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Anaesthesia for Ophthalmic
SurgeryAnatomy, Physiology and Practice
T Mphanza FRCA, FFICM
1
Special Considerations
•Proximity to airway
•Age
•Anatomy
•Physiology
2
3
Anatomy
•Orbit - irregular pyramid
•Base at the front
•Axis - points postero-medially
•Optic foramen forms the apex
4
Anatomy
•Orbit - irregular pyramid
•40 - 50 mm deep
•Volume - 30 mls
•globe - 7 mls
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Anatomy
•Globe
•Anteriorly
•Closer to the roof
•Nearer to the lateral wall
•Axial length - 25 mm
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Anatomy
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Anatomy
•Extraocular muscles
•4 rectus muscles
•2 oblique muscles
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LR6(SO4)3
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Sensory Innervation
•Trigeminal
•V1
•Supratrochlear, Supraorbital, Long ciliary, Nasociliary, Infratrochlear, Lacrimal
•V2
• Infraorbital, Zygomatic
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Autonomic Innervation
•Sympathetic
•Superior cervical ganglion
•Mydriasis
•Parasympathetic
•Fibres from III
•Miosis
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12
Blood Vessels
•Arterial
•Ophthalmic artery
•Venous
•Ophthalmic veins
•Superior
•Inferior
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Anatomy and Physiology
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Physiology
•Aqueous humour
•Produced by ciliary body
•Carbonic anhydrase
•Drainage
•Venous channels
•SVC
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Physiology
•Intraocular pressure (IOP)
•Range 10 - 20 mmHg
•Increases with age
•Direct correlation with axial length
•Main determinant is aqueous humour
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Physiology
•Factors affecting IOP
•Arterial BP
•Auto-regulation
•Venous BP
•Valsalva, coughing, straining
•Partial pressures - CO2 , O2
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Events that Decrease IOP
• IV anaesthetics
• Volatile anaesthetics
•Mannitol
• Timolol
• Betaxolol
•NDMR
•Hyperventilation
•Hypothermia
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Events that Increase IOP
• Succinylcholine
• Direct laryngoscopy
• Hypoventilation
• Arterial hypoxaemia
• Increased venous pressure
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Oculomedullary Reflexes
•Oculocardiac
•Trigemino-vagal:
•Bradycardia, ectopics, sinus arrest
•Oculorespiratory
•Oculoemetic
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Anaesthetic Ramifications of
Ophthalmic Drugs
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•Ecothiopate
•Anticholinesterase miotic
•Cyclopentolate
•Mydriatic
•Phenylephrine
•Mydriatic
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•Acetazolamide
•Carbonic anhydrase inhibitor
•Timolol
•Beta blocker
•Sulphur hexafluoride
•Inert gas
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Requirements for Ophthalmic
Surgery
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•Akinesia
•Profound analgesia
•Minimal bleeding
•Avoidance of oculocardiac reflex
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•Control of IOP
•Awareness of drug interactions
•Emergence without coughing, straining or vomiting
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•General
•Local
•Topical
•Regional
Anaesthesia Techniques
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Factors that Influence Choice of
Anaesthesia•Nature and duration of procedure
•Coagulation status
•Patient’s choice
•Ability to communicate and cooperate
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General Anaesthesia
•Volatile vs TIVA
•ETT vs LMA
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General Anaesthesia
•Special consideration
•Head up tilt
•Avoid hypercapnoea
•Avoid N2O in vitreoretinal surgery
•Smooth emergence
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Topical Anaesthesia
•Instillation of LA drops
•Advantages
•Minimal complications
•Limitations
•Lack of akinesia
•Only suitable for uncomplicated cases
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Regional Anaesthesia
•Sub-Tenon
•Peribulbar (Extra-conal)
•Retrobulbar (Intra-conal)
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Sub-Tenon’s Block
•Tenon’s capsule
•Dense fascial sheath surrounding the globe and extraocular muscles from the limbus to the optic nerve
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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
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Retro & Peribulbar Blocks
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Retrobulbar Block
Complications of Regional Blocks
•Stimulation of oculocardiac reflex
•Haemorrhage
•Superficial
•Retrobulbar
•Retinal perfusion compromise
•Loss of vision
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Complications of Regional Blocks
•Globe penetration
•Intra-arterial injection
•Trauma to optic nerve
•Optic sheath injection
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Complications of Regional Blocks
•Extraocular muscle injury
•Central retinal artery occlusion
•Accidental brainstem anaesthesia
40
Anaesthetic Management of
Specific Situations
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•Open Eye, Full Stomach
•Aspiration vs Blindness
•Strabismus surgery
•OCR
•MH
•PONV
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•Intraocular Surgery
•Glaucoma, vitrectomy, cataracts
•IOP control
•Complete akinesia
•Continuation of miotics
•Provide an antiemetic effect
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•Retinal Detachment Surgery
•SF6 injection for tamponade
•IV acetazolamide or mannitol
•Akinesia is not critical
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General Vs. Regional
Anaesthesia
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•Regional Techniques
•Day stay surgery
•Better akinesia
•Less PONV
•Less effect on IOP
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•Cochrane Reviews
•Peribulbar Vs. Retrobulbar
•Sub-Tenon’s Vs. Topical
Evidence Based Medicine
47
Evidence Based Medicine - CRTs
•General Vs Regional for Cataract Surgery
•Cognitive Function
•Perioperative MI
•Plasma catecholamine response
48
Summary
•Anatomy and Physiology
•Drug interactions
•Special Requirements
•Management of Specific Situations
49