Cerebral Flow III

What is the blood supply of the brain?

Two internal carotid arteries and the two vertebral arteries join to form the circle of Willis, supplying blood to various regions of the brain.

Which three compartments does the skull hold?

1. Brain tissue

2. Blood

3. CSF

Monro - Kellie doctrine

If there is any change in one of the three compartments of the skull (brain, blood, or CSF), there must be a compensatory change in the others to maintain intracranial pressure.

If there is a blockage in the flow of CSF, what happens to ICP?

It increased because CSF accumulates

When do we calculate CBF?

When ICP is rased

What’s a normal ICP?

4-15mmHg (50-200 mm water)

What can influence ICP?

Venous and Arterial pressure

Abdominal and intra-thoracic pressure

Posture

Temperature

Blood gases

What is CPP? What is its equation?

Cerebral Perfusion Pressure
The pressure needed to overcome ICP in order to deliver O2 and nutrients to the brain tissue.

CPP = MAP - ICP

What can increase Brain volume?

A lesion or an Oedema which increases brain water

Types of Oedemas

1. Vasogenic

2. Cytotoxic

3. Osmotic

4. Hydrostatic

Vasogenic Oedema

Is a type of brain swelling that occurs when the blood-brain barrier is disrupted, leading to the leakage of fluid into the extracellular space.

What is Cytotoxic Oedema?

Cytotoxic Oedema is a type of brain swelling that results from the failure of cellular ion pumps, causing intracellular fluid accumulation and cell swelling, typically following ischemia or metabolic disturbances. This condition disrupts cellular homeostasis and can lead to brain cell injury and dysfunction.

What is Osmotic oedema?

Osmotic oedema occurs when there is an imbalance in osmotic gradients, typically due to changes in plasma or tissue osmolarity, leading to the movement of water into the cells and causing cell swelling.

What is Hydrostatic Oedema?

Hydrostatic oedema is a type of fluid accumulation in the brain caused by increased hydrostatic pressure within the vascular system, often resulting from conditions such as congestive heart failure or venous obstruction. This pressure causes fluid to leak from blood vessels into surrounding brain tissue, leading to swelling and potential neurological impairment.

What is compliance?

How well the skull can accommodate changes in volume without causing a big increase in pressure

What decreases compliance?

hypercarbia

hypoxia

sleep

anaesthesia

What increases compliance?

hypocarbia

hyperoxia

hypothermia

barbiturates

How can we measure ICP?

1. Lumbar puncture (not accurate)

2. Ventricular cannulation (more accurate)

3. Subdural sensor

4. Extradural sensor

3 and 4 are the safest and most reliable

What effects can increased ICP have on vital signs?

Decreases resp rate

Brachy-cardia

Arrhythmias

Constricted pupils and unilateral pupillary dilation

Increased pulse pressure

Increased arterial bp

What happens to cerebral blood flow when ICP is raised?

It is reduced (CPP = MAP - ICP), leading to potential ischemia and further neurological damage.

How does increased ICP affect CSF?

Increases it by cerebral vasodilation

How does increased IPC and CSF affect cerebral blood volume?

They increase it (because of the cerebral vasodilation that increased CSF)

What are some clinical effects of increased ICP?

Headaches (max in the morning, relieved after vomiting), vomiting, papilledema(most reliable sign)

What are the main features of Papolloedema?

Swelling of the optic disc due to increased ICP

blurred vision

visual field defects

What are some neurological defects of raised ICP?

Headache when waking

irritability

vomiting

encephalopathy (confusion, drowsiness, come)

brain herniation (death)

Cingulate herniation

Compression of internal and anterior cerebral veins

Central transtentorial herniation

Compression of 3rd nerve, posterior cerebral artery, ischemia or compression of brainstem

Uncal herniation

compression of mid brain, 3rd nerve and posterior cerebral artery

Tonsilar herniation

Herniation of cerebellar tonsils which leads to compression of the medulla, coma, cv and resp problems and potentially death.

Treatment of ICP

1. Sedation and positioning

2. Hypertonic solutions

3. Hyperventilation

4. Steroids

5. Hyperbaric oxygen (barely used)

6. Hypothermia

7. Induced barbiturate coma