Raised intracranial pressure Flashcards
What determines normal ICP?
- Determined by volume of blood, brain and CSF, also enclosed in a rigid box
What are the normal values for ICP?
- Adults 5-15 mmHg
- Children 5-7 mmHg
- Term infants 1.5-6 mmHg
- A good rule of thumb is that a pressure >20 mmHg is raised
What is the Monro-Kellie doctrine?
- Any increase in the volume of one of the intracranial constituents (brain, blood, or CSF) must be compensated by a decrease in the volume of one of the others
What happens in the case of an intracranial mass?
- The first components to be pushed out of the intracranial space are CSF and venous blood, since they are at the lowest pressure
How do we calculate cerebral perfusion pressure?
- Mean arterial pressure - ICP
- Normal CPP >70 mmHg
- Normal MAP ~90 mmHg
- Normal ICP ~10 mmHg
What happens when mean arterial pressure increases?
- Cerebral perfusion pressure increases
- Triggers cerebral autoregulation to maintain cerebral blood flow
- Vasoconstriction
What happens if ICP increases?
- Cerebral perfusion decreases
- Triggers cerebral autoregulation to maintain cerebral blood flow
Vasodilation
What happens if CCP is greater than 50 mmHg?
- Cerebral blood flow cannot be maintained as cerebral arterioles are maximally dilated
What happens to ICP as an intracranial mass expands?
- ICP can initially be maintained at a constant level up to a certain point
- After this point ICP will rise at a very rapid (exponential rate)
What can damage to the brain cause?
- Impairment or abolishment of cerebral autoregulation
What is Cushing’s reflex?
- A rise in ICP will initially lead to hypertension
- Bradycardia
- Irregular breathing
Why does a rise in ICP initially lead to hypertension?
- The body increases mean arterial pressure to maintain cerebral perfusion pressure
Why does an increase in ICP result in bradycardia?
- The corresponding increase in MAP is detected by baroreceptors which stimulate a reflex bradycardia via increased vagal activity (can cause stomach ulcers as a dangerous side effect)
Why does raised ICP result in irregular breathing?
- Continuing compression of the brainstem leads to damage to respiratory centres causing irregular breathing
What are the causes of raised ICP?
- Too much blood within cerebral vessels (rare)
- Too much blood outside of cerebral vessels (haemorrhage)
- Too much CSF
- Too much brain
- Something else e.g. tumour, cerebral abscesses, idiopathic
What causes too much blood within cerebral vessels?
- Raised arterial pressure (malignant hypertension)
- Raised venous pressure (SVC obstruction e.g. by a lung tumour)
What causes too much blood outside of cerebral vessels?
- Extradural
- Subdural
- Subarachnoid
- Haemorrhagic stroke
- Intraventricular haemorrhage
What are some causes of too much CSF?
- Hydrocephalus
- Acquired
What are the causes of hydrocephalus?
- Congenital (more common than acquired types)
- Obstructive e.g. neural tube defects, aqueduct stenosis
- Frequently part of a larger syndrome
- Communicating e.g. increased CSF production or decreased CSF absorption
What are the clinical signs of hydrocephalus?
- Bulging with head circumference increasing faster than expected
- Sunsetting eyes (due to direct compression of orbits as well as involvement of oculomotor nerve as it exits the midbrain)
How is hydrocephalus managed in the short term?
- Can be treated in the acute setting by tapping the fontanelle with a needle
How is hydrocephalus managed in the medium term?
- External ventricular drain
- Allows continuous pressure monitoring
- Can be at risk of infection due to direct communication between brain and outside world
- Requires inpatient monitoring so not good as a long term solution
- Used if shunt fails or contraindicated
How is hydrocephalus managed in the short term?
- Ventricular shunts
How are ventricular shunts inserted?
- A tube is placed from the ventricular system into the peritoneum (V-P) or right atrium (V-A)
- V-P shunts performed most commonly
- Tube is tunnelled under skin
- A one way valve is incorporated to prevent backflow into the ventricle
- Extra length of tubing is provided to allow growth before revision is required
What are V-P shunts vulnerable to?
- Infection
- Kinking
What are some acquired causes of hydrocephalus?
- Meningitis
- Trauma
- Haemorrhage
- Tumours compressing cerebral aqueduct
What are the four major pathologies of cerebral oedema?
- Vasogenic - breakdown of tight junctions
- Cytotoxic - damage to brain cells
- Osmotic - e.g. if ECF becomes hypotonic
- Interstitial - flow of CSF across ependyma and damage to BBB
What are the idiopathic causes of raised ICP?
- Idiopathic intracranial hypertension
Outline idiopathic intracranial hypertension
- May present with headache and visual disturbances
- Usually obese middle aged females
- Poorly understood aetiology
- Diagnosis confirmed by raised opening pressure on an LP
- Treat with weight loss and blood pressure control
Why do we need to make sure there are no signs of intracranial pathology before doing an LP in a patient with suspected ICP?
- This can precipitate brain herniation
What are the clinical features of hydrocephalus?
- Headache
- Nausea and vomiting
- Difficulty concentrating or drowsiness
- Confusion
- Double vision
- Focal neurological signs
- Seizures
What is headache caused by hydrocephalus like?
- Constant
- Worse in the morning
- Worse on bending and straining
What is double vision due to hydrocephalus like?
- Problems with accommodation (early sign)
- Pupillary dilation (late sign)
- May be effects on acuity
- Visual field defects
- Papilledema
What is tonsillar herniation?
- Cerebellar tonsils herniate through foramen magnum, compressing medulla
What is subfalcine herniation?
- Cingulate gyrus is pushed under the free edge of the falx cerebri
- Can compress anterior cerebral artery as it loops over the corpus callosum
What is uncal herniation?
- Uncus of temporal lobe herniates through tentorial notch, compressing adjacent midbrain
- Can cause third nerve palsy and maybe even contralateral hemiparesis (due to compression of cerebral peduncle)
What is central downward herniation?
- Medial temporal lobe /other midline structures pushed down through tentorial notch
How is hydrocephalus managed?
- Brain protection measures
- Other treatments
How do we protect the brain?
- Airway and breathing
- Circulatory support
- Sedation, analgesia and paralysis
- Head up tilt
- Temperature
- Anticonvulsants
- Nutrition and proton pump inhibitors
What are the airway and breathing brain protection measures used to treat hydrocephalus?
- Maintain oxygenation and removal of CO2
What are the circulatory protection measures used to treat hydrocephalus?
- Maintain mean arterial pressure and hence CPP
What are the sedation, analgesia and paralysis protection measures used to treat hydrocephalus?
- Used to decrease metabolic demand
- Prevents cough/shivering that might increase ICP further
Why do we do a head tilt in a patient with hydrocephalus?
- Improves cerebral venous drainage
Why do we need to control a patient’s temperature with hydrocephalus?
- Prevent hyperthermia
- Therapeutic hypothermia may be beneficial
Why does a patient with hydrocephalus need anticonvulsants?
- Prevent seizures
- Also need to reduce metabolic demand
Why does a patient with hydrocephalus need nutrition and PPIs?
- Improved healing of injuries and prevent stomach ulcers due to increased vagal activity
What are some other treatments of hydrocephaly?
- Mannitol or hypertonic saline (osmotic diuresis)
- Ventricular drainage
- Decompressive craniectomy as a last resort
