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Post cranial fossa surgery and anesthesia considerations

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Post cranial fossa surgery and anesthesia considerations

  1. 1. Anesthesia for Posterior Cranial Fossa Surgery
  2. 2. Anatomy Three cranial fossae Anterior Middle posterior Located between tentorium cerebelli and foramen magnum
  3. 3. Boundaries Anterior: – Superior border of the petrous temporal bone – Clivus “slope” of occipital,Sphenoid bone • Posterior: – Squamous part of occipital bone • Laterally: – Mastoid part of temporal bone
  4. 4. CONTENTS Cerebellar hemispheres, large portion of the brainstem (lower midbrain, pons and upper medulla)  3rd to 12th cranial nerves nuclei and many efferent and afferent fiber tracts that connect the brain with the rest of the body
  5. 5. Blood supply : Through vertebrobasilar system ,located mostly anteriorly
  6. 6. Foramina/outlets • Foramen magnum (medulla, ascending portion of spinal accessory nerve, vertebral arteries) • Internal accoustic meatus (cranial nerves VII, VIII) • Jugular foramen (IJV, cranial nerves IX, X, XI) • Hypoglossal canal (cranial nerve XII)
  7. 7. Pathology  Tumors:(quite of concern,small space with very vital structures)  Astrocytomas  Medulloblastoma  Hemangioblastoma  CP angle tumors  Metastatic disease  Vascular pathology hematoma, aneurysm  Infection/ inflammatory
  8. 8. Anesthetic Considerations
  9. 9. Overall goal • facilitate surgical access • maintain respiratory and cardiovascular stability • minimise nervous tissue trauma
  10. 10. Pre-op evaluation • Complete medical history with diagnostic procedures & review of medicines • Thorough physical/neurologic examination
  11. 11. Clinical features  Hydrocephalus: features of raised ICP  Nausea  Vomiting  Headache  Altered consciousness  Range of other symptoms  Dysphagia, laryngeal dysfunction  Visual disturbances  Hearing impairment  Weakness or numbness in face  Difficulties with balance and walking
  12. 12. Investigations • CBC • RFTs • Coagulation profile • Random blood sugar • CXR • ECG • CT/MRI
  13. 13. Pre-op preparation • Thorough neurologic assessment • Adequate units of blood should be arranged and cross matched • Extra, large bore IV cannula
  14. 14. Intra-op Monitoring: • HR • ECG • NIBP • IBP • SpO2 • CVP • Urine output: Foley’s catheter • ETCO2 • Precordial Doppler • TEE
  15. 15. Positioning • Positions – Sitting – Prone – Lateral/ park bench position
  16. 16. semirecumbent in the standard sitting position :the back is elevated to 60°, and the legs are elevated with the knees flexed. The head is fixed in a three-point holder with the neck flexed; the arms remain at the sides with the hands resting on the lap.
  17. 17. Sitting position – Used for some posterior fossa and cervical spine surgery – Advantages • Better venous and CSF drainage (↓ICP) • Better surgical access • Decreased blood loss • Better facial view for cranial evoked responses
  18. 18. Disadvantages – Possibly greater dangers than alternative positions • Hypotension, cerebral ischemia (decreased CPP) – Volume loading and pressors to maintain CPP ≥60 mmHg – Perfusion pressure should be measured at ear level – TED stockings or calf compression devices
  19. 19. • Tongue and pharynx compression or spinal injury from neck flexion • Pressure areas: buttocks, potential brachial plexus distraction • Venous air embolism ± paradoxical embolism • Pneumocephalus – May be worsened by N2O diffusion after dural closure – Cease N2O with dural closure
  20. 20. Prone position • facial skin ulcerations can occur from uneven pressure distribution when the horseshoe headrest is used • Post operative Visual Loss (POVL) eye compression and retinal ischaemia • Other pressure areas: elbows, breasts, iliac crests, genitalia, knees, toes
  21. 21. • Abdominal pressure: increased PAW, IVC obstruction • Neck flexion may cause compression of base of tongue and pharynx – Especially with instrumentation: ETT, TEE
  22. 22. Park-bench position
  23. 23. • Can be used for post parietal & occipital lobes & lat. post fossa, including tumors at the cerebellopntine angle & aneurysms of the vertebral & basilar arteries.
  24. 24. Conduct of Anesthesia
  25. 25. • Induction/Airway: Standard induction, ETT • Surgical Course: Head Pinning by surgeon (very painful, deepen Anesthesia just prior) • Significant blood loss possible from Scalp • careful positioning
  26. 26. Complications
  27. 27. • Hypotension • Measures to avoid hypotension: – Prepositioning hydration – Wrapping of the legs with elastic bandages to counteract gravitational shifts of blood – Slow, incremental adjustment of table position. – Aggressive volume loading and the G suit (also known as pneumatic antishock trousers) attenuate the effects of assuming the sitting position.
  28. 28. Intra operative complications  CVS reflexes:  Brain stem injury  Bradycardia:  Stimulation of vagus nerve  Changes in BP:  Hypertension: stimulation of floor of 4th ventricle, medullary reticular formation or trigeminal nerve  Mgmt:  Inform surgeon  Pharmacological Rx: if recurrent
  29. 29. Injury to cranial nerves  Usu during work on cerebro-pontine area Intra operative stimulation of cranial nerves : V, VII, VIII, XI, XII ?Use of muscle relaxants
  30. 30. Venous Air Embolism  Occur when the pressure within an open vein is subatmospheric.  Can occur in any position/procedure whenever the surgical above heart(but usu significant > 20cm)  Incidence: highest during sitting craniotomies (40- 45%
  31. 31. Massive VAE Vs Gradual air entrainment Massive VAE • Less common • Abrupt,catastrophic hemodynamic response Slow air Entrainment • More common • Slow air entrainment over longer period • Little respi/hemodynamic compromise • But↑PVR & ↑ PAP & RAP • ↑ dead space,↓EtCO2, ↑PaCO2
  32. 32. Findings • Decrease in EtCO2 • Increase in PaCO2 • Decrease in PaO2 • Decreased CO • ?EtN2 • Mill wheel murmur
  33. 33. Prevention: • Positioning (prone vs sitting) • Adequate hydration (avoid hypovolemia) • ?Use of PEEP
  34. 34. Monitoring for VAE • Precordial Doppler sonography: • Interruption of the regular swishing of the Doppler signal by sporadic roaring sounds indicates venous air embolism • TEE • ETCO2 • ETN2 • PA catheter
  35. 35. Precordial doppler • Sensitive, can detect 1 mL of air or less (but NOT quantitative!) • usu positioned @ middle 3rd sternum on the right • Position be confirmed by injecting 0.5-1ml air
  36. 36. Transesophageal echocardiography (TEE) • More sensitive than Doppler ultrasound • Specific, because air bubbles are visualized directly • The only monitor that can detect PA • Expensive, requires special expertise, and demands near constant attention
  37. 37. Management:  Prevent further air entry  Notify surgeon (flood or pack surgical field)  Jugular compression  Lower the head  Durants’ position  Treat intravascular Air  Aspirate right heart catheter  Discontinue N2O  FIO2: 1.0  Pressors/inotropes  Chest compression
  38. 38. Paradoxical air embolism • In patients with Patent foramen ovale (PFO) • In patients with probe PFO, when normal transatrial pressure is reversed : • Hypovolemia • PEEP • TRANSPULMONARY PASSAGE OF AIR: – Large volumes (>20ml/kg oR > 0.3ml/kg/min)
  39. 39. Post op complications • Ventilation/airway abnormalities – Macroglossia • CVS complications: HTN • Neurologic complications: • Pneumocephalus • Quadriplegia
  40. 40. Macroglossia • Venous obstruction due to sustained neck flexion • Also attributed to prolonged ischemia due to FB: Airways
  41. 41. Pneumocephalus:
  42. 42. • Cause delayed awakening and continued impairment of neurological status • Related with N2O use • The treatment is a twist-drill hole followed by needle puncture of the dura.
  43. 43. Quadriplegia • Due to compression on the cervical spinal cord • Caution with degenerative diseases of the cervical spine
  44. 44. References: • http://www.frca.co.uk/article.aspx?articleid=1 00662 • Handbook of Neuroanesthesia, 4th edition: Philippa Newfield, James E. Cottrell • Millers’ anesthesia:7th edition • Clinical Anesthesiology: 4th edition: Morgan, Mikhail, Murray

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