ricp 2 Flashcards
what is normal icp determined by
Determined by volume of blood, brain and CSF all enclosed within a rigid box
What is the range for normal icp? and what is a raise?
Values (wide range, can be difficult to define normality precisely)
Adults 5-15 mmHg
Children 5-7 mmHg
Term infants 1.5-6mmHg
A good rule of thumb is that a pressure >20 mmHg is raise
What is teh monro-kellie doctrine?
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
•In the case of an intracranial mass (e.g. brain tumour), the first components to be pushed out of the intracranialspace are CSF and venous blood, since they are at the lowest pressure
What is normal CPP?
Cerebral perfusion pressure •CPP = mean arterial pressure (MAP) – ICP •Normal CPP >70 mmHg •Normal MAP ~90mmHg •Normal ICP ~10 mmHg
Describe physiological responses to changes in map and icp
- If MAP increases then CPP increases, triggering cerebral autoregulation to maintain cerebral blood flow (vasoconstriction)
- If ICP increases then CPP decreases, triggering cerebral autoregulation to maintain cerebral blood flow (vasodilatation)
When does damage to the brain due to reduced cppoccur?
- If CPP <50 mmHg then cerebral blood flow cannot be maintained as cerebral arterioles are maximally dilated
- ICP can be maintained at a constant level as an intracranial mass expands, up to a certain point beyond which ICP will rise at a very rapid (exponential) rate
- Damage to the brain can impair or even abolish cerebral autoregulation
What is cushing’s triad?
Cushing’s triad aka Cushing’s response aka Cushing’s reflex
•A rise in ICP will initially lead to hypertension as the body increases MAP to maintain CPP
•The increase in MAP is detected by baroreceptors which stimulate a reflex bradycardia via increased vagal activity (which can cause stomach ulcers as a dangerous side effect)
•Continuing compression of the brainstem leads to damage to respiratory centres causing irregular breathing
What are causes of ricp in terms of “too much blood”
Too much blood within cerebral vessels (rare)
•Raised arterial pressure
oMalignant hypertension
•Raised venous pressure
oSVC obstruction (e.g. external compression by a lung tumour)
Too much blood outside of cerebral vessels (haemorrhage) •Extradural •Subdural •Subarachnoid •Haemorrhagic stroke •Intraventricular haemorrhage
What can cause raised icp in terms of too much csf?
Hydrocephalus. Congenital (more common) or Acquired: - Meningitis - Trauma - Haemorrhage (e.g. post subarachnoid haemorrhage) - Tumours (e.g. compressing cerebral aqueduct)
What are types of congenital hydrocephalus
Obstructive
•Neural tube defects
•Aqueduct stenosis
•Frequently part of a larger syndrome
Communicating (i.e. drainage of CSF not impaired)
•Increased CSF production
•Decreased CSF absorption
What are the clinical signs of congenital hydrocephalus
Clinical signs
•Bulging head 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 midbrain)
Describe acute management for congenital hydrocephalus
•Can be treated in acute setting by tapping the fontanelle with a needle
Describe medium term drainage for congenital hydrocephalus
Medium term drainage can be achieved by external ventricular drain (EVD)
o Allows continuous pressure monitoring
o Can be at risk of infection due to direct communication between brain and outside world
o Requires inpatient monitoring so not good as a long term solution
oUsed if shunt fails or contraindicated
Describe long term management of congenital hydrocephalus
Long term drainage by ventricular shunts
o Essentially, a tube is placed from the ventricular system into the peritoneum (V-P) or right atrium (V-A)
o V-P shunts performed most commonly#
o Tube is tunnelled under skin
o A one way valve is incorporated to prevent backflow into ventricle
o Extra length of tubing is provided to allow growth before revision is required
o V-P shunts vulnerable to infection (e.g. if abdominal infection, can track back up to brain) or kinking
o Most shunts will require revision
What are causes of ricp in terms of “too much brain”
cerebral oedema