Principles of Neurosurgery

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mbrieger
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104927
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Principles of Neurosurgery
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2011-10-07 10:39:04
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Neurosurgery
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Principles of Neurosurgery chapter 2 Text
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  1. 3 intracranial contents
    • brain 1400ml
    • blood 150ml
    • CSF 150ml
  2. Vasogenic edema
    aka
    pathogenesis
    extracellular edema

    increased capillary permeability
  3. Cytotoxic Edema
    aka
    pathogenesis
    intracellular edema

    cellular swelling (neuronal, glial, endothelial)
  4. Interstitial Edema
    pathogenesis
    Increased brain water due to impairment of absorption of cerebrospinal fluid
  5. location of vasogenic edema
    mainly white matter
  6. location of cytoxic edema
    grey and white matter
  7. location of interstitial edema
    • transpendymal flow of CSF
    • periventricular white matter in hydrocephalus
  8. Composition of edema fluid in vasogenic edema
    plasma filtrate containing plasma proteins
  9. Composition of edema fluid in cytotoxic edema
    • incresed intracellular water and sodium
    • due to failure of membrane transport
  10. Composition of edema fluid in interstitial edema
    cerebrospinal fluid
  11. Extracellular fluid volume in vasogenic edema
    increased
  12. Extracellular fluid volume in cytotoxic edema
    decreased
  13. Extracellular fluid volume in interstitial edema
    increased
  14. pathologic lesion causing edema in vasogenic edema
    • primary or metastatic tumor
    • abscess
    • late stages of infarction
    • trauma
  15. pathologic lesion causing edema in cytotoxic edema
    • early stages of infarction (hypoxia)
    • water intoxication
  16. pathologic lesion causing edema in interstitial edema
    obstructive or communicating hydrocephalus
  17. vasogenic edema
    - effect of steroids
    - effect of manitol
    • effective
    • effective
  18. cytotoxic edema
    - effect of steroids
    - effect of manitol
    • not effective
    • effective
  19. interstitial edema
    - effect of steroids
    - effect of manitol
    • not effective
    • questionable
  20. Most significant factor determinining cerebral blood flow
    Cerebral Profusion Pressure
  21. CPP
    • blood pressure gradient across brain
    • MAP - ICP
  22. 3 major factors influencing cerebral blood flow
    • systemic blood pressure
    • CO2 and H+ concentration in arterial blood
    • O2 concentratino
  23. MAP
    diastolic pressure + 1/3 pulse pressure
  24. autoregulation
    ablility to maintain blood flow to brain at a wide range of MAPs, 50 to 160 mmHg
  25. Autoregulation
    Low MAP =
    cerebral arteriole dilation --> greater flow at decreased pressure
  26. Autoregulation
    increased systemic BP =
    arteriole constriction
  27. decreased O2 causes
    cerebrovascular dilation
  28. CO2 effects on brain
    cerebrovascular dilation
  29. hyperventilation
    decreases CO2, decreases dilation
  30. Normal ICP
    • 10 to 15 mm Hg
    • 136 to 204 mm H2O
  31. two major dural folds
    • falx cerebri - sickle shaped in midline
    • tentorium cerebelli - tent shaped
  32. common causes of increased ICP
    • Localized masses
    • Obstruction of CSF pathways
    • Obstruction of major venous sinuses
    • Diffuse brain edema or swelling
    • Idiopathic
  33. Localized masses include
    • Hematomas
    • Neoplasms
    • Abscesses
    • Focal edema due to trauma
  34. Obstruction of CSF pathways include
    Obstructive and communicating HCP
  35. Obstruction of major venous sinuses includes
    • depressed skull fractures damaging sinus
    • thromboembolic desease from contraception
  36. Diffuse brain swelling and edema occurs with
    • Encephalitis, meningitis
    • diffuse head injury
    • SAH
    • Reye's syndrome
    • Lead enxephalopathy
    • Water intoxication, fluid overload, near drowning
  37. idiopathic increased ICP
    pseudotumor cerebri
  38. cingulate herniation presentation
    no specific clinical signs or symptoms
  39. cingulate herniation
    - due to
    - herniation of
    - displaces what
    - compromisses what
    • due to supratentorial mass
    • herniation of cingulate gyrus across falx cerebri
    • usual displacement of ventricular system
    • ACA may be compromissed
  40. tentorial or uncal herniation
    presentation
    • impaired consciousness - compressed RAS
    • dilated ipsilateral pupil - compressed CNIII
    • contralateral hemiplegia - compressed cerebral peduncles
  41. tentorial or uncal herniation
    - prevalence
    - due to
    - herniation of
    • most common
    • due to middle cranial fossa mass
    • inferomedial temporal lobe herniation between rostoral edge and tentorial edge into posterior fossa
  42. central herniation
    - due to
    - displaces
    • due to masses far from tentorial hiatus such as frontal, perietal, or occipital
    • downward displacement of diencephalon and midbrain throu tentorial incisura
  43. central herniation
    presentation
    • not easily recognizable
    • bilaterally small reactive pupils
    • Cheyne stoke respirations
    • obtunded
    • loss of vertical gaze
  44. tonsillar herniation
    - due to
    - herniation of
    • due to acute expansion of posterior fossa lesions or (LP with increase ICP)
    • herniation of cerebellum tonsils through foramen magnum in to spinal canal, compressing medulla
  45. tonsillar herniation
    presentation
    • Cardiorespiratory impairment
    • Hypertension
    • High pulse pressue
    • Cheyne Stoke respirations
    • Neurogenic hyperventilation
    • Impaired consciousness
    • Stiff neck or in opisthotonic position
    • Decorticate or decerebrate posturing
  46. symptom and signs of increased ICP
    • HA with generalized location
    • HA worse at night and in recumbant position
    • Vomiting without nausea
    • Vomiting with neuro sign points to lesion
    • Papilledema
  47. two most common indications for ICP monitoring
    • closed head injury
    • SAH
  48. two most common ICP monitoring systems
    • intraventricular catheter connected to manometer and drainage system
    • fiberoptic transducer tipped catheter system placed within the ventricle, parenchyma, or subdural space.
  49. advantages to fiberoptic transducer tiped catheters
    • zero point does not require recalibration with differences in head position
    • not susceptable to blockage
  50. disadvantages to fiberoptic transducer tiped catheters
    • higher cost
    • inability to tunnel - thus higher rate of infx
    • baseline drift - less reliable over time
    • possible inaccuracies
  51. order of arterial waves reflected in normal ICP wave form
    • percussion wave
    • tidal wave
    • dicrotic notch
    • dicrotic wave
  52. increased ICP is reflected in the wave form as
    tidal waves or dicrotic waves of greater amplitude
  53. type A waves
    • due to abrupt elevation in ICP for 5 to 20 minutes
    • appear as plateau
    • may be marked by decread conciousness, restlessness, increased tone, tonic clonic movements
  54. B-waves
    • frequency of .5-2/min
    • related to rhythmic variations in breathing
  55. C waves
    • rhythmic variations related to Traub-Meyer Hering waves of systemic blood pressure
    • frequency of 6/min
  56. B and C waves
    have questionable clinicle significance.
  57. tx of increased ICP
    • removal of blood or mass cause
    • ventricular drainage
    • mannitol
    • hyperventilation
    • loop diuretics
    • steroids
    • barbituate coma
  58. ventricular drainage is particular effective with
    cerebral edema
  59. manitol
    • osmotic agent for tx of cerebral edema
    • by increasing serum osmolality it cause fluid in brain to be drawn from the parenchyma into the vascular space.
  60. normal serum osmolality
    275 to 290 mOsm/kg
  61. increase of how much will have significant effect on cerebral edema
    10 mOsm/kg
  62. administration of manitol
    • usually small boluses rather then continuous drip
    • 0.25g/kg at Q4 or 6
  63. additional effects of manitol
    • decrease in CSF production
    • increases in cerebral blood flow
    • increases cerebral oxygen consumption
    • decreases blood viscosity
    • (increases profusion)
  64. Mannitol's effectiveness
    48 to 72 hours then begins to leak from vesels
  65. hyperventilation
    • reduces ICP by reducing intracerebral blood flow and volume through vasoconstriction
    • used for acute management only
  66. in head injuries hyperventilation may not be the best choice because
    the brain is often under perfused and hyperventilation will decrease profusion further
  67. hyperventilation goals for acute condition
    pCO2 28 to 32 mm Hg
  68. loop diuretics
    • used in conjuction with manitol has synergistic effect on ICP
    • may reduce CSF production
  69. steroids
    dexamethasone is used for treating chronic issues with ICP - for example vasogenic edema from neoplasm
  70. steroids are ineffective with
    vasogenic edema from infarct or trauma
  71. steroids act by
    • stabilizing the cell membrane by inhibiting lysosomal activity
    • suppressing polyunsaturated fatty acid production
    • decreasing free radical production
  72. dosing of steroids
    • dexamethasone
    • loading dose of 10mg IV followed by 4mg Q6H.
    • after goal then taper over 3 to 4 days
  73. barbituate coma
    last resort in increased ICP managment
  74. barbituates decrease ICP by
    • scavenging free radicals from mitochondrial respiration
    • inhibiting cerebral metabolism and reducing cerebral blood flow
  75. barbituate dosing
    • thiopental
    • loading dose 3 to 10 mg/kg over 10min
    • maintenance dose of 1-2mg/kg/h
    • serum level mantained to 3-4mg/L
  76. pts under barbitute therapy require
    intensive monitoring of hemodynamic function, ICP, and blood gasses
  77. barbituates are withdrawn when
    • ICP normalizes
    • there is good intracranial compliance
  78. administered if pt becomes hypotensive with bartituates
    vasopressors

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