functional neurosurgery and anesthetic considerations susan m ryan, phd, md associate clinical...

Functional Neurosurgery and

Anesthetic Considerations

Susan M Ryan, PhD, MD

Associate Clinical Professor

Department of Anesthesia, UCSF

2006

What is Functional Neurosurgery?

“Neurosurgery intended to improve

or restore function by altering underlying

physiology”

Areas of Functional Neurosurgery

• Movement disorders

• Seizures

• Pain syndromes

• Psychiatric disorders

• Peripheral nerve injuries

Areas of Expansion

• Movement disorders

• Seizures

• Psychiatric disorders

Neurosurgical Techniques

• Deep brain stimulation (DBS)

• Selective ablationelectrodes

• Implantationviral vectors

stem cells

• Cranial nerve/ peripheral electrical stimulation

Functional Neurosurgery

• Began in mid-1900’s

• Eclipsed by effective medications

• Now: Non-responders Advanced cases

Neurosurgical Techniques

• Deep brain stimulationBest established use:

Parkinson’s Disease

• Vagal nerve stimulationBest established use:

Seizure disorders

DBS/VNS Studies in Progress

• Obesity

• Fibromyalgia

• Cluster headache

• Tourette’s Syndrome

• Depression

• Obsessive Compulsive Disorder

DBS for Parkinson’s Disease

Clinical Features

• ‘Pill-rolling’ tremor

• Masked faces

• ‘Cog-wheel’ rigidity

• Festinating gate

• Bradykinesia

Pathologic Features

• Progressive neuronal death

• Dopamine neurons of substantia nigra

• Non- dopamine populations in CNS and PNS• Bulbar function• Sympathetic chain• Parasympathetics of the gut

Basal Ganglia in PD

Treatment

• Medications• L-dopa + periph. inhibitor (Sinamet)

• Dopamine agonists

• MAO inhibitors

• COMT inhibitors

• Amantadine

DBS Surgery

• Goal: Improvement in PD symptoms

• Tremor• Rigidity• Hypokinesia• Gait• Balance

DBS Surgery

• Placement of stereotactic frame prior to procedure

• MRI to confirm coordinates

DBS Surgery

• Stereotactic head frame attached to bed

• Pt placed in sitting position

DBS Stereotactic Surgery

• Drill hole in skull to allow electrode placement for recording & stimulation

DBS Stereotactic Surgery

• Electrode passed slowly to record single cells in nucleus of interest

DBS Stereotactic Surgery

• Visual and auditory feedback of cell location and characteristics

DBS Stereotactic Surgery

• Listening for cell response during leg movement

DBS Surgery

• Find best location within the nucleus• Place stimulating electrode• Close burr hole, remove frame• Induce general anesthesia

• Tunnel leads• Place generator in upper chest wall

• Wait to activate stimulator in outpatient setting

Anesthesia: DBS Generator placement

• General anesthesia for generator placement

• No particular anestheticPropofol or inhaled agent work wellAvoid dopamine antagonistsAvoid demerol Muscle relaxants OK

• Prevent or treat emergence hypertension

• Not much pain in post-op setting

PD: Specific Issues

• Risk of exacerbation

Consider intraoperative continuation of medications

• Hemodynamics may be labile

Degeneration of sympathetic gangliaDopamine-related hypotension, hypovolemia

PD: Specific Issues

• Airway or pulmonary compromise

• Upper airway obstruction

• Dysarthria and history of choking

• Restrictive ventilatory pattern

• Aspiration risk

Patients with Existing DBS

• DBS is usually on 24/7 for PD pts

• May be off at night in other conditions

• Consider turning off prior to surgery

DBS: Surgical Risks

• Intracerebral hemorrhage

• Venous air embolism

• Emotional lability

DBS: Surgical Risks

Intracerebral hemorrhageIntracerebral hemorrhage

• Monitor patient for neurologic changes• Risk: 1.6% per lead

• Avoid hypertensionKeep SBP < 140Consider arterial line Antihypertensives: labetalol, hydralazine

DBS: Surgical Risks

Venous air embolismVenous air embolism• Early detection

• Communicate with surgeon

• Support blood pressure

• Provide O2

• Airway plan

DBS: Surgical Risks

Emotional LabilityEmotional Lability

• Usually no treatment needed• Consider sedation PRN

DBS Outcomes

Bilateral DBS of STN:

• N = 49

• Assessed at 1,3, and 5 years

• Assessed on and off meds and stimulation

(Krack, et al, NEJM 349, 2003)

DBS Outcomes

• Stimulation alone: significant improvement

• Synergy between meds and stimulation

• Allows decrease in medication doses

• Improvement in L-dopa dyskinesias

• Akinesia, speech, and freezing of gait all worsened

(Krack, et al, NEJM 349, 2003)

DBS vs Medical Therapy

• Randomized-pair trial:• DBS + optimized medical tx• Optimized medical tx

• 75% of pairs favored DBS + meds Quality of lifeSeverity of motor sxs off medication

(Deuschl et al, NEJM, 355, 2006)

DBS: other motor diseases

• Essential tremor

• Dystonia• More sedation during MRI

DBS and Tourette’s

• Motor/speech tics

• Up to 1% school age children

• 1/3 persist into adulthood

DBS for Tourette’s(Visser-Vandewalle, J. Neurosurg 99: 2003)

05

1015202530354045

# Tics Per Minute

#1 #2 #3

Pre DBS1 wk PostLong-term

DBS and Psychiatric Disease

• Depression• Pilot in 2005

• 4/6 patients improved >50% on testing

• Currently at least 3 ongoing NIH trials

• 10 to 20 patients per study

Vagus Nerve Stimulation

Vagus: Mixed Sensory and Motor

• 20% efferent: parasympathetic control of the heart and gut viscera

• 80% afferent: extensive connections to limbic and higher cortical systems

• Animal studies VNS: EEG changes and seizure cessation

Vagal Nerve Stimulation

• Approved device made by Cyberonics

• Chronic, intermittent stimulation to cervical vagus

• Prevents and aborts seizures

Vagal Nerve Stimulation

• Typical settings:

• Automatic: 30 sec stimulation q 5 min

• Additional manual: if pt feels aura, may wave wand over generator to activate stimulator

Vagal Nerve Stimulation

• Results from 3 studies:• Significant decrease in seizures: 24%-35%

• Controls: low-level stimulation

• Seizure frequency decreased further over time

• Decreased medication doses

VNS Surgery

• Performed under general anesthesia

• Leads wrapped around L vagus in neck

• Only L, and only unilateral

• Generator placed upper left chest

Final Electrode/tether Placement

Negative Electrode

Positive Electrode

Anchor Tether

VNS Surgery

• Possible intraop complications with lead testing:

• Arrhythmias- transient sinus arrest

• Labile hemodynamics

• Airway obstruction (vocal cord stimulation)- if not intubated

VNS Surgery

• Surgical complications:

• Infection: 2.9%

• Hoarseness or temporary vocal cord paralysis: 0.7%

• Hypesthesia or lower left facial paralysis: 0.7%

VNS Surgery: Chronic Side Effects

• Hoarseness

• Cough

• Paresthesias

• Dyspepsia

• Disrupted sleep

• Worsening sleep apnea

VNS: Anesthesia

• Pre-op considerations:

• Take usual seizure medications

• CBC, electrolytes

• EKG

• cardiac medications?

VNS: Anesthesia

• May use local, MAC, or GA

• Usually GA- no restriction on agents

• Endotracheal tube

• Blood loss is minimal

VNS: Anesthesia

• Anti-seizure medications induce hepatic enzymes-- higher anesthetic doses?

• Post-op seizures are common- be prepared

• Incidence of transient vocal cord paralysis

Chronic VNS

• Turn off for other surgery

• Restart in recovery

VNS for Depression

• Seizure pts with VNS: happier over time!

• N = 60 pts • previously failed numerous treatments

• 2 weeks on meds only

• 2 weeks stim adjust + meds

• 8 weeks fixed stimu + meds

VNS for Depression

• Open label study:• 30.5% of patients responded with significant

decrease in depression rating scale

• 15% full remission

• Substantial functional improvement, even in non-responders

VNS for Depression

• Placebo controlled study:• N= 225

• VNS-responding patients: 15%

• Placebo-responding patients: 10%

• Lower levels of stimulation

• Much to figure out, although now FDA approved

Other ongoing VNS studies

• Cervical VNS:• PTSD

• Panic disorder

• OCD

• Rapid-cycling bipolar disorder

• Bilateral diaphragmatic VNS• Morbid obesity

Functional Neurosurgery

• DBS• Targets stimulation

based on neuroanatomy. Tailors stim to the disorder.

• Invasive.

• Requires neurosurgery

• VNS• Simultaneous stimulation

of multiple tracts & nuclei.

• No specific target. Same stimulation for a number of disorders.

• Much less invasive. Does not require neurosurgeon.

• Procedure in search of an application?