ICP & Hydrocephalus Flashcards
The brain makes up 80-85% of the head and blood and CSF make up the extra 20-25%. How much in mls is there approx of each?
Brain - 1300-1750ml
Blood - 100-150ml
CSF - 100-150ml
What is the normal ICP at rest and when may it be physiologically negative?
- 7-15mmHg
- when in vertical position
explain the Monro-Kellie-Doctrine
Compensatory mechanism for expanding masses - immediate compensation is decrease in CSF by moving it out of foramen magnum and decreased in blood volume by squeezing sinuses. Delayed compensation is decrease in extra cellular fluid
Approx. How much CSF is secreted a day?
500mls/day
What is the cerebral perfusion pressure equation?
Mean arterial pressure - intracranial pressure
What is the equation for cerebral blood flow?
Cerebral perfusion pressure divided by cerebral vascular resistance
What state would cause the cerebral perfusion pressure to be
MAP 100 - ICP 20 = CPP 80
Cushing’s response - MAP high because raised BP in Cushing’s, your ICP is high because reacting a lot
What state would cause the cerebral perfusion pressure to be
MAP 50 - ICP 20 = CPP 30?
Hypotension - MAP low because hypotensive and ICP high because pain maybe
What state would cause cerebral perfusion pressure to be
MAP 90 - ICP 10 = CPP 80?
Normal state
What is the normal at rest ICP and in what non-pathological state can it be negative?
- 7-15mmHg
- in vertical position
What is the easiest substance to release first according to Monro-Kellie doctrine? (CSF/venous blood)
- CSF first
- then venous blood
Through what foramina does CSF move from 4th ventricle into the subarachnoid space?
- two lateral foramina of Luschka
- medial foramen of Magendie
How does body auto regulate cerebral blood flow?
- pressure autoregulation - arterioles dilate/constrict in response to changes in BP or ICP
- metabolic autoregulation - arterioles dilate in response to chemicals e.g. lactic acid/CO2
Up to what mmHg can body autoregulate ICP?
50-150mmHg
What are the four mechanisms of raised ICP?
mass effect
brain swelling
increase in central venous pressure
problems with CSF flow
Give examples of mass effect causes of raised ICP.
tumour infarct contusions haematoma abscess
Give examples of causes of brain swelling that raises ICP. (5)
ischaemia/anoxia acute liver failure encephalopathy IIH hypercarbia
Give examples of causes of increase in central venous pressure.
venous sinus thrombosis
heart failure
obstruction of jugular veins
Give examples of causes of CSF flow problems causing raised ICP. (3)
obstruction (obstructive hydrocephalus) e.g. masses/chiari syndrome,
increased production e.g. choroid plexus papilloma,
decreased absorption so arachnoid granulations are blocked (communicating hydrocephalus) e.g. SAH, meningitis, malignant meningeal disease
What is treatment for choroid plexus papilloma and who tends to present with these tumours?
acetazolamide
children
What is normal newborn ICP?
1.5-6mmHg (often <0)
What is normal ICP in young children?
3-7mmHg
What is normal ICP in older children?
10-15mmHg
What are early signs & symptoms of raised ICP? (5)
- decreased consciousness level (bit drowsy)
- headache
- pupillary dysfunction +/- papilloedema
- changes in vision
- nausea and vomiting
What are later signs & symptoms of raised ICP? (6)
coma, fixed, dilated pupils, hemiplegia, bradycardia -> Cushing's triad, hyperthermia, increased urinary output
What are interventions for raised ICP? (7)
maintain head in midline, loosen tube ties/collars etc, Head of bead 30-45 degrees elevation to facilitate venous flow out , avoid gagging, coughing , decrease environmental stimuli treat hyperthermia maintain normal fluids, electrolytes
What is medical management for raised ICP? (4)
diuretics e.g. hypertonic saline (sometimes mannitol, furosemide, urea),
barbiturate coma (last resort),
antiepileptics (prophylactically),
surgical decompression
What is another description for hydrocephalus?
water on the brain
What is the difference between communicating/non-communicating hydrocephalus?
Communicating is where CSF can still flow at the ventricles
Non-communicating is where CSF is blocked at the ventricles
What is arrested hydrocephalus?
Hydrocephalus where patient has no symptoms because its compensated for
Which type of hydrocephalus (communicating/non-communicating) will appear with enlargement of lateral, 3rd and 4th ventricles?
Communicating
Which type of hydrocephalus (communicating/non-communicating) will appear with enlargement of frontal horns, temporal tip dilation , rounded 3rd but normal 4th ventricles?
Non-communicating
What is treatment for hydrocephalus?
Shunt - commonly ventriculoperitoneal shunt
What is the classical presentation of normal pressure hydrocephalus?
- elderly
- present with Hakim’s triad (wet, wobbly and weird)
What are the 3 symptoms of Hakim’s triad?
- abnormal gait
- urinary incontinence
- dementia
What is thought to be the cause of normal pressure hydrocephalus?
possibly decreasing brain elastance i.e. stiff tissue
What are investigations for normal pressure hydrocephalus?
- LP
- lumbar drain test
- lumbar infusion studies
What is treatment for normal pressure hydrocephalus?
- VP shunt
- medium-low or low-pressure valve
