ICP and Hydrocephalus Flashcards
What are the components of the ICP?
Brain = 1300-1750ml (80-85%), consists of tissue, intracellular fluid and extracellular fluid Blood = 100-150ml (5-8%) CSF = 100-150ml (8-12%)
What is the ICP?
Pressure exerted by the cranium onto brain tissue, CSF and intracranial circulating blood volume
Does the ICP stay constant?
Nope, constantly fluctuating = about 7-15mmHg at rest, can be negative in vertical position
What are the immediate mechanisms for compensating for an expanding mass in the cranium?
Decrease in CSF volume by moving it out of foramen magnum
Decrease in blood volume by squeezing sinuses
What is the delayed mechanism for compensating for an expanding mass in the cranium?
Decrease in extracellular fluid
What is the flow of CSF?
Choroid plexus - ventricular system - subarachnoid space - venous system
How is the cerebral perfusion pressure calculated?
CPP = MAP - ICP
How is the cerebral blood flow calculated?
Cerebral perfusion pressure/cerebral vascular resistance
Remains constant over wide range of BP
How is the cerebral blood flow autoregulated by pressure and metabolic factors?
Pressure = arterioles dilate/constrict in response to changes in blood pressure or ICP Metabolic = arterioles dilate in response to chemicals
What effect does increased CO2 have on cerebral blood flow?
Increased blood pressure and cause vasodilation = increases cerebral blood flow
What is the mechanism of autoregulation of the cerebral blood flow?
Unknown = direct reaction of smooth muscle to stretch, action of metabolic by-products or action of perivascular nerves
What are the four main reasons for increased ICP?
Mass effect, brain swelling, increase in central venous pressure or problems with CSF flow
What are some causes of a mass effect in the brain?
Tumour, infarct, contusions, haematoma, abscess = distort surrounding brain
What are some causes of brain swelling?
ischaemia, acute liver failure, encephalopathy, IIH, hypercarbia = decrease cerebral perfusion pressure but cause minimal tissue shift
What are some causes of increased central venous pressure?
Venous sinus thrombosis, heart failure or obstruction of jugular veins
What are the different ways CSF flow can be disrupted?
Obstruction = masses, Chiari syndrome
Increased production = choroid plexus papilloma
Decreased absorption = SAH, meningitis, malignant meningeal disease
What are the normal range of values for ICP?
Adults = 7-15mmHg
Older children = 10-15mmHg
Young children = 3-7mmHg
Newborns = 1.5-6mmHg (often <0)
What are the early signs of raised ICP?
Decreased level of consciousness and headache
Pupillary dysfunction +/- papilloedema
Changes in vision and nausea/vomiting
What are the late signs of raised ICP?
Coma, hemiplegia, fixed dilated pupils, bradycardia, hyperthermia and increased urinary output
What are the aims of interventions for raised ICP?
Maintain cerebral perfusion pressure and prevent ischaemia or brain compression
What are some non-medical interventions for raised ICP?
Maintain head in midline to facilitate blood flow and elevate head of bed to 30-45%
Maintain fluid balance, normal electrolytes and normocarbia
What is the medical management of raised ICP?
Use diuretics = mannitol, hypertonic saline, furosemide
May give anti-epileptics for seizure or barbiturate for coma
Surgery = decompression, remove mass lesions, CSF diversion
What are the different classifications of hydrocephalus?
Communicating vs non-communicating
Congenital vs acquired
What are some features of normal pressure hydrocephalus?
Idiopathic disease of elderly
Hakin’s triad = abnormal gait, urinary incontinence, dementia
May be due to decreasing brain elastance
What are the differentials of normal pressure hydrocephalus?
Other forms of dementia, cervical myelopathy, all urinary problems, Parkinson’s disease, depression
What investigations are done for normal pressure hydrocephalus?
Lumbar puncture, lumbar drain test and lumbar infusion studies
How is normal pressure hydrocephalus treated?
VP shunt, medium-low or low pressure valve
What is the epidemiology of idiopathic intracranial hypertension?
Women of child bearing age = Western world, overweight
Aetiology = CSF imbalance, oestrogen, transverse/sigmoid sinus stenosis
What are the symptoms of idiopathic intracranial hypertension?
Headache, double vision, blurring, tinnitus, radicular pain and papilloedema
No ventricular dilation
25% develop severe or permanent visual loss
What are the differentials of idiopathic intracranial hypertension?
Any other type of headache
Any other reason for raised ICP
Cervical radiculopathy
What investigations cane be done for idiopathic intracranial hypertension?
Lumbar puncture, CT or MRI of head, CTV, fundoscopy
What is the treatment of idiopathic intracranial hypertension?
Weight loss, diuretics or ONSF Carboanhydrase inhibitors (acetazolamide, topiramate) CSF diversion = LP or VP shunt Interventional radiology = intracranial venous sinus plasty or stenting
