Session 10 - Lecture 2: Raised ICP

Question 1

What is intracranial pressure?

Answer 1

Pressure inside the skull and thus brain tissue and CSF.

Question 2

What is classed as normal and raised intracranial pressure?

Answer 2

Normal:
Adults = 5-15mmHg
Children = 5-7mmHg
Term infant = 1.5-6mmHg
Raised = >20mmHg

Question 3

Describe the principles behind Monro-Kellie doctrine and give an example.

Answer 3

Any increase in volume of one cranial constituents must be compensated by a decrease in a volume of another e.g. venous volume, arterial, brain and CSF.
Example:
Breathing increases intrathoracic pressure, this increases venous pressure in brain and therefore CSF volume will decrease.

Question 4

Give some examples of causes of raised ICP.

Answer 4

Malignant hypertension, SVC obstruction, haemorrhage, hydrocephalus. To put simply, too much brain, blood, CSF or SOL.

Question 5

Describe the pathophysiology of congenital hydrocephalus.

Answer 5

Can be caused by neural tube defects, aqueductal stenosis, too much CSF production or not enough CSF absorption.

Question 6

What are the treatment options for congenital hydrocephalus?

Answer 6

External ventricular drain –> short term drain
Ventricular shunts –> longer term drain:
- Omayya reservoir (small tube connecting ventricle to omayya reservoir from which a syringe drains the excess fluid).
- Ventriculo-peritoneal shunt (tube goes to peritoneum, good when child is still growing as have extra loop).
- Ventriculo-atrial shunt (tube goes to right atrium, not good if child is still growing).

Question 7

Describe the different types of cerebral oedema that can occur.

Answer 7

Vasogenic = breakdown of tight junctions at the BBB.
Cytotoxic = intracellular retention of sodium and water.
Osmotic = increased osmolarity in the brain compared to serum.
Interstitial = rupture of BBB, CSF spreads to the interstitium.

Question 8

Up to what volume can venous blood and CSF compensate for raised ICP?

Answer 8

75ml each.

Question 9

Describe the normal ranges and relationship between mean arterial pressure, intracranial pressure and cerebral perfusion pressure. Also state the consequence of low CPP.

Answer 9

CPP = MAP-ICP
CCP = >70mmHg
MAP = 65-110mmHg
ICP = 5-15mmHg
If CPP drops to 60mmHg or less, there is a significant risk of hypoperfusion.

Question 10

Describe Cushing’s triad?

Answer 10

Symptoms of raised ICP: -

• Raised blood pressure (MAP)
• Bradycardia
• Irregular breathing

Question 11

List potential herniations that can occur within the brain.

Answer 11

Tonsillar, sub-falcine (under flax cerebri), uncal (temporal lobe), central downward (frontal lobe) and external herniations (through an open skull fracture).

Question 12

What are the signs and symptoms a patient may present with when they have raised ICP?

Answer 12

Headache (constant and worse on bending/coughing), nausea and vomiting, difficult concentrating, drowsiness, confusion, double vision (worsening, visual field defects, papilloedema, focal neurological signs and seizures.

Question 13

Describe how idiopathic intracranial hypertension can be diagnosed and what could help manage this condition.

Answer 13

Diagnosis is with lumbar puncture, the opening pressure will be high (>25cmH2O or >18mmHg).
Symptoms will improve after weight loss and blood pressure control.

Question 14

What are the treatment options for raised ICP?

Answer 14

Mannitol = draws fluid out of brain to blood stream (also has a diuretic effect).
3% hypertonic saline = see manitol
External ventricular drain
If all else fails, can use decompressive craniectomy.