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Advanced Principles of Anesthesia > Week 2 - Neurosurgery / Stereotactic Neurosurgery and Sitting Craniotomies > Flashcards

Week 2 - Neurosurgery / Stereotactic Neurosurgery and Sitting Craniotomies Flashcards

1
Q

What should be included in the preop evaluation for neurosurgery?

A
  • Assess intracranial compliance (signs/symptoms of increased ICP – review CT)
  • Know features/location of the mass – vascular lesion? infiltrating lesion? surrounding edema?
  • Assess Electrolytes – imbalances common (fluid restriction, diuretics & steroids, central endocrine abnormalities
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2
Q

What are the features of a normal head CT?

A

Symmetrical Structures

Ventricles Midline (appropriately sized)

No Compression (gray/white matter differentiation)

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3
Q

What are preop anesthetic considerations for neurosurgery?

A
  • Preop sedation?? – be very careful, rarely indicated
  • increased likelihood of resp depression –> hypoxemia/hypocapnia
  • Pharmacological interventions if indicated (steroids, diuretics, anticonvulsants)
  • Monitors as indicated (a-line, second PIV, foley, central line)
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4
Q

Why are steroids given in neurosurgery cases?

A

Improve viscoelastic properties of intracranial space within 24 hrs (reduce vasogenic edema associated tumors within 48 to 72 hrs)

  • started at least 48 hours prior to tumor extirpation
  • continued intra and postoperatively to maintain effects achieved preoperatively

*Studies in head injury patients show mixed results – Recent clinical trials—not recommended in moderate to severe TBI

• Dexamethasone most common – 10mgIVq6hrs

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5
Q

Why are diuretics given in neurosurgery cases?

A

Reduce intra and extracellular fluid compartments
-osmotic diuresis preferred to loop diuretics— mannitol has faster effects — 0.25 – 1.5 g/kg (larger doses have prolonged effects)

Mannitol and Furosemide may be used in combination
– Mannitol draws fluid out of brain
– Furosemide hastens intravascular water excretion
– Furosemide blocks neuronal chloride channels – Possibly preventing rebound swelling
– Furosemide reduces CSF production

*Studies show hypertonic saline (23%) boluses more effective than mannitol in reducing ICP

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6
Q

Why are anticonvulsants given in neurosurgery cases?

A
  • Acute cortical irritation can result in seizures (Head injury, Subarachnoid blood, Cortical incisions, Brain retraction)
  • Seizures increase CMRO2 increase CBF & ICP
  • Reduce the incidence of pre and postoperative seizures
  • Phenytoin (Dilantin) ???
  • Keppra now most popular ! 1 Gram IV with induction
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7
Q

What are the goals of induction during a neurosurgery case?

A

Smooth induction without increases in ICP or compromise of CBF

Avoid: HTN, HoTN, Hypoxia, Hypercarbia, Coughing/Bucking/Straining

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8
Q

What factors promote brain relaxation?

A
  • Adequate oxygenation (prevents cerebral vasodilation)
  • Hyperventilation (promotes cerebral vasoconstriction)
  • Venous Drainage (HOB up as tolerated by surgeon, 30*)
  • Muscle relaxation (prevents movement, straining, bucking
  • Mannitol (0.25-1.5 g/kg IV)
  • Furosemide (10-20 mg IV)
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9
Q

What is the “Tight Brain” Checklist?

A
  • Pressures (Are the pressures controlled?) – Jugular venous pressure
  • Head rotation/neck flexion/direct jugular compression?
  • Head-up posture? – Airway Pressure
  • Obstruction/ bronchospasm/ straining/coughing/ pneumothorax? – PaO2/PaCO2
  • Arterial Pressure – Metabolic Rate (Is metabolic rate controlled?)
  • Pain/arousal/seizures?
  • Vasodilators (Are vasodilators in use?)
  • N2O/Volatiles/SNP/Calcium channel blockers?
  • Mass Lesions (Are there any unrecognized mass lesions?) – Blood/Air/N2O?
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10
Q

What are anesthetic considerations for the maintenance phase during neurosurgery?

A
  • Brain parenchyma devoid of pain fibers
  • Anesthetic requirements substantially lower than during craniotomy and dural opening
  • Limit anesthetic supplements to short acting agents to facilitate postoperative neuro exam
  • Volatile agents may be used to prevent awareness and hypertension
  • Maintain muscle relaxation (especially if in pins)
  • Continue hyperventilation (if indicated)
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11
Q

What are the indications for hyperventilation in a neurosurgery case? What is the target PaCO2?

A

Indications = high or uncertain ICP, improve condition of surgical field

PaCO2 28-32

  • institution and extent of hyperventilation should be discussed with the neurosurgical team
  • reduction in CBF is not sustained - duration 6-18hrs, brain HCO3 is reduced and pH normalized
  • hypocapnia (PaCO2 <20?) induced cerebral ischemia – pH related alteration in enzyme function, increased lactate formation, may worsen neurological outcome in head injury pts
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12
Q

How do barbiturates provide cerebral protection?

A
  • Most profound reduction in CMRO2
  • May improve outcome following focal or incomplete global ischemia
  • max effect during “electrical silence”
  • not compatible with goals for rapid, complete emergence
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13
Q

How does body temperature affect CMRO2?

A

CMRO2 varies directly with brain temperature — 7% per degree C

Avoid hyperthermia which increases CMRO2

-hypothermia trials in humans have not shown benefit in the context of aneurysm surgery

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14
Q

What are fluid and electrolyte management goals in neurosurgery?

A

Maintain euvolemia and slightly hyperosmolar state

  • Crystalloid administration
  • Maintain serum osmolarity at 305-320 mOsm – 0.9% NS (309 mOsm) may be preferred to LR (272 mOsm)
  • Colloids (5% Albumin)
  • Transfusion based on hematocrit and comorbidities
  • Monitor for hypokalemia, hyponatremia, hyperglycemia, marked hypersomolarity
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15
Q

What are anesthetic considerations for emergence during neurosurgery case?

A
  • Allow gradual normalization of ETCO2
  • Hypertension should be controlled – Adequate pain control (narcotics), Labetolol, Esmolol, Nitroprusside, Nitroglycerine
  • Reverse neuromuscular blockade – After head dressing is placed
  • Prompt wakeup without straining/coughing
  • Neuro exam in room preferable after wakeup
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16
Q

What are anesthetic considerations for tumors?

A

Vary depending on location:

  • supratentorial
  • pituitary
  • posterior fossa

Tumor Type:

  • vasculatiry
  • invasiveness
  • location
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17
Q

What are common tumor types and locations?

A

Primary (50%):

  • Gliomas (most common and also the worst) – astrocytoma, brainstem glioma, ependymomas, optic nerve glioma, oligodendroglioma
  • Meningiomas
  • Schwannomas
  • Medulloblastomas
  • Craniopharyngiomas

Metastatic (50%):
-Lung, Breast, Colon

18
Q

What are the anesthetic considerations for Supratentorial tumors?

A
  • Potential for blood loss (Larger tumors, Invasive tumors, Tumors encroaching on sagittal sinus)
  • Low risk for VAE unless tumor near sagittal sinus – Full VAE precautions for tumors near posterior half of sagittal sinus
  • Craniopharyngioma (dissection around hypothalamus) – Sympathetic responses-hypertension, Diabetes insipidus (2-24 hours postop)
  • Frontal lobe involvement/subfrontal approaches – Delayed awakening
  • Gliomas and meningiomas are most frequent tumor types
  • most common neurosurgical procedure
19
Q

What are the anesthetic considerations for a Transphenoidal Hypophysectomy for a Pituitary tumor?

A
  • Tumors within sella turcica/suprasellar extension
  • ICP usually not issue d/t small tumor size
  • Oral RAE tube preferred
  • Hyperventilation – To reduce arachnoid bulging into sella turcica
  • Major bleeding – 2 large PIVs
  • A-line not usually necessary???
  • Throat packs/nasal packs intra-op
  • Smooth emergence vital!!!
20
Q

What endocrine abnormalities are seen with pituitary tumors?

A

Nonfunctioning/Nonsecretory Tumors:

  • compression/mass effect - panhypopituitarism; SIADH
  • adrenal insufficiency - hypocortisolism (steroid replacement)

Functioning Adenoma:

  • prolactin secreting amenorrhea; galactorrhea; hypogonadism, ACTH secreting hypercortisolism
  • GH secreting acromegaly; giantism; glucose intolerance

Diabetes Insipidus:

  • usually occurs 4-12 hrs postop – rare intraop
  • polyuria with rising serum osmo + declining urine osmo (specific gravity <1.002)
21
Q

What is stereotactic neurosurgery?

A
  • Involves 3D mapping using a coordinate system (Fiducials placed on scalp to guide/arrange coordinates)
  • MRI and CT scans and 3D computer workstations allow neurosurgeons to accurately target any area of the brain in stereotactic space
22
Q

When is stereotactic surgery utilized?

A

Deep Brain Stimulator placement – Parkinson’s

Epilepsy focus ablation

Brain biopsy

23
Q

What are the anesthetic considerations for stereotactic surgery?

A
  • Performed through burr hole in skull – analgesia via local injection at incision site
  • Usually done awake +/- sedation
  • Awake techniques require cooperative pt
  • Always check with surgeons before giving any sedatives
  • Avoid benzodiazepines for seizure focus ablation
  • Precedex (0.1-0.3 mg/kg/hr) popular
  • Potential difficult airway due to the stereotactic frame
24
Q

What are the indications for an awake craniotomy?

A

Performed for seizure focus mapping or tumor removal

  • “eloquent” cortex if removed results in the loss of sensory processing o linguistic ability, minor paralysis, or paralysis
  • left temporal or frontal lobes – speech and language
  • bilateral occipital lobes – vision
  • bilateral parietal lobes – sensation
  • bilateral motor cortex – movement

Minimizes chance of healthy brain injury (need cooperative, motivated pt

25
Q

What are the goals for an awake craniotomy?

A

Mapping of the eloquent areas:
– Ojemann stimulator used to map areas of aphasia and anomia.
– Pictures on a computer screen
– Stimulate the brain
– Talk to the patient / Say name, abc’s, etc
– This may take hours to do correctly
– Need an awake, cooperative, motivated patient

Surgical resection of ALL tumor without removal of ANY eloquent area

26
Q

What are preop considerations for an awake craniotomy?

A

Good patient education is a must!

  • Sights, sounds, smells, what to expect, need to stay still
  • Uncomfortable positioning -Mayfield (PINS)
  • Local injections by the surgeon
  • Drilling of the cranium (really loud and transmitted directly—disturbing to patient)
  • Removal of the bone flap – separating the meninges from the bone, potential for bleeding, can be very painful, unable to localize or induce at this point
27
Q

What are intraop considerations for an awake craniotomy?

A
  • Possibly/Rarely induce GETA for monitor placement and drilling and bone separation?
  • Dexmedetomidine, Remifentanil, Ondansetron, Propofol – LMA??
  • Patient emerged once the bone flap is being removed
  • Position patient for maximal comfort, reassure patient, provide light and air to patient, ability of patient to see Anesthetist
28
Q

What are potential intraop complications during an awake craniotomy?

A

Seizure Resection Surgery:

  • prophylaxis, check drug levels
  • is this typical seizure like activity for this pt?
  • is it focal or consistent with preop report?
  • is it progressing to grandmal?
  • does the pt have a reported aura?

Tumor Resection Surgery

  • seizure prophylaxis (keppra, DpH)
  • treat if they occur (surgeon preference)

Don’t want seizures – treatment may interfere with mapping and prolong procedure, wait for surgeon to request medication for treatment

*If seizure occurs – Propofol 10-20 mg – if continues 100-200mg

29
Q

What are the CV effects of Precedex?

A

Decreased HR

Decreased SVR

Indirectly decreased CO, SBP, and Contractility

30
Q

What are the pulmonary effects of Precedex?

A

Decreased minute ventilation but maintains CO2

31
Q

What is the anesthetic premedication dose of Precedex?

A

0.33 - 0.67 mcg/kg 15 min before surgery

  • decreases induction agent dose
  • decreases MAC
32
Q

What is the anesthetic MAC dose of Precedex?

A

1 mcg/kg over 10 minutes – bolus rarely given

  1. 7 mcg/kg/min keeps BIS 70-80
    - slower onset and offset than propofol - similar cardiorespiratory effects
33
Q

What are anesthetic considerations for a DBS for Parkinson’s?

A
  • Typically NO meds the morning of surgery
  • Frame placed preoperatively – Surgeon uses local
  • CT and MRI guided imaging
  • Presents to OR w/ frame in place – Almost impossible to manipulate airway. BE PREPARED!!!!!!
  • Beware of increased sensitivity to anesthetic agents
  • Beware of Parkinsons symptoms – when stimulating, tremors are much better, when off, tremors markedly worse (No meds!)
  • Beware of venous air embolus
  • Good communication w/ surgeons about level of consciousness
34
Q

What do you need to beware of during the postop management of DBS for Parkinson’s?

A
  • Beware of hemiplegia
  • Beware of seizures
  • Beware of excessive post op pain
  • Plan on admission and close neuro monitoring for at least 24 hours
35
Q

What are the two stages of DBS for Parkinson’s?

A

1st Stage = placement of wires in the brain

2nd Stage = placement of generator

  • usually 2 weeks after electrode placement
  • typically GETA
  • can be discharged home the same day
36
Q

What are the indications for a sitting craniotomy?

A

Posterior Fossa Pathology

-improved surgical access to posterior – midline structures (brainstem, floor of 4th ventricle, pontomedullary junction)

  • Sitting position is less prominent than it used to be
  • BEWARE of venous air embolus
37
Q

What does the positioning look like during a sitting craniotomy?

A

More often modified recumbent position – much like a beach chair position with head flexed forward in pins

Keep legs as high as possible – promotes venous return to heart, minimizes hemodynamic alterations

Slow and incremental positioning – minimizes hemodynamic alterations

Head holder must be attached to upper half of table and secured tightly – allows rapid flattening of bed

38
Q

What are the benefits of sitting position for a craniotomy?

A
  • Less blood loss (Lower arterial pressure – less arterial bleeding, Negative venous pressure – eliminates venous oozing)
  • Better surgical access (Less brain swelling / less blood in surgical field)
  • Better airway access (Prone position makes airway manipulation almost impossible, Improved chest excursion monitoring, ETT adjustment if necessary)
  • Improved cerebral drainage (gravity dependent) – Blood and CSF
  • Cranial Nerve Preservation
39
Q

What are complications of sitting position for a craniotomy?

A
  • Cardiovascular instability (Posterior fossa)
  • Respiratory compromise (Posterior fossa)
  • Hemodynamic instability
  • Pneumocephalus
  • Venous air emboluls
  • Paradoxical air embolus
  • Paraplegia (rare)

*complications associated occur more than in other positions

40
Q

What is the pathophysiology for an acoustic neuroma?

A

Benign tumor arising from the Schwann cell sheath of CN VIII

Vestibular Division >95%
Cochlear Division <5% — affects hearing/balance, encapsulated mass that is attached and cannot be separated from the nerve

*Linked with the genetic disorder Neurofibromatosis Type II – autosomal dominant syndrome

41
Q

What are the signs and symptoms of an Acoustic Neuroma?

A
  • Vertigo/Dizziness
  • Hearing loss
  • Tinnitus
  • Headache
  • Loss of balance
  • Visual problems
42
Q

What are anesthetic considerations for Acoustic Neuromas?

A
  • Take hearing loss into account – approach pt from unaffected side
  • Standard Monitors
  • A line and large bore IV (potential for blood loss, hemodynamic monitoring)
  • CO2 25-30 per surgeon request
  • Cranial nerve monitoring by surgical team
  • No intraop paralytics (short acting only if used)
  • NIMS Tube
  • Positioning (table rotated 180, arms tucked) – extreme table rotation
  • Ensure depth of anesthesia – pt cannot move
  • Plan on SNICU postop
  • Nausea is very common

Advanced Principles of Anesthesia (31 decks)

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