Anesthesia for Neurosurgery

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Anesthesia for Neurosurgery
2014-01-19 11:24:15
BC Nurse Anesthesia CP2

Anesthesia for Neurosurgery
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  1. Hypercarbia causes vaso_____
  2. What is the benefit to cerebral blood flow with hyperventilation?
    Overall decrease in cerebral blood flow, ischemic areas are able to dilate to increase blood flow
  3. Inverse steal
    With hyperventilation or decreased metabolism, the ischemic areas dilate to redirect blood flow to the areas that need it
  4. What effect does decreased metabolism have on cerebral blood flow?
    Decreased blood flow
  5. ____ and ____ are coupled and both cause decreased cerebral blood flow
    Hyperventilation, decreased metabolism
  6. With hyperventilation, how does the PaCO2 respond?  How long does this last for?
    • Decreased PaCO2
    • Lasts for several days until the kidneys compensate
  7. With hyperventilation, how do CSF pH and CBF change?
    CBF decreases and CSF pH increases, but only for 6-8 hours.
  8. Why does the increase in CSF pH last only 6-8 hours?
    Due to active transport of bicarb ions out of the CSF (this is much faster than renal compensation)
  9. What 3 factors affect CBF?
    hypoxia, BP, and CO2
  10. CBF autoregulation
    CBF is maintained btw a MAP of 50-150 mmHg
  11. How does PaCO2 level affect CBF?
    Linearly, CBF increases by 1-2 ml/ 100 g brain tissue for each 1 mmHg increase in PaCO2
  12. How does PaO2 affect CBF?
    No effect on CBF until PaO2<60 mmHg, then CBF increases
  13. Normal ICP
    5-15 mmHg
  14. Intracranial HTN
    ICP > 20 mmHg
  15. CPP
    CPP = MAP - ICP
  16. In what 3 areas of the brain can we decrease volume to decrease ICP?
    • 1) CSF / ECF
    • 2) brain tissue
    • 3) blood
  17. With a noncompliant brain, how will increases in intracranial volume affect ICP?
    It will increase ICP
  18. How can the tissue compartment be manipulated to control ICP?
    Hematoma evacuation or tumor resection
  19. How can the venous blood compartment be manipulated to control ICP?
    Elevate HOB to facilitate jugular venous drainage, avoid increases in intrathoracic pressures as this inhibits venous drainage (PEEP, coughing)
  20. How can the arterial blood compartment be manipulated to control ICP?
    • Avoid high PaCO2 and hypoxia (increased blood flow)
    • Avoid volatiles
    • -Both increase CBF and thus increase ICP
    • Prevent seizures (increased metabolism and thus increased blood flow)
  21. How can the fluid compartment (CSF and ECF) be manipulated to control ICP?
    • Drain CSF (lumbar drain)
    • Diuretics
    • Steroids
  22. How do the volatiles affect CBF?  How long does their effect last for?
    • VD and thus increase CBF
    • 3 hours after exposure
  23. Which volatile agent causes the most increase in CBF?
    Halothane- 200% increase
  24. Rank the volatiles in order of VD potency
    • halo> enf> iso> des > sevo 
    • however the differences between iso, des, and sevo are likely not clinically significant
    • all are dose dependent
  25. How do the volatiles affect CMR?  Is this good or bad?
    • All decrease CMR
    • Decreased metabolic rate means decreased blood flow and counteracts the effect of VD
  26. Which volatile agent decreases CMR the least?
    Halo, thus the worst choice for a pt with increased ICP
  27. How does N20 affect CBF?  Is it safe to use for a pt with increased ICP?
    • N20 increases CBF due to its effect of stimulating the SNS and increasing CMR
    • Can be safely used as part of a balanced anesthetic
  28. What anesthetic technique is safest for a pt with high ICP?
  29. S/sx increased ICP
    H/A, CNS depression, confusion, somnulence, N/V, CT may show midline shift
  30. Overall goal in terms of drug selection for a pt with a "tight brain"
    With this in mind, what drugs should be avoided?
    • Prevent increases in CMR
    • Avoid ketamine, enflurane (lowers the seizure threshold), N20 alone
  31. Why is propofol an ideal drug for a pt with a "tight brain"?
    • Decreases CMR and thus decreases CBF and ICP
    • Etomidate does the same thing
    • Barbiturates and benzos are also helpful
  32. Can succ be used for a pt with increased ICP?
    Yes, but need to defasiculate first (fasiculations cause a transient increase in ICP)
  33. What factors can contribute to an increased metabolic rate and thus increased CBF?
    Pain, hyperthermia, seizures
  34. Supratentorial vs. infratentorial
    • Supra- front of the brain, not the brainstem
    • Infra- aka posterior fossa, near the brainstem
  35. Supra-tentorial tumor management
    • Control intracranial volume by:
    • avoiding coughing
    • prompt intubation
    • HOB elevated
    • euvolemia (possible diuretics)
  36. Concerns related to pre-medication for a pt with increased ICP?
    • Sedation may cause hypoventilation and increased PaCO2 and thus increased CBF
    • but…
    • Want to give enough to prevent anxiety and increased HR and metabolism
  37. Mannitol
    -type of diuretic
    • osmotic diuretic
    • 0.25 - 1 g / kg given over at least 10 minutes
  38. Goal PaCO2 level for an intubated pt with increased ICP
    35 mmHg
  39. What is one of the most stimulating parts of a craniotomy?  How should this part of the surgery be managed?
    • Pin placement 
    • Give fentanyl (CV stable)
  40. Crani anesthésia maintenance
    • Avoid hypervolemia
    • -Usually just replacing NPO deficit
    • -Isotonic fluids
  41. Why should D5W be avoided in crani pts?
    • 1) glucose is deleterious and further neuro injury
    • 2) glucose gets metabolized to free water which is hypotonic
  42. Usual position for a crani of the posterior fossa?  Major risk associated with this position
    • Sitting
    • VAE
  43. Advantages to use of the sitting position
    Better exposure, decreased bleeding
  44. T or F, sitting position is associated with increased M+M?
  45. Why is there a risk of VAE with the sitting position?
    • Surgical site is above the heart (risk anytime the surgical site > 5 cm above RA)
    • Venous sinuses are attached to the dura (open venous sinuses in the surgical site above the heart)
  46. HD effects of the sitting position
  47. Paradoxical air embolism
    -what is it?
    -what increases the risk?
    • Air travels from right side of heart to LA
    • PEEP slightly increases the risk
  48. Most sensitive method for detection of VAE?
    Most commonly used method?
    • Most sensitive= TEE
    • Most used= precordial doppler (2nd most sensitive method)
  49. Millwheel murmur
    Heard with precordial doppler when air enters the heart
  50. How does ETCO2 change with a VAE?
    How does ETN2 change?
    • ETCO2 will decrease due to air in pulmonary vessels
    • ETN2 will increase (dead space)
  51. Actions to take upon recognition of a VAE
    • Prevent more air from entering
    • -Tell the surgeon (s/he'll will pack and flood the surgical field)
    • -Apply jugular compression
    • -Lower HOB
    • Treat the intravascular air
    • -Aspirate CVP catheter to pull air out
    • -D/C N20
    • -FiO2 to 100%
    • -Pressors and CPR if needed
  52. How will BP change with a VAE
    Decreased BP due to decreased preload (air not blood is going to RA)
  53. T or F, M+M is increased for a pt in sitting position for a crani?
  54. Complications of posterior fossa surgeries
    • Macroglossia and airway obstruction
    • Extreme neck flexion can damage the SC
    • CN disturbances affecting respiratory and CV
  55. Pneumocephalus
    • Air entrained in the brain
    • Most often associated with posterior fossa cranis
  56. N20 use and posterior fossa craniotomy
    • Ok when cranium is open
    • Contraindicated when dura is being closed,
    • but due to post-op complication of tension pneumocephalus post-op (unrelated to N20 use), should just avoid N20
  57. T or F, the same principles for management of increased ICP apply to management of a posterior fossa crani?
  58. Hormones produced by the anterior pituitary?
    • GH
    • corticotropin
    • thyrotropin
    • prolactin
    • FSH
    • LH
  59. Hormones produced by the posterior pituitary?
    • ADH
    • oxytocin
  60. How are pituitary tumors typically dx?
    • Ammenorhea in F
    • Decreased libido in M
    • Both due to increased prolactin levels
  61. When is the transphenoidal approach appropriate for removal of a pituitary tumor?
    Tumor < 10 mm
  62. T or F, transphenoidal approach for removal of a pituitary tumor is not an intracranial procedure?
  63. Transphenoidal approach for removal of a pituitary tumor infection risk
    • High due to entering the surgical site via the nose
    • Abx very important
  64. Hunt and Hess classification 
    • Used to assess degree of SAH and assess prognosis
    • Used for cerebral aneurysm pts
  65. T or F, considerations for pts with a cerebral aneurysm are similar to those for pts with increased ICP
  66. Why are pre-op CVP and A line essential for a pt with a cerebral aneurysm?
    • BP control and IV volume
    • Major goal is to reduce IC volume
  67. BP control during aneurysmal clipping?
    What about during aneurysmal resection?
    • Clipping- high normal
    • Resection- low normal (if clip were to slip need to rapidly reduce BP so surgeon can visualize field and stop bleeding)
  68. Cerebral aneurysm rupture actions during rupture
    • Reduce blood flow
    • Nitroprusside
    • Ipsilateral carotid artery compression
    • Replace blood loss
    • 100% FiO2
  69. Cerebral aneurysm rupture actions after controlling hemorrhage
    • Cerebral preservation
    • Elevate BP
    • Reduce edema

    Control ventilation and monitor ICP
  70. Post-op vasospasm
    • R/t cerebral aneurysm repair
    • Prevented by triple H therapy
    • -hypervolemia (keep vessels full to prevent vasospasm)
    • -HTN
    • -hemodilution
    • -borderline high CO2 also helps to keep vessels full and prevent vasospasm
  71. Relative contraindications to induced hypotension
    • Ischemic CVA
    • CAD
    • hypovolemia
    • Anemia
    • Severe HTN
    • Extremes of age
  72. Complications of induced hypotension
    • Cerebral thrombosis or ischemia
    • Coronary artery thrombosis
    • Renal insufficiency
    • Hepatic failure
    • Increased bleeding at post-op site
    • Rebound hypertension
  73. For what procedure might induced hypotension be needed?
    Cerebral aneurysm rupture
  74. Pre-anesthesia assessment of the head injured pt
    • Airway (c-spine)
    • Breathing
    • Circulation
    • Associated injuries
    • GCS
    • Pre-existing chronic illness
    • Injury circumstances- timing, drugs or ETOH, duration of unconsciousness
  75. Clearing a c-spine
    X-ray and intact neuro exam
  76. Inline neck stabilization
    • Used for unstable c-spine to secure advanced airway
    • 3 people needed
    • 1- hold neck neutral
    • 2- cricoid pressure
    • 3- instrument the airway
  77. GCS 3 categories
    • Eye opening (max score of 4)
    • Verbal response (max score of 5)
    • Motor response (max score of 6)