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Physiology of the Cerebrospinal Fluid and Intracranial Pressure

Physiology of the Cerebrospinal Fluid and Intracranial Pressure. Chapter 10 Presentation: S. Bahram Seif, Resident of Neurosurgery Isfahan University of Medical Sciences. Protective and Homeostatic Systems of the CNS. Skull Bones ( physical protection )

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Physiology of the Cerebrospinal Fluid and Intracranial Pressure

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  1. Physiology of theCerebrospinal FluidandIntracranial Pressure Chapter 10 Presentation: S. Bahram Seif, Resident of Neurosurgery Isfahan University of Medical Sciences

  2. Protective and Homeostatic Systems of the CNS • Skull Bones (physical protection) • CSF(hydraulic shock absorption) • Continuous Turnover of Extracellular Fluid (substrate supply and cellular homeostasis) • BBB

  3. Protective Systems can Become Detrimental

  4. Elevated ICP • Congenital lesions • Neoplasms • Metabolic syndromes • Infectious syndromes • Infarction • Hemorrhage • Trauma

  5. HISTORICAL CONSIDERATIONS • Galen • Hippocrates • Early Egyptian physicians Removing Pieces Of Skull

  6. 19th Century • Alexander Monro • George Kellie Monro-Kellie Doctrine

  7. Lumbar Puncture • 1911 • Quincke • 1951 continuously ICP monitoring • Lundberg

  8. NORMAL INTRACRANIAL PRESSURE • Upper limit of normal ICP: 15 mmHg • Usual range is 5 to 10 mmHg • Coughing or Sneezing: 30 to 50 mmHg

  9. mmHg x 1.36 = cmH2O

  10. ICP Evaluation • Intraventricular • Intraparenchymal • Subdural • Epidural

  11. CSF Pulsatility • Associated with Cardiac andRespiratoryactivity • Changes in these pulsatile components can be one of the earliest signs

  12. Cardiac Component • Left ventricular contraction • Peripheral arterial pulse • Choroid plexus and pial arteries • High-compliance venous blood vessels

  13. Respiratory Component • Generated by pressure changes in the thoracic and abdominal cavities

  14. Percussion wave (WI), the most constant, Pulsations in large intracranial arteries. • Tidal wave (W2), brain elastance. • Dicrotic wave (W3), dicrotic notch in the arterial.

  15. ICP is synonymous with CSF Pressure

  16. Atmospheric pressure • Hydrostatic pressure • Filling pressure

  17. As volume is added there are two principal routes for compensation

  18. Distention of the spinal dura mater • Displacement of CSF and blood

  19. ICP depends on the total volume inside the skull

  20. Intracranial Space: 1500-mL • 87%: the Brain • 9%: CSF (ventricles, cisterns, and subarachnoid space) • 4%: blood

  21. CSF • Compartmental • Extracellular space 164.5 mL

  22. CSF Production • Choroid plexuses • Ventricular ependyma

  23. Choroid Plexuses • Invaginations of the pia mater into the ventricular cavities Roofs of the third and fourth ventricles Walls of the lateral ventricles

  24. Energy-dependent secretion and reabsorption processes • 0.35 to 0.37 mL/min

  25. Higher sodium, chloride, and magnesium • Lower potassium, calcium, urea, and glucose • Similar osmolality

  26. Peak Production Rates Late evening Early morning

  27. CSF Drainage • Dural Venous System Even in CSF pressures of less than 5 mm Hg

  28. NPH • Ventricular enlargement • Absence of elevated ICP

  29. Gait disturbance • Dementia • Incontinence

  30. Lumbar Pressures: 6 to 24 cm H2O.

  31. Symptoms and Signs of ElevatedIntracranial Pressure • Depends greatly on the nature and anatomic location of the underlying pathologic condition • Headache, vomiting and papilledema.

  32. Cranial nerve palsies may arise as a result of pressure on brainstem nuclei (particularly abducens palsies)

  33. Papilledema • Reliable • Objective • Good specificity • Sensitivity: observer dependent

  34. Vital Sign Changes • Cushing response: Arterial Hypertensionand Bradycardia

  35. CPP = MAP - ICP

  36. Abnormal Respiration • Cheyne-Stokes: diencephalic region • Sustained hyperventilation: midbrain and upper pons • Slow respiration: Midpontine • Ataxic respirations: pontomedullary lesions • Rapid shallow breathing: upper medullary lesions

  37. Herniation Syndromes • Most serious complication of raised lCP

  38. Central Syndrome • Progressive dysfunction of structures in a rostral to caudal direction • 1st Diencephalic Structures: Change in behavior or even loss of consciousness, Cheyne-Stokes respiration • Pupils :small, with a poor reactivity • Contralateral hemiparesis • Pupils fall into a midline fixed position

  39. Uncal Syndrome • Unilaterally dilated and poorly reactive pupil • External oculomotor ophthalmoplegia • Ipsilateral hemiparesis: pressure on the contralateral cerebral peduncle on the edge of the tentorium cerebelli

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