FRCA Notes

Awake Craniotomy

This topic appeared as a CRQ in 2021 (41% pass rate), with use of dexmedetomidine, drugs for terminating intra-operative seizures and specific intra-operative complications all coming under the microscope.

Resources

  • Probably more appropriately called 'craniotomy with intra-operative awakening'

Benefits of awake vs. asleep craniotomy
Less PONV
Less post-operative pain
Reduced length of stay
Reduced hospital costs
Improved patient satisfaction

Indications

  • Resection of brain tumours in or near eloquent areas
    • For most axial/intrinsic brain tumours surgical excision is not curative
    • By the time the tumour is symptomatic, cells are widely migrated, making complete excision impossible
    • E.g. low grade gliomas have no distinct boundaries with surrounding brain parenchyma
    • Therefore, the goals of surgery are to:
      • Reduce tumour bulk to a maximal extent with minimal functional consequences
      • Relieve symptoms
      • Optimise the efficacy of chemo/radiotherapy
  • Deep brain stimulation
  • Epilepsy surgery
  • Resection of intracranial vascular lesions supplying functionally important areas

  • Damage to functionally important areas e.g. of speech, motor control, cognitive cortices can be devastating, and tumours in this area are commonly performed under awake craniotomy
    • In order to reduce the risk of iatrogenic neurological deficit the surgeon establishes which areas of the brain in the vicinity of the tumour serve important functions
    • This is done via 'functional mapping', which helps balance completeness of tumour resection and functional preservation
    • There is too greater an inter-individual heterogeneity to use established maps of cytoarchitecture, such as Brodmann areas, for all patients

  • The gold standard technique for mapping is direct cortical electrical stimulation whilst awake
  • The patient performs a task relevant to that area to determine whether the stimulus disrupts execution of the task

  • Non-invasive mapping techniques include functional MRI (fMRI), diffusion tensor imaging (DTI) and repetitive transcranial magnetic stimulation (rTMS)
    • These can aid the process by providing information about possible eloquent regions
    • This helps inform surgical approach and intra-operative vigilance during resection
    • These non-invasive techniques are imperfect and cannot be wholly relied upon to inform resection as:
      • fMRI does not directly measure function
      • DTI maps white matter pathways assumed to be functional
      • Peri-neoplastic changes such as mass effect and oedema reduce the sensitivity of both fMRI and DTI techniques
      • rTMS can only map cortical areas; awake surgery allows mapping of sub-cortical areas too

  • MEP and SSEP monitoring can be performed in the anaesthetised patient and provide motor and sensory mapping information independent of patient cooperation/effort
    • Visual fields and some higher cognitive functions can also be mapped
    • However awake surgery remains indispensable for language mapping

Perioperative management of the patient undergoing awake craniotomy


  • Adequate patient preparation and selection is vital
  • Absolute contraindications include:
    • Refusal
    • Inability to remain still e.g. movement disorders
    • Inability to cooperate e.g. confused, cognitive impairment
    • Surgical requirement for prone positioning
  • Relative contraindications include other factors that will preclude staying still (e.g. chronic cough) or cooperation (language barriers, young age, learning difficulties)

  • Standard pre-operative care for neurosurgery applies
  • Patients should ensure they have taken anti-convulsants; some centres load patients with anti-convulsants or check plasma levels to ensure within therapeutic range

Monitoring and access

  • AAGBI
  • Wide-bore IV access (placed ipsilateral to lesion)
  • Arterial line (placed ipsilateral to lesion)
  • Catheters may cause discomfort in the awake phase; convenes with judicious use of fluids may be preferable
  • EEG/BIS monitoring may allow more accurate guiding of drug dosing and facilitate the quality and speed of intra-operative awakening

Pre-mapping phase (→ craniotomy and exposure of the brain)


Anaesthetic option Technique Notes
General anaesthesia
('asleep - awake - asleep') 		Propofol/remifentanil TCI
IPPV via LMA		 Facilitates rapid wake-up
Allows removal of LMA prior to coughing
Neuroleptanalgesia Droperidol + alfentanil
Conscious sedation Dexmedetomidine
Loading dose of 0.5 – 1.0 µg/kg over 10 min
Infusion rate of 0.2 – 1.0 µg/kg/hr 		Provides a rousable, sleep - like sedation
Provides analgesia
Maintained respiratory drive
Rapid pharmacokinetics
Higher risk of on-table seizures vs. propofol
Awake LA ± small doses opioid e.g. alfentanil, remifentanil E.g. elderly patient
  • Comfort and haemodynamic stability is required during more stimulating/painful aspects:
    • Skull pin placement
    • Craniotomy itself
    • Dural opening

  • Simple analgesics can be used e.g paracetamol
  • Local anaesthetic scalp block provides good, safe analgesia by blocking seven nerves:
    1. Supra-orbital
    2. Supra-trochlear
    3. Zygomatico-temporal
    4. Auriculo-temporal
    5. Greater auricular (C2/3)
    6. Greater occipital (C2)
    7. Lesser occipital (C2/3)

Awake, mapping phase (→ cortical & sub-cortical mapping, and excision of the lesion)

  • Must ensure patient is:
    • Awake
    • Comfortable
    • Cooperative
  • This facilitates acquisition of reliable neurophysiological monitoring signals

Post-mapping phase (→ haemostasis and wound closure)

  • This phase involves haemostasis, dural closure and skull & skin closure
  • These aspects are uncomfortable, superimposed on discomfort from:
    • Musculoskeletal discomfort from lying immobile for a long time
    • Scalp block wearing off

  • Options include:
    • General anaesthesia; patients are usually in the right lateral position with head clamped and so an LMA is often preferred
    • Sedation
    • Awake

  • Return to neurosurgical ward or HDU area
  • Close neurological monitoring for complications; post-operative haematoma is most likely in the first 6hrs after operating
  • Analgesia as for other craniotomy

  • Complications are overall rare
Complication Incidence
Intra-operative seizures 3 - 16%
Cardiovascular instability e.g. bradycardi 17 - 24%
Post-operative neurological dysfunction 17 - 23%
Airway obstruction/hypoventilation 7 - 16%
Cerebral oedema ('tight' brain) 7 - 14%
Conversion to GA 2%
PONV ≤10%

Seizures

  • Intra-operative seizures are most likely to occur during cortical mapping
  • Management is with:
    • Irrigating the brain with ice-cold saline
    • Benzodiazepines e.g. lorazepam 4mg IV
    • Anti-epileptic drugs e.g. levetiracetam 40mg/kg
    • Bolus of anaesthetic agent e.g. propofol, thiopentone
    • Re-sedation and airway control

Patient intolerance

  • Typically arises from discomfort from urinary catheters or prolonged positioning
  • Conversion to GA may be required, but the rate of this is low