Anaesthesia for Functional

Neurosurgery

Presented by – Dr. DhritimanModerated by – Dr. Radhakrishnan M

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.

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.

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

Instruments• General parts (of arc centering arc radius type): 1. Base ring2. Aiming arc.3. Guide block.4. Vertical bars.

Functional Stereotactic Procedures• Movement disorders (Ablative or DBS)1. Parkinson disease 2. Essential tremor 3. Dystonia 4. Myoclonus5. Others (chorea, torticollis, spasticity)• Chronic pain (Trigeminal Neuralgia, Cluster Headaches, Cancer Pain,

Chronic pain syndromes)• Psychiatric disorders (bilateral anterior capsulotomy)1. Chronic depression2. Obsessive compulsive• Seizure disorders (Ablative – MTL, Amygdalo-hippocampectomy,

Epileptic foci, corpus callosotomy)• Multiple sclerosis

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.

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.

Parkinson’s Disease and Anaesthesia

Surgical procedure of DBS• Two components to the surgical procedure,1) Implantation of the electrodes in the brain, and2) 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.

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 SedationElectrode placement – Sedation (Opioids/Dexmed) or GATunneling and connection to IPG – GA

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.

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.

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.

• 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.

• 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.

Complications and Adverse effects

1. Intraop Bleeding.2. Intraop Seizures (focal more common than GTCS).3. Venous Air Embolism4. 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.

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.

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

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).

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.

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 apnea3) Cardiac Arrythmia4) 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.

Direct VNS Transcutaneous VNS

Carotid Sinus Stimulation

Rheos, CVRx Inc, Minneapolis, Minn

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.

Thank You