CEREBROSPINAL FLUID -PHYSIOLOGY

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CEREBROSPINAL FLUID

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PHYSIOLOGY OF CEREBROSPINAL FLUID :

PHYSIOLOGY OF CEREBROSPINAL FLUID Presenter: Dr.Nilesh Chandra

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Definition Physical characteristics Composition Formation and Circulation Flow and Absorption Regulation Clinical importance CSF- Discussion under the following subheadings

HISTORY:

HISTORY First report of existence of CSF – 17 th century B.C. Hippocrates – 4 th century B.C. Galen discovered ventricular cavities – 2 A.D. Vesalius – watery humour – 16 th century A.D. Magendie performed first tap of CSF in 1825.

What is CSF ?:

What is CSF ? Cerebrospinal fluid is an ultra filtrate of plasma, functioning as a hydraulic shock absorber. CSF is found in the ventricles of the brain and also in the subarachnoid space around brain and spinal cord.

FUNCTIONS :

FUNCTIONS Cushioning effect and protection - As brain floats in CSF, it protects brain from minor stress such as in jolting. - No protection from major stress like head injury. Mechanical bouyancy and support - CSF reduces the net weight of the brain from 1400g to 25g - This helps to increase the density of brain by not increasing its weight and thus preserving blood supply to lower zones of brain.

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Chemical protection – blood brain barrier. Nourishment and removal of metabolites Serves as a pathway for pineal secretion to reach pineal gland.

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Because of its easy access , it has diagnostic and therapeutic applications. Diagnostic - CSF analysis for detection of pathological conditions. Therapeutic – Central neuraxial block. Applications

Physical characteristics :

Physical characteristics Appearance – clear and colourless Volume :120 -150ml Specific gravity : 1.00010 – 1.00028 Rate of formation - ~ 550ml/day(0.35ml/min) CSF turnover : 3-4 ( 3.7 ) times/day CSF pressure : 60 – 150 mm H 2 0 / 70 – 180 mm CSF

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Volume of CSF : Adults Total - 120 to 150 ml Ventricles - 65 to 75ml Cisternal reservoir - 35 to 40ml Spinal SA space - 25 to 30ml Neonates – 10 to 60ml.(total CSF vol.) 80 to 100 mm H 2 0

Specific gravity of CSF:

Specific gravity of CSF 1.00010 to 1.00028 Relative to the CSF density, Local Anaesthetics are classified as hypobaric, isobaric and hyperbaric solutions. Density of CSF correlates with Peak sensory level of block Onset of block and duration of motor block indirectly.

COMPOSITION :

COMPOSITION COMPOSITION CSF PLASMA RATIO Protein(mg/dl) 15 - 45 6000 0.003 Glucose (mg/dl) 50 - 85 100 0.64 Chloride (meq/kg h 2 o) 113 99 1.14 Na + (meq/kg h 2 o) 147 150 0.98 K + (meq/kg h 2 o) 2.9 4.6 0.62 HCO 3 (meq/kgh 2 o) 25.1 24.8 1.01 P H 7.33 7.4 No. of cells 0-3 lymphocytes

FORMATION OF CSF :

FORMATION OF CSF 3 Sites : Choroid plexus ( 50 – 70 %) Ependymal surfaces of ventricles Perivascular spaces

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Choroid plexus projects into: temporal horn of lateral ventricle post. Part of 3 rd ventricle roof of 4 th ventricle

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Choroid plexus It is a cauliflower like growth of blood vessels covered by a thin layer of epithelial cells. It is made of 3 layers: fenestrated capillary endothelium extra cellular matrix epithelial cells

Mechanism of secretion :

Mechanism of secretion Transport across any epithelial surface 2 mechanisms transcellular transport paracellular transport Choroid plexus

Transcellular transport:

Transcellular transport

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BLOOD CSF Choroid plexus epithelium NET TRANSPORT 2K 3 Na CO 2 + H 2 O H 2 CO 3 H + HCO 3 HCO 3 Na Cl Cl Na Na Cl CA Na + –K + ATPase Na + – H + Exchange Na + – Cl - Cotransport Carbonic Anhydrase Furosemide Acetazolamide Glucose – Carrier mediated transport .

VIRCHOW ROBIN SPACE:

VIRCHOW ROBIN SPACE Virchow-Robin spaces , or enlarged perivascular spaces(EPVS) are spaces (often only potential) that surround blood vessels for a short distance as they enter the brain. Their wall is formed by prolongations of the pia mater. Functions Secretion of proteins site of entry of lymphocytes and macrophages in CSF

CIRCULATION OF CSF:

CIRCULATION OF CSF

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Movement of CSF is by : Pulsating blood vessels – helps in flow of CSF through their pulsations. Respiration – affects the central venous pressure – indirectly affects sagittal venous pressure – CSF absorption. Changes in posture – by indirectly affecting central venous pressure.

CSF ABSORPTION:

CSF ABSORPTION Bulk flow of CSF carries it through the subarachnoid space around and over the brain into arachnoid granulations

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ARACHNOID GRANULATIONS These are outpouchings of arachnoid mater that protrude into saggital venous sinus.

Factors affecting CSF ABSORPTION:

Factors affecting CSF ABSORPTION Site of absorption : - 4/5 th by cerebral arachnoid villi - 1/5 th by spinal arachnoid villi and along nerve sheaths into lymphatics. CSF absorption is passive and is dependent on higher CSF hydrostatic pressure than venous blood. Mean CSF pressure.(70 – 180mm CSF)

REGULATION :

REGULATION Effect of CSF pressure on formation and absorption of CSF. 0 0 0.4 0.8 1.2 1.4 FORMATION ABSORPTION 68 100 112 200 OUTFLOW PRESSURE ( mm of csf ) FLOW (ml/min) Formation is independent of CSF pressure At 112 mm CSF – formation is equal to absorption. At 68 mm CSF - absorption is zero.

Other Factors affecting CSF Synthesis :

Other Factors affecting CSF Synthesis Rate of CSF formation is decreased by: Alkalosis Drugs - Acetazolamide – CA inhibitor Furosemide – Na + Cl - cotransport inhibitor Cardiac glycosides – Na + K + ATPase inhibitor. Volatile anaesthetic agents – Enflurane and Desflurane increase CSF formation as a result of vasodilation of choroid plexus.

Clinical importance :

Clinical importance Why to study CSF in Anaesthesia? Pathological states associated with CSF pathways - Myeloceles , meningomyeloceles - Hydrocephalus Centralneuraxial block Critical care setup – Head injuries - infections – meningitis Neurosurgical procedures : Space occupying lesions, tumors, etc – altered cerebral hemodynamics – affect CSF formation, circulation and/ or absorption.

References:

References Anatomy for Anaesthesiologists – Harold Ellis, Stanley Feldman – 3 rd edition Textbook of Clinical Anatomy – Richard S Snell – 8 th edition Review of Medical Physiology- William F Ganong – 21 st edition. Textbook of Medical Physiology – Guyton and Hall – 11 th edition Textbook of Physiology (Excitable cells and Neurophysiology ) – Harry D Patton – 21 st edition Physiology of Spinal Anaesthesia – Nicholas M Greene – 3 rd edition Textbook of Anaesthesia – Miller – 7 th edition

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THANK YOU