ICP
reflex is triggered by cerebral ischemia (<50 mmHg)—-> specifically in the brainstem and vasomotor control center

Question 10

cerebral perfusion pressure?

Answer 10

CPP= pressure required to maintain adequate blood flow to brain
CPP= MAP- ICP
CPP is usually ~ 70-100 mmHg

Question 11

MAP=

Answer 11

systolic p + 2(diastolic p)/ 3

Question 12

if CPP is less than… ____ ischemia occurs

Answer 12

40 mmHg (50??)

Question 13

CUSHINGS TRIAD??

Answer 13

1) widening pulse pressure (systolic-diastolic) due to either a drop in diastolic or rise in systolic, and a rapid onset of HTN (just high bp- not disease!)
2) reflexive bradycardia (initially heart is tachycardia in response to venous compression and decreased BF, but increased HR increases ICP so HR slows!)
3) irregular breathing (brain regulates breathing, so when this function depressed—> normal baseline breathing patterns are altered!)