Cerebral Perfusion And ICP

Question 1

What is the normal cerebral blood flow and at what level would cause ischaemia?

Answer 1

Normal cerebral blood flow = 55-60ml/100g brain tissue per minute

Ischaemia = 20ml/100g brain tissue per minutes

Question 2

What is the most significant factor which determines cerebral blood flow?

Answer 2

Cerebral perfusion pressure

Question 3

What factors regulate cerebral blood flow?

Answer 3

Cerebral perfusion pressure
Concentration of arterial C02
Arterial P02

Question 4

What is cerebral autoregulation?

Answer 4

The ability to maintain constant blood flow to the brain over a wide range of CPP (50-150mmHg)

Question 5

Is CPP is low does the arterioles constrict or dilate?

Answer 5

Dilate

Question 6

What are the 3 sub types of cerebral oedema?

Answer 6

Vasogenic oedema (extracellular oedema)
Cytotoxic oedema (intracellular oedema)
Interstitial oedema

Question 7

What is the Munro Kelly doctrine ?

Answer 7

When a new intracranial mass is introduced, a compensatory change in volume must occur
This change causes a decrease in the volume of venous blood or CSF to keep the total intracranial volume constant

Question 8

Through which foramina is the CSF displaced from the ventricular system?

Answer 8

Foramina of Luschka

Formaina of magendie

Question 9

Through which veins can the venous blood exit the venous system in the cranium if there is raised ICP?

Answer 9

Emissary veins or jugular veins

Question 10

What is the presentation of the cushings reflex?

Answer 10

Hypertension
Irregular breathing
Bradycardia

Question 11

In the cushings response what is responsible for bradycardia?

Answer 11

Mechanical distortion of the medulla
Sympathetic response causing tachycardia - this causes a negative feedback response from aortic baroreceptors causing bradycardia

Question 12

What ANS response is triggered with the cushings reflex and how?

Answer 12

An increase in ICP resulting in compression of cerebral arterioles triggers activation of the sympathetic NS

Question 13

How would you manage a patient with raised ICP?

Answer 13

Sit them up / elevate head
Mannitol / hypertonic saline 
Hyperventilation to decrease CBF
Barbiturate coma 
Surgical decompression 

Brain tissue oxygenation monitoring
Micro-dialysis

Question 14

What is responsible for the cushings reflex?

Answer 14

Raised ICP

Question 15

How do you treat the cushings response?

Answer 15

Elevate head to increase venous return
Barbiturate coma - to decrease brain metabolism therefore blood flow
Mannitol
Hypertonic saline
Hyperventilate 
Surgical decompression