Functional Neurosurgery and Anesthetic Considerations

1. Functional Neurosurgery and Anesthetic Considerations Susan M Ryan, PhD, MD Associate Clinical Professor Department of Anesthesia, UCSF 2006

2. What is Functional Neurosurgery? “Neurosurgery intended to improve or restore function by altering underlying physiology”

3. Areas of Functional Neurosurgery • Movement disorders • Seizures • Pain syndromes • Psychiatric disorders • Peripheral nerve injuries

4. Areas of Expansion • Movement disorders • Seizures • Psychiatric disorders

5. Neurosurgical Techniques • Deep brain stimulation (DBS) • Selective ablation electrodes • Implantation viral vectors stem cells • Cranial nerve/ peripheral electrical stimulation

6. Functional Neurosurgery • Began in mid-1900’s • Eclipsed by effective medications • Now: Non-responders Advanced cases

7. Neurosurgical Techniques • Deep brain stimulation Best established use: Parkinson’s Disease • Vagal nerve stimulation Best established use: Seizure disorders

8. DBS/VNS Studies in Progress • Obesity • Fibromyalgia • Cluster headache • Tourette’s Syndrome • Depression • Obsessive Compulsive Disorder

9. DBS for Parkinson’s Disease

10. Clinical Features • ‘Pill-rolling’ tremor • Masked faces • ‘Cog-wheel’ rigidity • Festinating gate • Bradykinesia

11. 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

12. Basal Ganglia in PD

14. Treatment • Medications • L-dopa + periph. inhibitor (Sinamet) • Dopamine agonists • MAO inhibitors • COMT inhibitors • Amantadine

15. DBS Surgery • Goal: Improvement in PD symptoms • Tremor • Rigidity • Hypokinesia • Gait • Balance

17. DBS Surgery • Placement of stereotactic frame prior to procedure • MRI to confirm coordinates

18. DBS Surgery • Stereotactic head frame attached to bed • Pt placed in sitting position

19. DBS Stereotactic Surgery • Drill hole in skull to allow electrode placement for recording & stimulation

20. DBS Stereotactic Surgery • Electrode passed slowly to record single cells in nucleus of interest

21. DBS Stereotactic Surgery • Visual and auditory feedback of cell location and characteristics

22. DBS Stereotactic Surgery • Listening for cell response during leg movement

23. 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

24. Anesthesia: DBS Generator placement • General anesthesia for generator placement • No particular anesthetic Propofol or inhaled agent work well Avoid dopamine antagonists Avoid demerol Muscle relaxants OK • Prevent or treat emergence hypertension • Not much pain in post-op setting

25. PD: Specific Issues • Risk of exacerbation Consider intraoperative continuation of medications • Hemodynamics may be labile Degeneration of sympathetic ganglia Dopamine-related hypotension, hypovolemia

26. PD: Specific Issues • Airway or pulmonary compromise • Upper airway obstruction • Dysarthria and history of choking • Restrictive ventilatory pattern • Aspiration risk

27. 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

28. DBS: Surgical Risks • Intracerebral hemorrhage • Venous air embolism • Emotional lability

29. DBS: Surgical Risks Intracerebral hemorrhage • Monitor patient for neurologic changes • Risk: 1.6% per lead • Avoid hypertension Keep SBP < 140 Consider arterial line Antihypertensives: labetalol, hydralazine

30. DBS: Surgical Risks Venous air embolism • Early detection • Communicate with surgeon • Support blood pressure • Provide O2 • Airway plan

31. DBS: Surgical Risks Emotional Lability • Usually no treatment needed • Consider sedation PRN

32. 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)

33. 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)

34. DBS vs Medical Therapy • Randomized-pair trial: • DBS + optimized medical tx • Optimized medical tx • 75% of pairs favored DBS + meds Quality of life Severity of motor sxs off medication (Deuschl et al, NEJM, 355, 2006)

35. DBS: other motor diseases • Essential tremor • Dystonia • More sedation during MRI

36. DBS and Tourette’s • Motor/speech tics • Up to 1% school age children • 1/3 persist into adulthood

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

38. 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

39. Vagus Nerve Stimulation

40. 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

41. Vagal Nerve Stimulation • Approved device made by Cyberonics • Chronic, intermittent stimulation to cervical vagus • Prevents and aborts seizures

43. 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

44. 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

45. VNS Surgery • Performed under general anesthesia • Leads wrapped around L vagus in neck • Only L, and only unilateral • Generator placed upper left chest

46. Final Electrode/tether Placement Anchor Tether Negative Electrode Positive Electrode

47. VNS Surgery • Possible intraop complications with lead testing: • Arrhythmias- transient sinus arrest • Labile hemodynamics • Airway obstruction (vocal cord stimulation)- if not intubated

48. VNS Surgery • Surgical complications: • Infection: 2.9% • Hoarseness or temporary vocal cord paralysis: 0.7% • Hypesthesia or lower left facial paralysis: 0.7%

49. VNS Surgery: Chronic Side Effects • Hoarseness • Cough • Paresthesias • Dyspepsia • Disrupted sleep • Worsening sleep apnea

50. VNS: Anesthesia • Pre-op considerations: • Take usual seizure medications • CBC, electrolytes • EKG • cardiac medications?