Anaesthesia for ophthalmic surgery
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Anaesthesia for ophthalmic surgery
- 1. Anaesthesia for Ophthalmic Surgery Anatomy, Physiology and Practice T Mphanza FRCA, FFICM 1
- 2. Special Considerations • Proximity to airway • Age • Anatomy • Physiology 2
- 3. 3
- 4. Anatomy • Orbit - irregular pyramid • Base at the front • Axis - points postero-medially • Optic foramen forms the apex 4
- 5. Anatomy • Orbit - irregular pyramid • 40 - 50 mm deep • Volume - 30 mls • globe - 7 mls 5
- 6. Anatomy • Globe • Anteriorly • Closer to the roof • Nearer to the lateral wall • Axial length - 25 mm 6
- 7. Anatomy 7
- 8. Anatomy • Extraocular muscles • 4 rectus muscles • 2 oblique muscles 8
- 9. LR6(SO4)3 9
- 10. Sensory Innervation • Trigeminal •V 1 • Supratrochlear, Supraorbital, Long ciliary, Nasociliary, Infratrochlear, Lacrimal •V 2 • Infraorbital, Zygomatic 10
- 11. Autonomic Innervation • Sympathetic • Superior cervical ganglion • Mydriasis • Parasympathetic • Fibres from III • Miosis 11
- 12. 12
- 13. Blood Vessels • Arterial • Ophthalmic artery • Venous • Ophthalmic veins • Superior • Inferior 13
- 14. Anatomy and Physiology 14
- 15. Physiology • Aqueous humour • Produced by ciliary body • Carbonic anhydrase • Drainage • Venous channels • SVC 15
- 16. Physiology • Intraocular pressure (IOP) • Range 10 - 20 mmHg • Increases with age • Direct correlation with axial length • Main determinant is aqueous humour 16
- 17. Physiology • Factors affecting IOP • Arterial BP • Auto-regulation • Venous BP • Valsalva, coughing, straining • Partial pressures - CO , O 2 2 17
- 18. Events that Decrease IOP • IV anaesthetics • Volatile anaesthetics • Mannitol • Timolol 18
- 19. Events that Increase IOP • Succinylcholine • Direct laryngoscopy • Hypoventilation 19
- 20. 20
- 21. Oculomedullary Reflexes • Oculocardiac • Trigemino-vagal: • Bradycardia, ectopics, sinus arrest • Oculorespiratory • Oculoemetic 21
- 22. Anaesthetic Ramifications of Ophthalmic Drugs 22
- 23. • Ecothiopate • Anticholinesterase miotic • Cyclopentolate • Mydriatic • Phenylephrine • Mydriatic 23
- 24. • Acetazolamide • Carbonic anhydrase inhibitor • Timolol • Beta blocker • Sulphur hexafluoride • Inert gas 24
- 26. • Akinesia • Profound analgesia • Minimal bleeding • Avoidance of oculocardiac reflex 26
- 27. • Control of IOP • Awareness of drug interactions • Emergence without coughing, straining or vomiting 27
- 28. Anaesthesia Techniques • General • Local • Topical • Regional 28
- 29. Factors that Influence Choice of Anaesthesia • Nature and duration of procedure • Coagulation status • Patient’s choice • Ability to communicate and cooperate 29
- 30. General Anaesthesia • Volatile vs TIVA • ETT vs LMA 30
- 31. General Anaesthesia • Special consideration • Head up tilt • Avoid hypercapnoea • Avoid N O in vitreoretinal surgery 2 • Smooth emergence 31
- 32. Topical Anaesthesia • Instillation of LA drops • Advantages • Minimal complications • Limitations • Lack of akinesia • Only suitable for uncomplicated cases 32
- 33. Regional Anaesthesia • Sub-Tenon • Peribulbar (Extra-conal) • Retrobulbar (Intra-conal) 33
- 34. Sub-Tenon’s Block • Tenon’s capsule • Dense fascial sheath surrounding the globe and extraocular muscles from the limbus to the optic nerve 34
- 35. Sub-Tenon’s Block • Sensory block • Short-ciliary nerves pass through Tenon’s capsule to globe • Akinesia • Direct blockade of ant. nerve fibres as they enter extra-ocular muscles 35
- 36. Retro & Peribulbar Blocks 36
- 37. Retrobulbar Block 37
- 38. Complications of Regional Blocks • Stimulation of oculocardiac reflex • Haemorrhage • Superficial • Retrobulbar • Retinal perfusion compromise • Loss of vision 38
- 39. Complications of Regional Blocks • Globe penetration • Intra-arterial injection • Trauma to optic nerve • Optic sheath injection 39
- 40. Complications of Regional Blocks • Extraocular muscle injury • Central retinal artery occlusion • Accidental brainstem anaesthesia 40
- 41. Anaesthetic Management of Specific Situations 41
- 42. • Open Eye, Full Stomach • Aspiration vs Blindness • Strabismus surgery • OCR • MH • PONV 42
- 43. • Intraocular Surgery • Glaucoma, vitrectomy, cataracts • IOP control • Complete akinesia • Continuation of miotics • Provide an antiemetic effect 43
- 44. • Retinal Detachment Surgery • SF injection for tamponade 6 • IV acetazolamide or mannitol • Akinesia is not critical 44
- 45. General Vs. Regional Anaesthesia 45
- 46. • Regional Techniques • Day stay surgery • Better akinesia • Less PONV • Less effect on IOP 46
- 47. Evidence Based Medicine • Cochrane Reviews • Peribulbar Vs. Retrobulbar • Sub-Tenon’s Vs. Topical 47
- 48. Evidence Based Medicine - CRTs • General Vs Regional for Cataract Surgery • Cognitive Function • Perioperative MI • Plasma catecholamine response 48
- 49. Summary • Anatomy and Physiology • Drug interactions • Special Requirements • Management of Specific Situations 49