1. Anaesthetic considerations in posterior fossa surgery Dr. S. Parthasarathy MD., DA., DNB, MD (Acu), Dip. Diab. DCA, Dip. Software statistics PhD (physio) Mahatma Gandhi medical college and research institute, puducherry – India

4. Boundaries :  Anteriorly : clivus, petrous part of temporal bone  Posteriorly : occipital bone  Laterally : squamous and mastoid part of the temporal bone  Superiorly : tentorium cerebelli  Inferiorly : Foramen magnum

5. Why do we specially care about this ?? brainstem, The cerebellum fourth ventricle. What is in brainstem??

6. The Respiratory center; The Cardiovascular center; The Swallowing center; The Center of vomiting, coughing, and/or hiccups; The Chewing center; The Salivary centers. The Brainstem Reticular Substance

7. The cerebellum coordination, controlling voluntary and involuntary motor activity like balance and locomotion alcoholic ?? cranial nerve nuclei Flow of CSF

8. Tumours Young – primary tumours and aneurysms Medulloblastomas, ependymomas, glioma astrocytomas glomus jugulare tumors ( Pneumonic - MEGA – GA ) Old age -- ?? Secondary lesions

9. Presentation ICH - herniation, ischemia Movement disorders Cerebellum Autonomic disturbance Cranial nerve disorders

10. Preanaesthetic concerns Routine + + + + Cardiovascular status – is he/she fit for sitting position ?? Altered sensorium Cranial nerve palsies, aspiration pulmonary infection Debilitation and nutrition Diuretics and electrolytes

11. Preanaesthetic concerns Discussion with surgeon for invasive monitors Preoperative audiometry is useful in predicting hearing preservation after acoustic shwannoma surgery Residual motor, sensory deficits, speech deficits recorded

12. Preop evaluation Obtain the results of any recent intracranial or diagnostic procedure and consider possibility of residual pneumocephalus. prev. surgeries Drug history Steroid, mannitol, antihypertensive, tricyclic antidepressants,L –dopa, benzodiazepines, phenothiazines,

13. In short – other than routine

14. Anaesthetic considerations Premed Benzodiaepines Antisialogogues May avoid narcotics

15. Transfer Given the value of a head-up posture for controlling ICP, it is recommended that patients with mass lesions be transported with the head of the bed elevated 15–30°.

16. Goals in anaesthesia to facilitate surgical access, minimize nervous tissue trauma and maintain respiratory and cardiovascular stability,(cranial nerves ) VAE prevention and identification CPP, ICP, CMRo2 – comes next in posterior fossa surgery

17. POSITIONS

18. Prone position Minimal neck flexion Face in soft headring with no pressure on eyes and nose Elbow padded No pressure in axilla Abdomen free anterior flexion, abducted and externally rotated genitalgenital nipplenipple

19. SITTING

20. Sitting Not frequently used Craniotomy Good surgical access, CSF drainage, easy airway access Venous return decrease and cardiac output decrease HR no change Venous air embolism

21. Contraindications for sitting position Intracardiac defects Unstable hemodynamics Cachexia Severe hydrocephalus extremes of age Degenerative diseases of cervical spine Significant CVD.

22. Lateral Or Park Bench Position Can be used for access to the post parietal & occipital lobes & lat. post fossa, including tumors at the cerebellopntine angle & aneurysms of the vertebral & basilar arteries.

23. Monitoring The goals of monitoring are to ensure adequate CNS perfusion maintain cardiovascular stability and detect and treat VAE ( venous air embolism )  Five lead ECG, Pulse oximetry, NIBP, IBP  EtCO2 monitoring  Temperature  Central venous catheter  Precordial doppler probe FOR VAE  Esophageal stethoscope  TEE

24. What is special diuresis, blood glucose, hematocrit. Electromyography ICP -- ??? SSEP, MEP ( cranial nerves especially 7 )

25. Special Facial nerve - CP angle tumours – muscle relaxant use to be restricted SSEP – integrity of neural tracts, tension pneumocephalus, spinal cord ischemia Evoked potential – agents BERA – less sensitive to agents – glomus jugulare

26. Anaesthetic technique Induction of anesthesia is a critical time Hypotension, hypertension bradycardia, cough Templehoff's scale – choice of agent and technique

27. Templehoff's scale Easy use; Rapid induction and awakening; Maintenance of perfusion and self-regulation; Prevention of ICP rise Maintenance of vascular reactivity to CO2; Lack of systemic toxicity; Possibility of electrophysiological monitoring; Low cost.

28. Painful times Laryngoscopy, tracheal intubation; Fixing the head in the headrest; Skin, periosteum, and dura matter incision Suture of dura matter and scalp.

29. TIVA Explanation Fentanyl - 1 – 2 mic / Kg Midazolam 1 mg IV Propofol - 1.5 – 2 mg / kg ( 0.1 mg /kg/hour) TCI of 3 – 4.4 mic gm / ml With or without relaxants, Local infiltration ANY WAY – INTUBATE

30. Pros and cons – TIVA Monitoring !! CBF reduced Recovery Awareness Increased complications

31. Balanced GA technique 1) Preoxygenation and self hyperventilation 2.) Thiopentone 3-4 mg/kg IV. 3.) Vecuronium 0.1 mg/kg IV and mask hyperventilation with oxygen and N2O (50:50) until neuromuscular blockade achieved. ISO CAN BE ADDED 4.) Lidocaine 1.5 mg/kg IV and additional thiopentone 2 mg/kg IV just before ET Intubation.

32. Others Rapid sequence is an alternative Maintenance : 1. Fentanyl 5 mic /kg with 0.5 % iso 2.Fentanyl 1.5 mic /kg with 1.5 % iso Isoflurane – mild cerebral vasodilation and less effect on autoregulation

33. RELAXANTS Muscle relaxation is also important during neurosurgery relaxation prevent patient movement at inappropriate time it may decrease ICP by relaxing the chest wall with decrease intra thoracic pressure and encourage venous drainage. Vecuronium – no effect on brain – BUT phenytoin

34. FLUIDS Dry but stable patient is optimum for tumor surgery. Preferably no dextrose Tube fixation – extra care Spontaneous breathing –respiratory structures

35. Emergence It should be smooth and gentle. Lidocaine 1.5 mg/kg IV decrease cough and strain. If surgery is superficial and performed without much traction on the brain stem,-- may extubate. If lesion is deep seated with frequent traction on the brain stem there may be danger of apnea or decrease sensorium with diminish airway reflexes,- keep ventilating - awaken slowly

36. Points to ponder before extubation Level of consciousness Airway and gag reflex Face and tongue edema Airway edema Regular respiratory pattern Stable vital parameters

37. COMPLICATIONS

38. Intraoperative Arrhythmias Ventricular and supraventricular arrhythmias can occur from brain stem stimulation.

39. CVS side effects Hypertension results from stimulation of V th CN, periventricular gray area, reticular formation, or nucleus of tractus solitarius. Bradycardia and escape rhythms results from vagus N stimulation, Hypotension can results from pontine or medullary compression.

40. Venous Air Embolism 25 – 50 % in sitting position That dose not mean it cant happen in other positions

41. Causes open veins & non collapsible venous channels gravitational effects of low CVP neg. I.v. pressure relative to atm. Pressure poor surgical technique

42. Treatment Notify the surgeon to flood the surgical site Lower the operative site Stop N2O administration Give 100% O2 Perform aspiration through a central venous line Consider compression of the jugular veins Provide cardiopulmonary support (fluids, pressors, inotropes)

43. Pneumocephalus

44. Air into the epidural or dural space sufficient to exert a mass effect. Incidence- 3% Sometimes life threatening brain herniation.

45. CAUSES: Diminution of brain volume mannitol, hyperventilation, removal of SOL contraction of intravascular blood vol. associated with acute hemorrhage Gravitational effect of sitting position Intraop drainage of CSF “Inverted Pop Bottle Analogy” as CSF pours out, air bubbles to the top of the container(cranium)

46. Clinical features Confusion Headache Convulsions Neurological deficits Failure to regain conciousness

47. Diagnosis and treatment CT scan confirms the diagnosis and localisation of intracranial air, if untreated Brain herniation and death. Treatment IMMEDIATE twist drill aspiration of air through burr holes on either side of the vertex. Nitrous ??

48. Hydrocephalus Hydrocephalus – CSF obstruction at the level of fourth ventricle

49. MACROGLOSSIA Extreme flexion of head with chin resting on the chest Prolong presence of an oral airway Obstruction of its venous and lymphatic drainage Airway obstruction postop hypoxemia, hypercapnia

50. Tube kinking

51. Quadriplegia Flexion of head on the neck causes streching of the spinal cord at C5 level, regional cord perfusion may be compromised if MAP is decreased.

52. Postop hypertension Post operative hypertensive response following posterior fossa surgery need not be treated aggressively, as this response could be a reactionary response to brain edema

53. Summary Anatomy Tumors Preop Premed Anesthesia – technique, positions, monitors Complications

54. Thank you all