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Increased intra cranial pressure
Components of the cranium
1-Brain 80% of intracranial contents (1400ml) (70%brain and 10% interstitial fluid)
2-Blood 10% (150ml)
3-CSF 10% (150)
Increase in any intracranial component is compensated by decrease in the volume of the venous blood and CSF.
To maintain the pressure within physiologic range the venous system collapse easily squeezing venous blood through the jugular veins and through the emissary and scalp veins. CSF can be displaced through foramen magnum to the spinal subarachnoid space and the formation rate is decreased.
When this compensation is exhausted minute changes in volume produce significant increase in pressure.
Compliance: the change in volume observed for a given change in pressure
Elastance: the change in pressure observed for a given change in volume.
The blood Brain Barrier BBB
Not all substances in the circulation reach the neural structures, a barrier in the wall of the capillaries regulate the flow of biologically active substances into the brain and protect the sensitive neural tissues from toxic materials
Cerebral oedema
It is defined as increase in brain volume due to increase in its water content
Types
1-vasogenic (Extra cellular) oedema
The most common clinical type
- Pathogenesis: It results from increase permeability of the capillaries
- Site :occurs in the white matter
- Composition of oedema fluid :plasma filtrates contains plasma proteins
- Extracellular fluid volume :increased
- Causes: Tumors, abscess, late stage infarction, and trauma
2-Cytotoxic Oedema (intracellular)
- Pathogenesis: Results from hypoxia of the neural tissue this lead to accumulation of water intracellular with swelling of all cells.
- Site :occurs in the white and gray matter
- Composition of oedema fluid :water and sodium
- Extracellular fluid volume :decreased
- Causes: early stage infarction, and water intoxication.
3-Interstitial oedema
- Extracellular accumulation of fluid due to decrease CSF absorption
- Site :periventricular white matter
- Composition of oedema fluid: CSF.
- Extracellular fluid volume :increased
- Causes: hydrocephalus.
Cerebral blood flow
Normal CBF 50 -60 mL/100g brain tissue /min.
Cerebral perfusion pressure CPP
The effective blood pressure gradient across the brain, it is the difference between the incoming mean arterial blood pressure and the Intracranial pressure
With increase of the ICP the CPP decrease
Pathological effect of increased intracranial pressure
Normal ICP range from 10-15 mmHg (120 – 200mmH2O).
Increased ICP cause
- decrease CPP and this cause brain ischemia
2-focal mass can cause distortion and herniation of the brain