Brain Injury

Question 1

What three components in the cranium provide intracranial pressure? What percentage do they contribute to the pressure?

Answer 1

1) brain tissue (80%)
2) blood (10%)
3) CSF (10%)

Question 2

What is CPP?

Answer 2

cerebral perfusion pressure, a measure of blood flow to the brain, it is NOT blood pressure

Question 3

How is CPP calculated?

Answer 3

CPP = MAP - ICP

Question 4

How is MAP calculated?

Answer 4

MAP = (SBP + 2DBP) / 3

Question 5

What is normal range for CPP?

Answer 5

70-100 mm Hg

Question 6

What CPP value would be dangerous and why?

Answer 6

A CPP of below 40-45 mm Hg is dangerous because there is a risk of ischemia from not perfusing the brain adequately.

Question 7

What is ICP and what is a normal ICP value?

Answer 7

Intracranial pressure is normally 5-15 mm Hg

Question 8

What is the Monro-Kellie hypothesis?

Answer 8

It states that because the components in the cranium (brain, blood, CSF) create a state of volume equilibrium. If there is an increase in the volume of one, it must be compensated by a decrease in another.

Question 9

What is the pathology of a brain injury?

Answer 9

• trauma leads to an abnormal change in one or more component in the cranium
• this leads to an increased ICP
• often the increased ICP is associated with a proliferating lesion (hemorrhage, tumour)
• because the skull cannot expand the body first displaces and/or reabsorbs CSF, this is the first compliance
• the second compliance is to reduce blood flow to the brain (limited because can’t go under 40 without risking ischemic infarction)
• final consequence is compression and displacement of the brain, which leads to death

Question 10

What is Cushing’s Reflex? What triggers it?

Answer 10

It is a later response of the brain to increased ICP, it is triggered by ischemia. It has three important presentations (triad):

1) widening pulse pressure/hypertension
2) reflexive bradycardia
3) irregular breathing

Question 11

What is a hematoma?

Answer 11

A collection of blood outside a blood vessel that is trapped in an organ or tissue.

Question 12

What is hemorrhage?

Answer 12

The escape of blood from a blood vessel, usually profuse or excessive.

Question 13

Who is more likely to get a hematoma and why?

Answer 13

Individuals older than 50 are more likely to get a hematoma because of vascular degeneration.

Question 14

What are two problems that hemorrhage and hematoma can cause?

Answer 14

1) hypovolemia from blood loss

2) increased ICP

Question 15

What is the pathophysiology of hemorrhage and hematoma?

Answer 15

• vascular trauma
• leads to hemorrhage
• leads to hematoma
• causes a loss of neural function in the affected area due to ischemia
• also causes a loss of function in the area controlled by the affected part of the brain

Question 16

What are three types of hematomas?

Answer 16

1) intracerebral hematoma = hemorrhage into brain tissue
2) subdural hematoma = between dura mater and arachnoid mater
3) epidural hematoma = between the skull and dura mater

Question 17

What normally causes an epidural hematoma?

Answer 17

head injury or fracture

Question 18

Which artery is usually affected when there is an epidural hematoma?

Answer 18

middle meningeal artery

Question 19

What is an added worry with a subdural hematoma?

Answer 19

In a subdural hematoma, there can be fibroblastic activity that causes the mass to become encapsulated. The sanguineous fluid in the mass has a high osmotic pressure and draws fluid in from the surrounding subarachnoid space. This increases the size of the mass and can also dehydrate the brain.