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CEREBROSPINAL FLUID AND INTRACRANIAL PRESSURE

PROBLEM BASED LEARNING (PBL)

PREPARED BY: MUHAMMAD ARIFF B. MAHDZUBBACHELOR MEDICINE AND SURGERY (MBBS)UNIVERSITY COLLEGE SHAHPUTRA, KUANTAN

The brain tissue is separated from the plasma by three main interfaces

(a) blood–brain barrier (BBB),

(b) blood–cerebral spinal fluid barrier (BCSFB)

(c) arachnoid cells underlying the dura mater.

CEREBROSPINAL FLUIDThe cerebrospinal Fluid [CSF] is a

clear, colorless transparent, tissue

fluid present in the cerebral

ventricles, spinal canal, and

subarachnoid spaces.

FORMATION CSF is largely formed by the choroid plexus of the lateral ventricle and remainder in the third and fourth ventricles.

About 30% of the CSF is also formed from the ependymal cells lining the ventricles and other brain capillaries (perivascular space).

MECHANISM OF FORMATION OF CSF

CSF is formed primarily by secretion (active transportation) and also by filtration from the net works of capillaries and ependymal cells in the ventricles called choroid plexus.

The resulting characteristics of the CSF are: Osmotic pressure approximately equal to that of plasma sodium ion concentration Approximately equal to that of plasma chloride ion About 15 per cent greater than in plasma potassium ion approximately 40 per cent less glucose 30 percent less

Rate of formation:

About 20-25 ml/hour

550 ml/day in adults. Turns over 3.7 times a day

Total quantity: 150 ml:

30-40 ml within the ventricles

About 110-120 ml in the subarachnoid space [of which 75-80 ml in spinal part and 25-30 ml in the cranial part].

ABSORPTION OF CSF THROUGH ARACHNOID VILLI

The arachnoidal villi are fingerlike inward projections of the arachnoidal membrane through the walls into venous sinuses.

The endothelial cells covering the villi have vesicular passages directly through the bodies of the cells large enough to allow relatively free flow of (1) cerebrospinal fluid, (2) dissolved protein molecules, and (3) even particles as large as red and white blood cells into the venous blood.

REGULATION OF ABSORPTION

• Absorption of CSF occurs by bulk flow is proportionate to CSF pressure.:• At pressure of 112 mm (normal average):

filtration and absorption are equal.• Below pressure of 68 mm CSF, absorption

stops

COMPOSITION OF CSF

Proteins(Less than plasma)=20-40 mg/100 mlGlucose( Less than plasma )=50-65 mg/100 mlCholesterol= 0.2 mg/100 mlNa+(more)= 147 meq/Kg H2OCl+(more) =Ca+(less) = 2.3 meq/kg H2OUrea(less) = 12.0 mg/100 mlCreatinine = 1.5 mg/100 mlLactic acid = 18.0 mg/100 ml

CHARACTERISTICS OF CSFNature:Colour = Clear, transparent fluidSpecific gravity = 1.004-1.007Reaction = Alkaline and does not coagulateCells = 0-3/ cmmPressure = 60-150 mm of H2O

CIRCULATION OF CSFLateral ventricle

Foramen of Monro [Interventricular foramen]

Thirdventricle

Subarachnoid space of Brain and Spinal cord

Fourth ventricle:

Cerebral aqueduct

Foramen of megendie and formen of luschka

FUNCTIONS OF CSFA shock absorberA mechanical bufferAct as cushion between the brain and craniumAct as a reservoir and regulates the contents of the craniumServes as a medium for nutritional exchange Transport hormones and hormone releasing factors

Count. Function Remove metabolic wastes from CNS Serves as pathway for pineal secretion to

reach the pituitary gland. it protects against acute changes in

arterial and venous blood pressure; it is involved in intra-cerebral transport,

ex. hypothalamic releasing factors

INTRACRANIAL PRESSURE • ICP typically means the supratentorial CSF

pressure measured in the lateral ventricles or over the cerebral cortex.

• Normal ICP value is 7-15 mm Hg

• Intracranial hypertension is defined as a sustained increase btwen20–25 mm Hg

MONORO-KELLIE HYPOTESIS

• The pressure-volume relationship between ICP, volume of CSF, blood, and brain tissue, and cerebral perfusion pressure (CPP) is known as the Monro-Kellie doctrine or the Monro-Kellie hypothesis.

• Since the cranium is a rigid structure with a fixed volume, comprising of CSF, brain, and blood. An increase in one of these components must be accompanied by an equivalent reduction in another to avoid a rise in ICP

• Initially, an increase in volume is met with little or no change in ICP. Ultimately, there is a point where minute increases in volume can result in a dramatic rise in ICP.

• Compensatory mechanisms that prevent the initial rise in ICP include:a) displacement of CSF from the cranial to spinal compartment,

b) decrease in production of CSF c) increase in absorption of CSF d) decrease in total cerebral blood volume

Absorption Of CSF

• Absorption of cerebrospinal fluid is mainly by arachnoidal villi

• Arachnoidal villi:– Microscopic fingerlike inward projection of

arachnoidal membrane through the walls and into venous sinus

– Allow relatively free flow of• CSF• Dissolved protein molecules• Particle as large as RBC & WBC