Raised ICP/meningitis/encephalitis

Question 1

What are the3 components which make up the cranial cavity

Answer 1

• brain
• blood
• CSF

Question 2

What can cause raised ICP?

Answer 2

As the brain and ventricles are enclosed by a rigid skull, they have a limited ability to accommodate additional volume.

• haematoma
• tumour
• excessive CSF
• hydrocephalus
• meningitis
• traumatic head injuries
• idiopathic intracranial hypertension

Question 3

What is the normal ICP?

Answer 3

7-15mmHg in the supine position

Question 4

How do you calculate Cerebral perfusion pressure?

Answer 4

Cerebal perfusion pressure is the net pressure gradient causing cerebral blood flow to the brain

CPP= MAP- ICP

Question 5

What are the features of raised ICP?

Answer 5

Headache
Vomiting
Reduced conscious levels
Papilloedema 
Cushing’s triad- widening pulse pressure, bradycardia, irregular breathing

Question 6

What investigations can be used for raised ICP?

Answer 6

Neuroimaging- CT or MRI is the key to investigating the underlying cause

Can do invasive ICP monitoring
(This is when a catheter is placed into the lateral ventricles of the brain to monitor the pressure, can also be used to take CSF samples and to drain small amounts of CSF to reduce the pressure)
A cut off of >20mmHg is often used to determine if further treatment is needed to reduce the ICP

Question 7

What is the management of raised ICP?

Answer 7

Investigate and treat the underlying cause
Head elevation to 30 degrees
IV mannitol may be used as an osmotic diuretic
Controlled hyperventilation
Removal of CSF
- drain from intraventricular monitor, repeated lumbar puncture (this is done in idiopathic intracranial hypertension, ventriculoperitoneal shunt (for hydrocephalus

Question 8

What is cushing reflex?

Answer 8

Bradycardia, hypertension (systolic increases much more than diastolic, hence pulse pressure increases) and irregular breathing
Sign of raised ICP

Question 9

What is the pathophysiology behind cushing reflex?

Answer 9

When ICP becomes higher than MABP then the CPP decreases and you get cerebral ischaemia

Stage 1: Cerebral ischaemia leads to sympathetic nervous system being stimulated and vasoconstriction causing HTN, sympathetic nervous system also causes tachycardia

Stage 2: the hypertension stimulates baroreceptors in the aortic arch which stimulates parasympathetic system and leads to bradycardia

Stage 3: hypertension with increased ICP presses on the respiratory centre on the brain stem and causes irregular breathing