Week 2 - Neurosurgery / Stereotactic Neurosurgery and Sitting Craniotomies Flashcards
(42 cards)
What should be included in the preop evaluation for neurosurgery?
- 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
What are the features of a normal head CT?
Symmetrical Structures
Ventricles Midline (appropriately sized)
No Compression (gray/white matter differentiation)
What are preop anesthetic considerations for neurosurgery?
- 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)
Why are steroids given in neurosurgery cases?
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
Why are diuretics given in neurosurgery cases?
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
Why are anticonvulsants given in neurosurgery cases?
- 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
What are the goals of induction during a neurosurgery case?
Smooth induction without increases in ICP or compromise of CBF
Avoid: HTN, HoTN, Hypoxia, Hypercarbia, Coughing/Bucking/Straining
What factors promote brain relaxation?
- 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)
What is the “Tight Brain” Checklist?
- 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?
What are anesthetic considerations for the maintenance phase during neurosurgery?
- 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)
What are the indications for hyperventilation in a neurosurgery case? What is the target PaCO2?
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
How do barbiturates provide cerebral protection?
- 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
How does body temperature affect CMRO2?
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
What are fluid and electrolyte management goals in neurosurgery?
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
What are anesthetic considerations for emergence during neurosurgery case?
- 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
What are anesthetic considerations for tumors?
Vary depending on location:
- supratentorial
- pituitary
- posterior fossa
Tumor Type:
- vasculatiry
- invasiveness
- location
What are common tumor types and locations?
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
What are the anesthetic considerations for Supratentorial tumors?
- 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
What are the anesthetic considerations for a Transphenoidal Hypophysectomy for a Pituitary tumor?
- 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!!!
What endocrine abnormalities are seen with pituitary tumors?
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)
What is stereotactic neurosurgery?
- 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
When is stereotactic surgery utilized?
Deep Brain Stimulator placement – Parkinson’s
Epilepsy focus ablation
Brain biopsy
What are the anesthetic considerations for stereotactic surgery?
- 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
What are the indications for an awake craniotomy?
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
