15 - Raised ICP Flashcards
What is ICP determined by and what are the normal values for this?
- Volume of blood, brain and CSF all enclosed within a rigid box
How can we measure ICP?
- Lumbar puncture can be used to diagnose raised ICP and treat it
What is the Monro-Kellie Doctrine?
- Increase in 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
- e.g an intracranial mass, like a tumour, causes CSF and venous blood to be pushed out of the intracranial space as they are at the lowest pressure
- Due to skull being rigid plant pot
What is cerebral perfusion pressure?
CPP = MAP - ICP
Normal CPP >70 mmHg
Normal MAP ~90mmHg
Normal ICP ~10 mmHg
How does cerebral blood flow remain fairly constant despite changes in cerebral perfusion pressure?
- MAP increases then CPP increases, triggering cerebral autoregulation to maintain cerebral blood flow (vasoconstriction)
- ICP increases then CPP decreases, triggering cerebral
autoregulation to maintain cerebral blood flow (vasodilatation)
- If CPP falls below 50mmHg cerebral blood flow cannot be maintained as arterioles are maximally dilated
- Damage to brain can impair autoregulation
What are some signs and symptoms of raised ICP?
(first three on right are Cushing’s triad)
- Headache: constant, worse in the morning and on bending/straining?
- Nausea and Vomiting
- Difficulty concentrating/drowsiness
- Diplopia
- Focal neurological signs
- Seizures
What is Cushing’s reflex?
- Hypertension: rise in ICP so need rise in MAP to increased CPP
- Bradycardia: increase in MAP detected by baroreceptors causing reflex bradycardia by increasing vagal activity (can cause stomach ulcers due to vagal activity)
- Irregular breathing: compression of brainstem respiratory centres by herniation
What are some causes of raised intracranial pressure in general?
- Too much blood within cerebral vessels
- Too much blood outside of cerebral vessels (haemorrhage)
- Too much CSF
- Too much brain
- Something else e.g tumour, cerebral abscess, idiopathic
What are some examples of pathology involving too much blood within or outside of cerebral vessels that lead to a raised intracranial pressure?
- Raised arterial pressure (malignant hypertension)
- Raised venous pressure (e.g IVC obstruction by lung tumour)
- Extradural, subdural, subarachnoid haemorraghe
- Haemorraghic stroke
- Intraventricular haemorraghe
Too much CSF can lead to a raised ICP, what are some causes of an increase in CSF?
- Congenital: cerebral aqueduct stenosis, neural tube defects, increased CSF production or decreased CSF absorption
- Acquired: meningitis, trauma, post subarachnoid haemorraghe, tumours compressing ventricular system like cerebral aqueduct
What are some clinical signs of congenital hydrocephalus?
- Bulging head with head circumference increasing in diameter faster than expected
- Sunsetting eyes (compression of orbit and midbrain occulomotor)
How is hydrocephalus managed?
Acute:
- Tap fontanelle with needle
- External ventricular drain (risk of infection and need to be inpatient but good if shunt doesn’t work and allows continuous monitoring)
Long-Term
- VA or VP shunt with valve to stop backflow (can be vulnerable to abdominal infections and may need surgical revision)
What are the pathophysiological mechanisms of cerebral oedema?
- Vasogenic (breakdown of tight junctions)
- Cytotoxic (damage to brain cells)
- Osmotic (if CSF hypotonic)
- Interstitial (flow of CSF across ependyma into BBB)
How does idiopathic intracranial hypertension (IIH) present?
- May present with headache and visual disturbance
- Usually middle aged obese females?
- Can be confirmed by raised opening pressure on LP
- Treat with weight loss and blood pressure control
What do you need to do before you perform a lumbar puncture?
- Make sure there are no signs of intracranial pathology in a patient with suspected raised ICP as this can precipitate brain herniation
What are the different types of herniation that can occur when there is a raised intra-cranial pressure?
- Tonsilar (coning - compresses medulla as cerebellar tonsils forced through foramen magnum)
- Subfalcine (cingulate gyrus pushed under falx cerebri, ACA can be compressed as passes over CC)
- Uncal (uncus goes through tentorial notch compressing midbrain, CNIII palsy and possible contralateral hemiparesis due to compression of the cerebral peduncles)
- Central downward herniation (medial temporal lobe down tentorial notch)
- External herniation through skull fracture or craniotomy
How do we manage acute raised ICP to protect the brain?
- Airway and Breathing: maintain oxygenation and removal of CO2
- Circulatory Support: maintain MAP and therefore CPP (avoid hypotension)
- Sedation, Analgesia and Paralysis: decrease metabolic demand and prevent coughs that may increase ICP further
- Head up tilt/Head of Bed elevation: improve cerebral venous drainage
- Temperature: prevent hyperthermia, therapeutic hypothermia might be beneficial
- Anticonvulsants: prevent seizures and reduce metabolic demand
- Nutrition and PPIs: improve injury healing and prevent stomach ulcers due to increased vagal activity
How can we lower ICP after we have carried out brain protection measures?
- Mannitol or hypertonic saline (osmotic diuresis) then rehydrate orally
- Ventricualr drainage
- Decompressibe craniectomy (last resort)
What are the two phases of the Monro-Kellie doctrine?
When should you perform an urgent CT head?
How can you tell if a subdural haemorraghe visible on CT is chronic or acute?
- Will appear much darker if chronic
- Less midline shift if chronic so neurological abnomalities may not be present
What is the Chiari malformation?
Downward displacement of the medulla, fourth ventricle and cerebellum into the cervical spinal canal, as well as elongation of the pons and fourth ventricle.
This type occurs almost exclusively in patients with myelomeningocele
What is an anoxic brain injury?
Occurs when the brain is depleted of oxygen
What is the criteria for brain death?
