1) Functional neurosurgery involves altering the activity of normal nervous system areas to improve function, using ablation, stimulation, or drugs. Stereotaxis allows precise tissue targeting. 2) Early localization involved ventricle cannulation, while CT and MRI now directly image structures and provide 3D data for stereotactic guidance. Instruments include base rings, aiming arcs, and guide blocks. 3) Procedures include DBS for movement disorders like Parkinson's and essential tremor, as well as chronic pain, psychiatric issues, and seizures. DBS suppresses overactivity at high frequencies. Anaesthetic considerations depend on the patient and procedure.

1. Anaesthesia for
Functional
Neurosurgery
Presented by – Dr. Dhritiman
Moderated by – Dr. Radhakrishnan M

2. Definitions
• Functional neurosurgery is altering the activity of an grossly
normal area of the nervous system either ablatively,
electrically, or pharmacologically in order to establish more
normal overall patient function.
• Stereotaxis is a means of non invasive precise localization of
the target tissue.

3. History
Prior to the introduction of CT and MRI, target localization
most frequently involved cannulating the lateral ventricle
through a burr- hole and injecting air or a positive contrast
substance in order to outline third ventricular structures
adjacent to diencephalic targets.

4. CT and MRI based Stereotactic
Localization
• CT and MRI have the advantage of directly imaging CNS
structures, and both techniques provide a 3-dimensional data
base which can then be translated into Stereotactic space.
• One method uses lateral scout film for Z-coordinate
localization and Axial cuts for X and Y axis localization.
Z
Y
X

5. Instruments
• General parts (of arc centering arc radius type):
1. Base ring
2. Aiming arc.
3. Guide block.
4. Vertical bars.

6. Functional Stereotactic Procedures
• Movement disorders (Ablative or DBS)
1. Parkinson disease
2. Essential tremor
3. Dystonia
4. Myoclonus
5. Others (chorea, torticollis, spasticity)
• Chronic pain (Trigeminal Neuralgia, Cluster Headaches, Cancer Pain,
Chronic pain syndromes)
• Psychiatric disorders (bilateral anterior capsulotomy)
1. Chronic depression
2. Obsessive compulsive
• Seizure disorders (Ablative – MTL, Amygdalo-hippocampectomy,
Epileptic foci, corpus callosotomy)
• Multiple sclerosis

7. DBS for Parkinson’s Disease
•Ventral intermediate
thalamus discharge
suppression associated with
tremor relief;
•Pallidal lesioning associated
with bradykinesia relief.
•Now Sub-thalamic nuclei
have been seen as a putative
therapeutic target for
Parkinson’s disease.

8. DBS for Parkinson’s Disease
• The reversible non destructive nature of DBS makes it attractive.
• DBS works only in dopamine responsive patients and gives more
“on” time before switch off effect. Improvement generally is equal
to or less than the patient’s best drug response.
• The DBS devices are set at a high suppressive frequency (typically
130–180 Hz) with the aim of suppressing overactivity in the
pallidum or STN in Parkinson’s disease, or overactivity in the
thalamus for tremor, or in Pallidal motor processing in dystonia.

9. Parkinson’s Disease and Anaesthesia

10. Surgical procedure of DBS
• Two components to the surgical procedure,
1) Implantation of the electrodes in the brain, and
2) Running connections subcutaneously to the implantable pulse
generator (IPG)
Define target with stereotactic frame  Use frame to place
electrodes in target  Confirm electrode placement using
neurophysiological recordings or on table stimulation or CT
imaging  Connecting the electrodes to the extension lead
which are tunnelled under the skin and connected to the IPG or
Trial with EPG and implanting in a 2 stage procedure.

11. Anaesthetic Implications
• Factors governing anaesthesia choice:
1) the patient’s presenting condition (age/comorbidities),
2) the degree of central movement abnormality (dystonia C/I for
LA), and
3) the ability of the patient to tolerate the procedure under local
anaesthesia.
4) Bleeding disorders and Refractory hypertension are C/I to
stereotactic surgery.
5) Paediatric patients - GA
Placement of frame – LA with or without Sedation.
CT/MRI scan for localization – No anaesthesia or Sedation
Electrode placement – Sedation (Opioids/Dexmed) or GA
Tunneling and connection to IPG – GA

12. Placement of Frame
• Usually done outside OT in either sitting or supine position.
• Local infiltration of pin sites or scalp block with or without
sedation may be used.
• Prior explanation of sensation of ‘ring like’ tightness in scalp
to prevent anxiety.
• Children electively intubated prior to frame placement.
• Frame with intubation hoop preferred.

13. Transport to Radiology Dept. for
Imaging
• Transport monitoring necessary.
• Wrench for removing head ring should be present.
• Placing a thin sand bag or rolled towel under shoulders helps
to extend the head as frame limits its extension.
• Careful management of sedative medication, if any.
• While contrast scanning, be alert for contrast reaction.

14. In OT for Stereotactic procedure
• Before procedure, scanning images are loaded on a PC and
coordinates calculated – takes some time.
• Patients head gets fully draped for procedure, so limited
access. Use of right angle bar on OT table gives some access.
• Nasopharyngeal airway may be inserted preemptively. A
portex ETT connector may be fitted on the airway for O2
supplementation and EtCO2 cable connected easily for
monitoring.

15. • Always be aware of the possibility of convulsions with the frame in
situ. For longer duration procedures, anticonvulsant medication should
be given as per dosage schedule.
• If conversion to GA is required intraop, mask ventilation with frame is
difficult. Also in spite of intubation hoop, positioning for intubation is
difficult due to frame and laryngoscopy view may increase by 1 CL
grade. OELM and smaller size ETT placement may be used for ease of
intubation.
• Mayfield clamp is usually used to fix patients head. While lateral
positioning, be wary of base ring encroaching on patients neck and
shoulder, especially in obese patients.

16. • Fluid management in awake patients with no catheterization
is a problem. Restrictive intraop fluid administration and use
condom drainage.
• Use of a semi-sitting or sitting position may increase the risk
of venous air embolism in spontaneously breathing patients
and thus EtCO2 monitoring is must. Doppler monitoring is an
option.
• Comfortable positioning of patient with padding is important.
• Intraop hypertension needs to be avoided due to danger of
bleeding (studies show increased risk). Dexmedetomidine has
been found to be useful in this regard.
• Continuation of L-dopa according to dosage schedule
perioperatively.

17. Complications and Adverse effects
1. Intraop Bleeding.
2. Intraop Seizures (focal more common than GTCS).
3. Venous Air Embolism
4. Postop neurological deficits.
5. CSF leak.
6. Device migrating, fracturing, or becoming infected.
• Late Adverse effects:
1. Mood disturbance (d/t STN stimulation or reduction in
doses of L-dopa)
2. Weight Gain.
3. Future limitations for MRI imaging.

18. Patients with DBS in situ
• MRI can cause effects like heating, physical movement of
stimulator, unintended stimulation, program changes in
stimulator.
• Electrocautery modifications:
1) Bipolar, whenever possible.
2) Unipolar with low voltage, low power, ground plate far from
device.
• Defibrillation modifications:
1) Position paddles far away.
2) Use lowest clinically appropriate energy output.

19. Trigeminal Neuralgia
• Severe unilateral paroxysmal facial pain with patient specific triggers and
pain zones.
• Associated with aberrant arterial loop compressing on Trigeminal nerve at
REZ.
• Initial treatment is medical – Carbamazepine .
• Surgical treatment options include:
1) Percutaneous Trigeminal Rhizotomy.
2) MVD

20. Percutaneous Trigeminal Rhizotomy
• Lesioning trigeminal rootlets either with glycerol or radiofrequency (RF)
current.
• Low complication rate; slow onset temporary pain relief with glycerol;
rapid onset temporary pain relief with RF.
• Surgical technique consists of entering 2 cm lateral to angle of mouth and
aiming for mid point of foramen ovale and injecting/lesioning in the CSF
space around gasserian ganglion.
• Anaesthesia, if any consists of:
1) Local anaesthetic infiltration at needle entry site.
2) Low dose background infusion of sedative/analgesic (easily arousable)
3) Temporary deepening of anaesthesia when foramen ovale is punctured
(thiopentone/methohexital).
4) Temporary deepening if required when actual RF lesioning is taking place
(not preferable).

21. Microvascular Decompression
• Longer lasting complete pain relief; higher complication rate.
• 10% complication rate - ipsilateral hearing loss, temporary vertigo, ataxia,
trochlear or facial nerve palsy, or CSF fistula.
• Age group 18 - >70 yrs. Anaesthetic technique to suit age group and
comorbidities.
• Semi-sitting or Lateral decubitus position.
• Special monitoring – BAER (frequent traction on 8th nv), Facial Nerve
monitoring.

22. Vagal Nerve Stimulation
• FDA approval of VNS for:
1. Adjunctive therapy for partial-onset epilepsy (1997)
2. Refractory depression (2005)
• Adverse effects:
1) Coughing, dyspnea, voice changes on initial stimulation.
2) Worsening of Sleep apnea
3) Cardiac Arrythmia
4) Involuntary arm movement, torticollis.
• The left vagus nerve is stimulated rather than the right because the right
plays a role in cardiac function such that stimulating it could have negative
cardiac effects.

23. Direct VNS Transcutaneous VNS

24. Carotid Sinus Stimulation
Rheos, CVRx Inc, Minneapolis, Minn

25. 1) Carotid baroreceptor stimulation is effective in reducing blood
pressure of conscious normotensive dogs and in obesity-induced
hypertension.
2) Blood pressure reduction is significantly attenuated, but not
abolished, in angiotensin II-induced hypertension.
3) Blood pressure reduction with the device is unaltered by renal
denervation, casting doubts on the role of renal innervation in
mediating the effects of the carotid baroreflex on blood pressure
regulation.
4) Blood pressure reduction is accompanied by a significant decrease in
plasma noradrenaline levels.
5) DebuT-HT Trial (JACC 2010) studied 45 patients with mean BP of
179/105 mm Hg and heart rate was 80 beats/min after implantation
of the said device and found mean blood pressure was reduced by
21/12 mm Hg after 3 months and of 33/22 mm Hg after 2 yrs follow
up.

26. Thank You