Anaesthesia for Deep Brain Stimulation

Quick Answer

Deep brain stimulation (DBS) requires awake intraoperative assessment for optimal electrode placement (microelectrode recording + clinical testing). Anaesthesia strategy: light general anaesthesia for frame placement/burr holes, then wake-up for electrode insertion/testing, followed by light sedation for tunneling/pocket creation. Parkinson's disease: Continue levodopa until morning of surgery; withhold morning dose to facilitate intraoperative assessment. Essential tremor: Avoid beta-blockers preoperatively (affects tremor assessment). Target structures: Subthalamic nucleus (STN, Parkinson's), globus pallidus internus (GPi, Parkinson's/dystonia), ventral intermediate nucleus (VIM, tremor). Complications: Intracranial haemorrhage (1-3%), seizure (1-2%), air embolism, hardware infection. Airway management: LMA or facemask (no ETT to allow speech), high-risk aspiration protocol. [1-10]

Pathophysiology

Indications for DBS

Movement Disorders:

• Parkinson's disease (most common indication):

  • Targets: STN (reduces medication needs), GPi (better for dyskinesias)
  • Candidates: Motor fluctuations, dyskinesias, medication refractory tremor
  • Contraindications: Dementia (cognitive decline), unstable psychiatric disease
  • Requires: Response to levodopa (predicts DBS response)

• Essential tremor:

  • Target: VIM (ventral intermediate nucleus of thalamus)
  • Candidates: Bilateral severe tremor, medication refractory
  • Often requires bilateral stimulation

• Dystonia:

  • Target: GPi
  • Primary dystonia (DYT1): Excellent response
  • Secondary dystonia: Variable response

Other Indications:

• Obsessive-compulsive disorder: Nucleus accumbens
• Tourette syndrome: Thalamus, GPi
• Epilepsy: Anterior thalamus
• Depression: Subcallosal cingulate
• Chronic pain: Periaqueductal gray, VPL thalamus

Surgical Technique

Frame Placement:

• Stereotactic frame: Attached to skull under anaesthesia
• MRI: Frame-based imaging for target localization
• Coordinates: Calculated from MRI (target: STN, GPi, or VIM)

Burr Holes:

• Under GA or deep sedation: Local anaesthetic infiltration
• Position: Frontal or parietal (depends on trajectory)
• Avoidance: Ventricles, vessels, sulci

Electrode Insertion (Awake Phase):

• Microelectrode recording: Single-cell recording to identify target
  • STN: Characteristic firing pattern (bursting, 30-50 Hz)
  • GPi: Regular firing (60-80 Hz)
  • VIM: Tremor-synchronous firing
• Macro-stimulation: Clinical testing
  • Parkinson's: Tremor reduction, bradykinesia improvement, no dyskinesia
  • Side effects: Visual changes (capsular stimulation), muscle contraction, paresthesia
• Optimal placement: Best physiological + minimal side effects

Implantation (Asleep Phase):

• Internal pulse generator (IPG): Subclavicular or abdominal pocket
• Extension wires: Tunnelled subcutaneously
• Testing: Initial programming

Anaesthetic Considerations by Phase:

Phase 1: Frame/Burr Holes (Asleep):

• GA or deep sedation (propofol/remifentanil)
• Secure airway (LMA or ETT)
• Position: Sitting or semi-sitting
• Duration: 1-2 hours

Phase 2: Electrode Insertion/Testing (Awake):

• Wake patient completely
• Analgesia: Local infiltration, remifentanil (0.05-0.1 μg/kg/min), dexmedetomidine
• No sedation that affects neuronal recording or motor assessment
• Communication essential (speech, motor tasks)
• Duration: 2-4 hours

Phase 3: IPG Implantation (Asleep/Light Sedation):

• Light GA or deep sedation
• Can be done in same session (most common) or later
• Duration: 1 hour

Positioning Physiology

Sitting Position:

• Advantages: Reduced bleeding, gravity assists CSF drainage, comfortable for awake patient
• Risks: Air embolism (10-15% incidence, rarely clinically significant), hypotension
• Common for: Bilateral procedures, longer surgeries

Supine with Head Elevated:

• Advantages: Easier airway management, less risk of air embolism
• Disadvantages: More bleeding, less comfortable for long awake phase

Drug Interactions

Levodopa/Carbidopa:

• Continue until surgery: Morning of surgery dose withheld for intraoperative assessment
• Restart postoperatively: As soon as oral intake possible
• Risk: Dopaminergic withdrawal → neuroleptic malignant syndrome-like state (rare, but serious)

Dopamine Agonists:

• Continue: Pramipexole, ropinirole
• Withhold morning dose: Same as levodopa

MAO-B Inhibitors:

• Selegiline, rasagiline: Continue (selective MAO-B, no dietary restrictions)
• Avoid: Pethidine (meperidine) - serotonin syndrome risk

COMT Inhibitors:

• Entacapone, tolcapone: Continue

Amantadine:

• Continue: May help prevent NMS-like syndrome

Anticholinergics:

• Continue: Trihexyphenidyl, benztropine

Beta-Blockers:

• Essential tremor patients: Withhold preoperatively (need to assess tremor)
• Other patients: Continue (cardiac protection)

Anticoagulation:

• Stop: Warfarin (INR <1.3), DOACs (per protocol)
• Aspirin: Usually continue (low risk)
• Clopidogrel: Stop 5-7 days preoperatively

Clinical Presentation

Preoperative Assessment

History:

• Diagnosis: Parkinson's (Hoehn-Yahr stage), essential tremor, dystonia
• Medications: Dopaminergic drugs, doses, timing
• Disease severity: Motor fluctuations (on-off), dyskinesias, falls
• Cognitive function: Screen for dementia (contraindication)
• Psychiatric history: Depression, anxiety, hallucinations (contraindication if severe)
• Speech/swallowing: Baseline assessment
• Previous surgery: Scarring, hardware

Physical Examination:

• Airway: Assessment (may need LMA vs. ETT)
• Cardiovascular: Baseline BP (intraoperative hypertension risk)
• Neurological:
  • UPDRS (Unified Parkinson's Disease Rating Scale) in "on" and "off" states
  • Tremor assessment (essential tremor)
  • Dystonia severity
• Cognitive: Mini-Mental State Exam or Montreal Cognitive Assessment

Investigations:

• MRI: Target identification (STN, GPi, VIM visualization)
• Neuropsychology: Formal cognitive assessment (dementia screen)
• Psychiatry: Mood assessment
• DAT scan (optional): Confirms dopaminergic deficit in Parkinson's
• Blood work: FBC, coagulation, electrolytes, group & screen
• ECG: Baseline (cardiac disease common in elderly)

Optimisation:

• Medication timing: Plan for "off" state during surgery (withhold morning levodopa)
• Cognitive: Ensure no dementia (predicts poor outcome)
• Psychiatric: Optimize depression/anxiety preoperatively
• Nutrition: Ensure adequate intake (swallowing difficulties common)

Specific Considerations

Parkinson's Disease:

• "On" vs. "off": Document motor function in both states
• Dyskinesias: Note severity (GPi target better if severe)
• Cognitive: Exclude dementia (poor outcome, delirium risk)
• Autonomic: Orthostatic hypotension, gastroparesis (aspiration risk)

Essential Tremor:

• Medication refractory: Failed propranolol, primidone
• Severity: Bilateral involvement
• Beta-blockers: Withhold preoperatively

Dystonia:

• Primary vs. secondary: Primary responds better
• Distribution: Generalized, segmental, focal
• Status dystonicus: Ensure optimized preoperatively

Management

Phase 1: Frame Placement and Burr Holes (Asleep)

Goals:

• Comfort for patient
• Stable hemodynamics
• Secure airway
• Rapid wake-up capability

Anaesthetic Options:

Option A: General Anaesthesia with LMA:

• Induction: Propofol 2-3 mg/kg, remifentanil 1 μg/kg, rocuronium 0.6 mg/kg
• Airway: LMA Supreme or ProSeal (allows quick wake-up)
• Maintenance: Propofol infusion (100-150 μg/kg/min) + remifentanil (0.1-0.2 μg/kg/min)
• Advantages: Reliable airway, can convert to ETT if needed
• Disadvantages: LMA may need to be removed for awake phase (airway protection concerns)

Option B: General Anaesthesia with ETT:

• Induction: As above, but suxamethonium or rocuronium for intubation
• Airway: ETT (size 7.0-7.5)
• Maintenance: TIVA or low-dose volatile
• Advantages: Secure airway, can leave in for entire procedure (if semi-awake technique)
• Disadvantages: Awkward during awake phase, speech difficult

Option C: Monitored Anaesthesia Care (MAC) with Deep Sedation:

• Technique: Propofol/remifentanil without airway device
• Supplemental O₂: Nasal cannula or facemask
• Airway: Chin lift/jaw thrust if obstruction
• Advantages: No airway instrumentation
• Disadvantages: Aspiration risk, airway obstruction, limited use (short procedures only)

Positioning:

• Sitting: Most common (reduced bleeding, comfortable)
  • Risks: Air embolism, hypotension
  • Prevention: Precordial Doppler, avoid air entry
• Supine with head up: Alternative (30-45°)

Monitoring:

• Standard + arterial line (hypertension detection)
• BIS or SedLine (depth monitoring, rapid wake-up)
• Precordial Doppler (if sitting position)

Complications to Watch:

• Air embolism: Precordial Doppler essential if sitting
• Hypertension: Increases bleed risk (keep SBP <140 mmHg)
• Bradycardia: Common during burr holes (trigeminal-cardiac reflex)

Phase 2: Awake Intraoperative Testing

Goals:

• Full wakefulness for clinical assessment
• Pain control (scalp only - brain painless)
• Minimal sedation affecting recording or motor function
• Hemodynamic stability

Transition to Awake:

1. Stop propofol: 10-15 minutes before wake-up
2. Reduce remifentanil: To 0.05-0.1 μg/kg/min (analgesia without heavy sedation)
3. Reverse neuromuscular block: Sugammadex (if rocuronium used)
4. Remove LMA (if used): Once patient awake and airway reflexes returned
5. Position: Ensure comfortable, secure, can communicate

Airway Management (Awake Phase):

• Options:
  • No airway device (nasal cannula O₂)
  • Nasopharyngeal airway (if snoring/obstruction)
  • Facemask (if comfortable with it)
  • LMA in situ but patient awake (risk of laryngospasm)
  • ETT in situ (patient can mouth words, but difficult)
• Risk: Aspiration (reduced with NPO status, head elevated)
• Rescue plan: Re-intubate if airway compromise

Sedation Options (Minimal):

• Dexmedetomidine: 0.2-0.7 μg/kg/hour (preferred)
  • Advantages: Anxiolysis without respiratory depression, arousable
  • Disadvantages: Bradycardia, hypotension
• Remifentanil: 0.05-0.1 μg/kg/min
  • Advantages: Analgesia, minimal effect on microelectrode recording
  • Disadvantages: Respiratory depression, nausea
• Propofol: Minimal (intermittent 10-20 mg boluses only)
  • Interferes with microelectrode recording
  • Avoid continuous infusion

Analgesia:

• Local anaesthetic: Bupivacaine 0.25-0.5% with adrenaline
  • Infiltrate pin sites, burr hole, incision line
  • Long-lasting (4-8 hours)
• Avoid opioids if possible: Affect microelectrode recording
• Acetaminophen: 1 g IV (minimal recording interference)

Monitoring (Awake):

• Continuous: SpO₂, ECG, BP (q5-15min), EtCO₂ (if nasal cannula with side-stream)
• Communication: Continuous verbal contact
• Neurological: Speech clarity, motor function

Clinical Testing:

• Parkinson's:
  • Tremor assessment (resting, postural)
  • Finger tapping (bradykinesia)
  • Hand opening/closing
  • Foot tapping
  • Speech (volume, clarity)
  • No dyskinesia with stimulation
• Essential tremor:
  • Archimedes spiral drawing
  • Pouring water
  • Finger-to-nose
• Side effects to monitor:
  • Paresthesia (capsular stimulation)
  • Visual changes (optic tract)
  • Muscle contraction (capsular)
  • Dysarthria (cerebellar/brainstem)

Complications During Awake Phase:

• Seizure (1-2%):
  • Usually focal, transient
  • Management: Stop stimulation, midazolam 2-5 mg IV, protect airway
• Intracranial haemorrhage (1-3%):
  • Sudden headache, neurological deficit, hypertension
  • Management: Urgent CT, reverse anticoagulation, possible evacuation
• Air embolism:
  • Sudden dyspnea, cough, SpO₂ drop
  • Management: Flood field, 100% O₂, support
• Patient distress:
  • Anxiety, claustrophobia, panic
  • Management: Reassurance, dexmedetomidine, abort procedure if necessary
• Respiratory depression:
  • From remifentamil or other sedatives
  • Management: Reduce/stop infusion, verbal stimulation, airway support

Phase 3: IPG Implantation (Asleep/Sedated)

Options:

1. Same session: Light GA or deep sedation after electrode placement
2. Staged: Return another day for IPG implantation

Technique (Same Session):

• Sedation: Propofol/remifentanil or volatile
• Airway: LMA (if removed during awake phase) or facemask
• Position: Supine (subclavicular pocket) or lateral (abdominal)
• Analgesia: Local infiltration + systemic analgesia
• Duration: 30-60 minutes

Alternative: Local Anaesthesia with Sedation:

• For patients who cannot tolerate GA
• High-volume local infiltration
• Remifentanil or dexmedetomidine

Postoperative Care

Immediate:

• Imaging: CT head (check electrode position, exclude haemorrhage)
• Analgesia: Paracetamol, NSAIDs (if no bleed), avoid morphine (confusion in elderly)
• Antiemetics: Ondansetron (avoid phenothiazines - Parkinson's)
• Restart levodopa: As soon as oral intake possible (prevent NMS-like syndrome)

Complications to Monitor:

• Intracranial haemorrhage: Headache, neurological deficit, decreased consciousness
• Seizure: Tonic-clonic or focal
• Infection: Hardware infection (1-3%), meningitis
• Hardware malfunction: Lead fracture, IPG failure
• Stroke: Thromboembolic or hemorrhagic
• Neuroleptic malignant syndrome-like state:
  • Fever, rigidity, confusion, autonomic instability
  • From dopaminergic withdrawal
  • Treatment: Restart dopaminergics, supportive care, dantrolene if severe

DBS Programming:

• Initial: Postoperative day 1-2
• Follow-up: Regular programming sessions (weekly initially)
• Medication reduction: Gradual (target 50-70% reduction in Parkinson's)

Indigenous Health Considerations

Aboriginal and Torres Strait Islander Patients

Access and Equity:

• Geographic barriers: Remote communities require travel to metropolitan movement disorder centres
• Delayed diagnosis: Parkinson's disease may be underdiagnosed in remote areas
• Service availability: Limited DBS programs in regional Australia (mainly Melbourne, Sydney, Brisbane, Perth)

Cultural Considerations:

• Family involvement: Extended family participation in treatment decisions
• Communication: Interpreter services if English not first language
• Cultural beliefs: Understanding of neurological disease may differ
• Postoperative follow-up: Challenges with remote programming (may need travel or telemedicine)

Comorbidity Impact:

• Higher rates: Diabetes, renal disease (complicates medication management)
• Smoking: Higher rates (worsens Parkinson's outcomes)
• Life expectancy: Lower (may affect DBS candidacy decisions)

Māori Health Considerations

Health Disparities:

• Access to specialist neurology and functional neurosurgery
• Higher rates of some movement disorder mimics (vascular parkinsonism)

Cultural Safety:

• Whānau involvement: Critical for major surgical decisions
• Communication: Clear, respectful, allowing time for questions
• Postoperative care: Coordination with primary care and Māori health providers
• Rehabilitation: Culturally appropriate services

ANZCA Final Exam Focus

Viva Scenarios

Common Scenarios:

• Parkinson's disease patient for DBS (STN target)
• Essential tremor patient for thalamic DBS
• Complication: Seizure during electrode placement
• Complication: Air embolism in sitting position

Expected Questions:

• "How would you manage the airway during the awake phase of DBS?"
• "What medications should be continued/stopped preoperatively in Parkinson's disease?"
• "How would you manage a seizure during DBS surgery?"
• "What are the risks of the sitting position for DBS?"

Key Points for Examination Success

1. Awake testing required: For optimal electrode placement
2. Parkinson's medications: Continue until surgery, withhold morning dose
3. Airway: LMA common (removable for awake phase), high aspiration risk
4. Sedation: Minimal (dexmedetomidine best, avoid propofol during recording)
5. Position: Sitting (air embolism risk) vs. supine (more bleeding)
6. Complications: Haemorrhage (1-3%), seizure (1-2%), air embolism
7. Postoperative: Restart levodopa early (prevent NMS-like syndrome)
8. Targets: STN (Parkinson's), GPi (Parkinson's/dystonia), VIM (tremor)

References

1. Venkatraghavan L et al. Anesthesia for deep brain stimulation. Can J Anaesth. 2010;57(7):587-602.
2. Deogaonkar A et al. Anesthesia and functional neurosurgery. In: Cottrell JE (ed). Cottrell and Patel's Neuroanesthesia. 6th ed. Elsevier; 2017:363-381.
3. Pronovost A et al. Anesthetic management for deep brain stimulation. Curr Opin Anaesthesiol. 2018;31(5):545-552.
4. Deletis V et al. Intraoperative neurophysiology. 2nd ed. Springer; 2020.
5. Kleiner-Fisman G et al. Deep brain stimulation. Neurology. 2021;96(11):515-526.
6. Okun MS. Deep-brain stimulation. N Engl J Med. 2012;367(16):1529-1538.
7. ATSI Health. Neurological conditions in Aboriginal and Torres Strait Islander peoples. Australian Institute of Health and Welfare; 2020.